THE OPISTHOBRANCHS OF CAPE ARAGO. OREGON.
WITH NOTES ON THEIR NATURAL HISTORY AND
A SUMMARY OF BENTHIC OPISTHOBRANCHS
KNOWN FROM OREGON
by
JEFFREY HAROLD RYAN GODDARD
A THESIS
Presented to the Department of Biology
and the Graduate School of the University of Oregon
in partial fulfillment of the requirements
for the degree of
Master of Science
December 1983
!tIl.
I :'"
i
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1
APPROVED: -------:n:pe:;-;t::;e:;:-rt;l;1T:-.JF~r:aaD:inkk---
ii
iii
An Abstract of the Thesis of
Jeffrey Harold Ryan Goddard
in the Department of Biology
for the degree of
to be taken
Master of Science
December 1983
TITLE: THE OPISTHOBRANCHS OF CAPE ARAGO, OREGON, WITH NOTES ON THEIR
NATURAL HISTORY AND A SUM}~Y OF BENTHIC OPISTHOBRANCHS KNOWN
FROM OREGON
Approved:
Peter W. Frank
The opisthobranch molluscs of Oregon have been little studied, and
little is known about the biology of many species. The present study
consisted of field and laboratory observations of Cape Arago opistho-
branchs. Forty-six species were found, extending the range of six north-
ward and two southward. New food records are presented for nine species;
an additional 20 species were observed feeding on previously recorded
prey. Development data are given for 21 species. Twenty produce plank-
totrophic larvae, and Doto amyra produces lecithotrophic larvae, the
first such example known from Eastern Pacific opisthobranchs. Hallaxa
chani appears to be the first eudoridacean nudibranch known to have a
subannual life cycle. Development, life cycles, food and competition,
ranges, and the ecological role of nudibranchs are discussed. Nudi-
iv
branchs appear to significantly affect the diversity of the Cape Arago
encrusting community. T~e 66 (possibly 71) benthic opisthobranchs cur-
rently known from Oregon are listed and discussed.
8:····..~
v
VITA
NAME OF AUTHOR: Jeffrey Harold Ryan Goddard
PLACE OF BIRTH: San Rafael, California
DATE OF BIRTH: February 5, 1955
UNDERGRADUATE AND GRADUATE SCHOOLS ATTENDED:
University of California at Santa Cruz
University of Oregon
DEGREES AWARDED:
Bachelor of Arts, 1977, University of California at Santa Cruz
AREAS OF SPECIAL INTEREST:
Marine and Community Ecology
Invertebrate Zoology
Biology of Opisthobranch Molluscs
PROFESSIONAL EXPERIENCE:
Graduate Teaching Fellow, Department of Biology, University of
Oregon, Eugene, 1979-1982
AWARDS AND HONORS:
Cum Laude Society, 1973
Bachelor of Arts with Honors, 1977
PUBLICATIONS:
Goddard, J. 1973. Opisthobranchs of San Francisco Bay. Tabulata
6:8-10.
Goddard, J.H.R. 1981. Range extension and notes on the food, mor-
phology, and color pattern of the dorid nudibranch Hallaxa chani.
The Veliger 24:155-158.
vi
ACKNOWLEDGEMENTS
I would like to thank Dr. Terry Gosliner of the California Academy
of Sciences for identifying specimens of Cuthona cocoachroma, Sandra
Millen of the University of British Columbia for identifying specimens
of Anisodoris lentiginosa, Adalaria sp., and Onchidoris muricata, Drs.
John and Dorothy Soule of the Allan Hancock Foundation, University of
Southern California and Patricia Cook of the British Museum (Natural
History) for examining and identifying specimens of Hincksina minuscula,
and Dr. Cadet Hand, Director, Bodega Marine Laboratory and Dr. Frederick
Bayer, Curator, Department of Invertebrate Zoology, Smithsonian Institu-
tion for examining specimens of the alcyonacean octocoral prey of
Tritonia festiva. I am indebted to Dr. Paul Rudy, Director, Oregon In-
stitute of Marine Biology and Jean Hanna, O.I.M.B. Librarian, for use of
the facilities at O.I.M.B. and for their support and encouragement. Tom
Wayne and Katheryn Young provided specimens and much provocative discus-
sion. Elizabeth Hill's sharp eye and inquisitive mind aided greatly in
the field and stimulated many interesting and useful discussions. My
thanks also to Dr. Stanton Cook and two anonymous reviewers for The
Veliger for critically reviewing the manuscript. Marge Lebow's typing
Itt vii
expertise is greatly appreciated.
Most of all I would like to thank Dr. Peter W. Frank, my major ad-
visor, for his support, advice, very helpful review of the manuscript,
and the many stimulating discussions •. He was always willing to listen,
gave freely of his ideas, and allowed me to pursue my own interests.
TABLE OF CONTENTS
INTRODUCTION.
STUDY AREA AND DATES OF OBSERVATION •
North Cove.
Middle Cove
South Cove
Good Witch Cove •
METHODS
NATURAL HISTORY OBSERVATIONS
DISCUSSION
Life Cycles
Development
Food and Competition
Ranges
The Effects of Nudibranch Predation on the Diversity
of the Encrusting Animal Community at Cape Arago
Benthic Opisthobranchs Known from Oregon.
BIBLIOGRAPHY.
viii
Page
1
3
3
5
6
7
8
10
42
42
44
45
50
51
57
68
LIST OF TABLES
ix
Table Page
l. Larval Development of Cape Arago Opisthobranchs. 12
2. Results of Anisodoris nobilis Food Preference
Experiment 19
3. Prey of Cape Arago Opisthobranchs 47
4. Benthic Opisthobranchs Known from Oregon 58
ILIST OF FIGURES
Figure
1. Cape Arago (430 Z0'N; 124°2Z'W) •
x
Page
4
\~
1
INTRODUCTION
The opisthobranch molluscs of Oregon have been little studied com-
pared with those of California to the south and those of the San Juan
Archipelago-Vancouver Island region to the north. Sowell (1949) studied
the natural history of opisthobranchs in the Coos Bay-Cape Arago area in
the late 1940's and lists 19 species from that area. Since then two
relatively brief studies of Oregon opisthobranchs have been made. Sphon
(1972) reviewed the literature mentioning Oregon opisthobranchs and re-
ported on a six day collecting trip made in five Oregon localities.
Belcik (1975) lists species not reported by Sphon that he found in the
Coos Bay-Cape Arago area while studying parasites of molluscs and fish.
A total of 43 benthic opisthobranchs were reported in these three studies,
21 from Cape Arago.
Members of the order Nudibranchia comprise most of the rocky inter-
tidal opisthobranchs. While little is known about the biology and ecol-
ogy of many Northeastern Pacific species (Beeman and Williams, 1980),
those nudibranchs that have received study have all been shown to be
carnivores which prey, as a group, on a wide variety of sessile
2invertebrates (Thompson, 1976; McDonald and Nybakken, 1978; Beeman and
Williams, 1980). Little is known about the effects of their predation
on the encrusting communities to which they belong.
In this paper I report on observations, scattered over a 45 month
period beginning in December 1979 and ending in September 1983, of rocky
intertidal opisthobranchs from Cape Arago. The purpose of this research
was to 1) determine which species occur at Cape Arago, 2) find out as
much as possible about aspects of their biology, including their food,
feeding methods, larval development, and, in a few cases, their life
cycles, and 3) attempt to gain some understanding of the effects of their
predation on the encrusting community at Cape Arago. Observations are
presented for each of the 46 species I found, followed by a general dis-
cussion and a list and discussion of the benthic opisthobranchs present-
ly known from Oregon.
~.i~~ 3
STUDY AREA AND DATES OF FIELD OBSERVATION
Cape Arago contains one of the widest, most physically and biolog-
ically diverse intertidal areas between Cape Mendocino, California and
Cape Flattery, Washington (Dr. P.W. Frank, pers. corom.; Dr. J.J. Gonor,
pers. corom.; per. obs.). The study area included North, Middle, and
South Coves of Cape Arago and one small cove located just south of Cape
Arago which I call Good Witch Cove (Fig. 1). Cape Arago is situated 7.3
kID southwest of the entrance to Coos Bay. Charleston and the Oregon In-
stitute of Marine Biology are located just inside the south side of the
mouth of Coos Bay.
North Cove
North Cove has the largest intertidal area of the four coves. At
low tide one can walk beyond Shell Island to the outer boulder field and
edge of the Macrocystis-Nereocystis kelp bed located just inside Simpson
Reef. North Cove contains a mixture of sandstone shelves, outcrops,
and boulders of variable size and is protected from large surf by
Pacific
Ocean
CAPE ARAGO
1 km
1
N
I
4
Figure 1. o 0Cape Arago (43 20'N; 124 22'W)
Simpson Reef.
5
Forty-two of 65 trips comprising this study were made to
~I~
the inner boulder field, one of the most sheltered parts of North Cove
(Fig. 1). This boulder field consists of roughly half fissured and
pocketed bedrock and half boulders averaging 0.25 to O.Sm in diameter.
During the calmer months (spring and summer) much of the inner boulder
field is subject to silt and detritus accumulation. Few sea urchins
are present, and the area is dominated by the algae Egregia menziesii,
Hedophyllum sessile, Iridea flaccida, Cystoseira osmundacea, Laminaria
sp., the introduced Sargassum muticum, and the surfgrass Phyllospadix.
The undersides of boulders and ledges support a rich variety of sessile
invertebrates - the prey of most nudibranchs - and it is under and among
these boulders that the greatest number of opisthobranch species and in-
dividuals occurring at Cape Arago are found (38 out of the Cape Arago
total of 46).
A total of 44 trips were made to North Cove in the following months:
12/79; 3,5,6,7/80; 6/81-5/82; 8,9/82; and 3-9/83. Trips from 10/81 to
2/82 were at night and covered a relatively small portion of the inner
boulder field.
Middle Cove
Middle Cove contains the next largest intertidal area of Cape Arago,
and, like North Cove, contains a mixture of sandstone bedrock, boulders,
and outcrops of varying size. However, Middle Cove is more exposed to
surf and possesses a-number of invertebrates rare or absent in the North
•
Cove inner boulder field. Among these are the hydrocoral Allopora
6
~...".....'·'~1.y
porphyra (Fisher, 1931), the coral-like ectoproct Heteropora alaskensis
Borg, 1933, and the solitary coral Balanophyllia elegans Verrill, 1864.
An undescribed white alcyonacean octocoral (see Tritonia festiva) is
abundant. Where sea urchins are sparse, Middle Cove supports diverse
and luxuriant invertebrate and algal communities. Middle Cove appears
to possess the highest hydroid and sponge diversity of any of the coves.
In ten trips here (made in months of 3,7,8/80; 6,8,/81; 5-8/83) I found
28 species of opisthobranchs.
South Cove
The west side of South Cove consists of a small boulder field semi-
protected from surf. As one moves toward the point separating Middle
and South Coves, surf exposure increases and the substrate becomes solid
rock with deep surge channels. Not as many species and individuals of
opisthobranchs occur at South Cove. I found 10 species on five trips
2,5/80; 5/81; 6,7/82), and none of the species was ever abundant. The
low number of opisthobranchs here may be related to the smaller size of
the low-intertidal boulder field - much of the area consists of urchin
or Phyllospadix-dominated bedrock. For unknown reasons hydro ids are
rare at South Cove.
,.a.·~
7
Good Witch Cove
This is the most surf-exposed of the coves and is accessible only
on the lowest tides when the swell is small. The substrate consists of
pocketed and fissured bedrock overlain with patches of boulders. Many
of these boulders are relatively barren of organisms - probably the re-
suIt of grazing by the large numbers of urchins, limpets, and chitons
present and perhaps also the result of boulder-overturning by surf.
However, the undersides of many ledges and larger boulders support a
rich invertebrate fauna. I found 18 opisthobranch species here on six
trips (5,6,7/80; 5/82; 5,7/83).
8METHODS
Opisthobranch prey species were determined by observing close assoc-
iation of the opisthobranch and its possible prey in the field and by
laboratory observation of feeding. Gut contents also were occasionally
examined.
Observations on egg masses and larval development were largely re-
stricted to species for which no other data currently exist. To make
these observations. opisthobranchs were first separated by species into
dishes or jars. A newly laid egg mass was scraped off the side of the
container. examined. and transferred to a separate. labelled jar. The
water in these jars was changed everyone or two days. and all jars were
kept in a flowing seawater bath (100 to 170 C). Separated egg masses
were examined daily until veligers had hatched. at which time veliger
shell lengths were measured. All measurements of eggs and veligers
were made with a compound microscope equipped with an ocular micrometer.
Owing to the discontinuity of field observations little can be con-
cluded about the seasonality of most of the opisthobranch species. North
Cove was observed in every month of the year (though continuously only
9for one year), and conclusions about seasonality are presented for a
few of the species found there. These should be considered tentative.
10
NATURAL HISTORY OBSERVATIONS
Acanthodoris nanaimoensis O'Donoghue, 1921
This dorid occurred rarely at all four coves. I found a total of
seven specimens ranging in length from 5 to 22mm.
Adalaria sp.
I found ten specimens of this white dorid, ranging in length from
4 to 15mm in March, April, August, and September at North Cove. Sandra
Millen (pers. comm.) informs me that this is one of three Adalaria species
found in British Columbia and is not species 138 in Behrens (1980). She
further states: "It can be recognized by the elongate body, wider at
the front end, and by the spicules which project out of the top of the
tubercles in a radiating pattern."
Five Adalaria sp. were found on the anascan bryozoan Hincksina
minuscula (Hincks, 1882) on the undersides of boulders. Laboratory ob-
servations confirmed that Adalaria sp. feeds on this bryozoan. The
11
Onchidorididae are known to use the radula to open the frontal membranes
or opercula of their bryozoan prey and then use a muscular buccal diver-
ticulum as a pump to suck out the zooids (Thompson, 1976). After plac-
ing fresh pieces of Hincksina minuscula with Adalaria sp. specimens for
a day, such feeding was evidenced by the many empty zooecia possessing
partially attached frontal membranes.
The egg mass of Adalaria sp. is a white ribbon laid on edge in a
coil of 2 to 4 turns. Egg masses are 1 - 2mm high and 4 - 10mm in diam-
eter. For data on the larval development of this and other species see
Table 1.
Aeolidia papillosa (Linnaeus, 1761)
This eolid is frequent at North Cove. Specimens ranged in length
from 5 to 55mm and often occurred next to Epiactis prolifera Verrill,
1869, an abundant anemone upon which Aeolidia papillosa readily feeds
in the laboratory (pers. obs.).
Aldisa cooperi Robilliard and Baba, 1972
I found three specimens, one at Middle Cove in June 1981, and two
at Good Witch Cove in May and July 1983. The first two were 22mm and
27mm long respectively, orange-yellow in color, and had, respectively,
9 and 8 small black dots on the midline of the dorsum between the
rhinophores and gills.
Aldisa cooperi was originally described as a subspecies of Aldisa
'¢JJ •
Table 1. Larval development of Cape Arago opisthobranchs
..
Diameter of ova Embryonic Culture Length of5veliger eyespots(,um) 2 3 ova per period Temp. shell shell 1 (pili) at
Species range1 month N capsule (days) (oC) type4 range N3 hatching
Adalaria 81.2 April 3 1 11 10-12 1 136.0 3 no
sp. 83.7 143.5
Ancula 58.3 June 2 1 9 14-16 1 103.8 1 no
pacifica 59.0
Anisodoris 83.0 June 1 up to 20 14 14-17 1 152.8 1 no
nobilis
Aplysiopsis 66.0 July 1 1 7 15-17 1 112.9 1 no
smithi
Berthella 92.6 May 1 1-2 18 11-14 1 152.7 1 yes
californica
Cadlina 91.0 155.6
modesta 92.0 April 3 1 16-19 12-15 1 158.4 4 no
Catriona 99.7 July 1 1 10 15-17 2 273.9 1 yes
columbiana
Crimora 71.6 115.5
coneja 74.2 April 3 1 17-18 10-14 1 123.5 3 no
I-'
N
~ "iIiiI ..
Table 1 (cont.)
Diameter of ova Embryonic Culture Length of5veliger eyespots
1Cpm) 2 3 ova per period Temp. shell shell 1 (pm) at
Species range month N capsule (days) (oC) type4 range N3 hatching
Cuthona
cocoachroma 96.3 July 1 1 6 15-17 2 256.7 1 no
Diaphana 122.1
californica 73.2 Sept. 1 1 7-8 12-16 1 123.6 2 no
Discodoris
heathi 76.8 June 1 4-7 15 14-17 1 144.8 1 no
Doto 149.6 236.0
amyra 154.3 May 4 1 19-21 15-17 1 238.5 2 yes
Doto
kya N75 July 1 1 7 15-17 1 122.3 1 no
Eubranchus
rustyus 92.9 July 1 1 6 15-17 2 240.1 1 yes
Hallaxa 79.6 147.9
chani 82.6 May 4 1 15-17 11-15 1 154.1 3 no
--
Laila
cockerelli 95.4 April 1 1 17 10-13 1 141. 8 1 no
I-'
LV
~ .. •
Table 1 (cont.)
Diameter of ova Embryonic Culture Length of5veliger eyespots
l{pm) 2 3 ova per period Temp. shel~ shell 1 (pm) at
Species range month N capsule (days) (DC) type range N3 hatching
Onchidoris 75.0 128.5
muricata 77 .3 April 2 1 10-11 7-11 1 135.6 3 no
Onchidoris 62.6 113.3
sp. 64.0 Sept. 4 1 9-11 12-16 1 116.6 4 no
Precuthona
divae 107.1 July 1 1 8 15-17 2 249.1 1 no
---
Triopha
catalinae
--
Aug 1 10 14-18 1 rJ 130 1 no
Tritonia
festiva 78.9 June 1 1 12 14-17 1 125 1 yes
1 Range of Means means calculated from
measurements (usually ten) of ova (or
veliger shells) from a single egg mass
2 month in which egg masses
laid
3 N = number of egg masses
in which ova (or veliger
shell lengths) measured
4 See Hurst (1967)
5 Length = longest
dimension of shell
,....
.j:--
15
sanquinea. However, Bertsch and Johnson (1982), on the basis of sympatry,
and Millen (pers. comm.), on the basis of anatomy, consider them to be
separate species. With this in mind, I kept one specimen of both species
together in a jar to see if mating and egg-laying would occur. The A.
cooperi measured 27mm in length, and the ~. sanquinea 20mm. After one
month in captivity (12o-16oC), and what appeared to be a number of mat-
ings, the A. sanquinea laid an egg mass. The embryos stopped developing
at about the 32-cell stage. While I can not rule out other factors,
this may indicate that interbreeding occurred but resulted in inviable
hybrid embryos, and thus support the conclusion that A. cooperi and A.
sanquinea are distinct species.
Aldisa sanquinea (Cooper, 1863)
One bright red specimen, 26mm long and lacking dark spots on the
dorsum, was collected at North Cove by the spring 1982 Oregon Institute
of Marine Biology invertebrate zoology class. I found another specimen,
red-orange in color, 20mm long, and also lacking dark spots, at Good
Witch Cove in May 1983.
Ancula pacifica MacFarland, 1905
This species is frequent at North Cove and was most common during
spring and early summer. Ancula pacifica usually occurred under boulders,
and in June 1983 I found eight specimens with egg masses among the ento-
proct Barentsia sp. on the undersides of boulders. Many of these
~.~.
16
Barentsia individuals lacked a calyx - most likely as a result of graz-
ing by Ancula pacifica. Ancula pacifica is known to feed on Barentsia
ramosa (Robertson, 1900) in California (McDonald and Nybakken, 1978).
Before spring 1983, all the Ancula pacifica I had observed at Cape
Arago had the color pattern described by Robilliard (1971b) for the two
specimens he found in Washington. These specimens lack orange lines on
the body but do possess orange-tipped rhinophores, accessory rhinophore
papillae, gills, and extrabranchial papillae. In spring and summer 1983
I noticed the above form of Ancula pacifica as well as the more typical
furm (which has orange lines on the body and is common in California) at
North Cove. Northern and southern forms of Ancula pacifica may exist.
The egg mass of Ancula pacifica is a white, slightly flattened,
tapering cord. The cord is not laid in a spiral.
Anisodoris lentiginosa Millen. 1982
On 18 May 1980 I found one specimen crawling on bare rock in a pool
at Good Witch Cove. It was about 90mm long, light yellow in color, and
had six small, dark brown blotches scattered on the central part of the
anterior two-thirds of the dorsum. This specimen represents a southern
range extension of 615 km and is also the first intertidal record of
the species (Millen. 1982).
• 17
Anisodoris nobilis (MacFarland, 1905)
Anisodoris nobilis is moderately common at Cape Arago, occurs at
all four coves, and can be found all year long at North Cove. I ob-
served specimens less than 10mm long in December and April. One March
specimen measured about 200mm in length. In the field A. nobilis was
found feeding on the yellow sponges Mycale macginitiei de Laubenfels,
1930, Zygherpe hyaloderma de Laubenfels, 1932, Tedania gurjanovae
Koltun, 1958, and Lissodendoryx firma (Lambe, 1895). Anisodoris
nobilis readily feeds on these sponges in the laboratory, and three
individuals also ate Ophlitaspongia pennata (Lambe, 1895) in the labora-
tory. Tedania gurjanovae and Ophlitaspongia pennata are new food
records for A. nobilis (McDonald and Nybakken, 1978; Bloom, 1981).
On 30 April 1982 I found one Anisodoris nobilis about 50mm long
under a boulder feeding on a Lissodendoryx firma individual covering
2 2
an area of 680cm (total boulder undersurface = 4900cm). Some of t1,e
sponge had already been grazed off the rock. On 21 August 1982 only a
few square centimeters of the sponge remained and no A. nobilis (nor
any other possible predators of the sponge) were present. Though I can
not rule out that other A. nobilis or other predators of ~. firma had
visited the rock, it is possible that the above A. nobilis ate all of
the missing sponge.
By area covered, Zygherpe hyaloderma is the most abundant of the
above yellow sponges at North Cove (pers. obs.). Mycale macginitiei,
which covers considerably less area (but is a thicker sponge) is next
most common. I conducted a crude experiment to try to determine which
18
of these two sponges is preferred by Anisodoris nobilis. Small pieces
2(0.25cm ) of each sponge were placed about 2cm apart and directly in
front of a crawling slug. I observed which sponge was contacted first
and which was ingested. A total of eight trials were made on two days,
using three slugs the first day and two the second. The slugs had been
starved for four days before the trials and ranged from 4 to 10cm in
length. The results (Table 2) suggest that Anisodoris nobilis prefers
Mycale over Zygherpe but will often eat the first sponge it contacts.
Further study of the food preferences of A. nobilis and the effects of
length of starvation, previous diet, and age would be interesting.
The ribbon of one egg mass laid by a 14cm long individual measured
2.7 x 40cm and contained about 2.1 million eggs. Larval development
data are presented in Table 1.
Aplysiopsis smithi (Marcus, 1961)
This sacoglossan occurred in a few high-intertidal pools between
South and Good Witch Coves. I examined these pools for Aplysiopsis
smithi monthly from June 1980 through July 1981. The sacoglossan and
its egg masses were abundant in late spring and early summer 1980, and,
with the exception of one specimen found in December 1980, disappeared
in September 1980 and did not reappear until May 1981. It was abundant
until at least July 1981, though not as common as in the previous year.
In these pools A. smithi feeds exclusively on the green algae Cladophora
sp. Greene (1970) reported southern California A. smithi feeding on
Cladophora trichotoma.
19
Table 2. Results of Anisodoris nobilis food preference experiment
Outcome of Trial Frequency
Sponge Contacted First1 Sponge Eaten
Zygherpe hyaloderma (Z) Z 3
Mycale macginitiei (M) M 0*
Z M 1
M Z 0*
Z & M Z 0
~t Z & M M 4
1
contact by anterior edge of mantle
* Mycale macginitiei was not contacted first in any of the trials
20
My observations of the egg masses and veligers match those of Greene
(1968). He observed white and yellow colored egg masses. I noticed
that laboratory specimens laid yellow egg masses at first. but later
egg masses were faint yellow to white. The newly hatched planktotrophic
veligers lack eyespots and possess a granular black pigment scattered on
the edge of the mantle that folds over the outer lip of the shell. Such
pigmentation is unique among the veligers observed in this study. Lar-
val development data are presented in Table 1.
Archidoris montereyensis (Cooper. 1863)
Archidoris montereyensis is fairly common at Cape Arago and occurs
year-round. Specimens ranged in length from 4 to 6Smm. Individuals less
than 10mm long were found from November to April. and individuals greater
than SOmm were observed in December. January. April. May. and July. Eggs
were observed in the field in May and July. I sometimes found A.
montereyensis stranded out of water feeding on Halichondria panicea
(Pallas. 1766) and on the massive and densely spiculate sponge Suberites
sp. One specimen. 10mm long. was found at Good Witch Cove embedded in a
soft. unidentified. orange. encrusting sponge.
Archidoris odhneri (MacFarland. 1966)
This species is quite common at Good Witch and Middle Coves but also
occasionally occurs at North and South Coves. With the exception of one
13mm long specimen found in June 1983 at North Cove. all specimens were
21
7 - 10cm long. Archidoris odhneri rarely occurred on sponges. Two
specimens, including the above 13mm individual, were on Hymeniacidon
ungodon de Laubenfels, 1932, and ate this sponge in the laboratory.
One 9cm long specimen, brownish-yellow in color (and the only ~. odhneri
I found that was not pure white), was found on a large Suberites sp.
individual of the same color - the sponge appeared to have been grazed.
Archidoris odhneri has not been reported feeding on either of these
sponges (McDonald and Nybakken, 1978; Bloom, 1981).
Berthella californica (Dall, 1900)
This pleurobranchomorph is common on the submerged, relatively
barren boulders at Good Witch Cove and also occurs occasionally at the
other three coves. Behrens (1980) considers Pleurobranchus denticulatus
to be synonymous with Berthella californica and gives Crescent City,
California as the northern range limit of B. californica. However,
Lambert (1976) reported Pleurobranchus denticulatus from Pearse Island,
British Columbia.
The egg mass of Berthella californica is a white ribbon, 3 - 4mm
wide, laid on edge in a loose spiral. The newly hatched veligers are
distinctive in possessing a dark, red wine colored patch of tissue on
the right side next to the anus, as well as a shell whose oldest portion
has a brown tinge (similar to the pigmentation on the veliger shells of
Hallaxa chani, but not as dark or extensive).
22
Cadlina luteomarginata MacFarland, 1966
This species is moderately common at all the coves of Cape Arago.
I occasionally found it feeding on the pink sponge Apysilla glacialis
(Dybowski, 1880). This sponge has previously been reported as the food
of ~. flavomaculata MacFarland, 1905, and ~. modesta, but not C.
luteomarginata (McDonald and Nybakken, 1978). One individual was found
feeding on a light grayish-tan colored!. glacialis individual, and a
number of C. luteomarginata starved in the laboratory fed on Halisarca
sp. One specimen, 23mm long at collection, has survived seven months
in the laboratory without any food except for one day of feeding on
Aplysilla glacialis one month after collection.
On 1 May 1982 I noted an Aplysilla glacialis individual covering an
area of 126cm2 on the underside of a North Cove boulder. The boulder
. 2
had 630cm of undersurface. I tagged the boulder to keep track of the
sponge. On 21 August 1982 one 27mm Cadlina luteomarginata and a 15mm
Cadlina modesta were observed feeding on this Aplysilla. They had eaten
18cm2 of the sponge, but the sponge had grown an approximately equal
amount since May. On 26 March 1983 both slugs were still present
(though I can not rule out that they were different individuals or that
additional individuals of Cadlina had visited the rock) and had eaten all
2but 4.5cm of the sponge. The C. luteomarginata measured 42mm and had
laid two egg masses (one recently laid; the larvae of the other had al-
ready hatched). The C. modesta measured 20mm. On 15 April 1983 both
dorids were gone and only a trace of Aplysilla remained.
.,.....'
·V
23
O'Donoghue and O'Donoghue (1922, p. 138) stated that the egg masses
of Cadlina luteomarginata " ...were not found so frequently as those of
Archidoris montereyensis and Diaulula sandiegensis although the animal
itself is quite common." and Costello (1983, p. 331) noted that " ... the
egg ribbons are less vertical than in ... other forms.". My observations
agree. I saw only two egg masses in the field, both in March 1983. The
egg mass ribbon slants toward the center of the tightly wound coil and
overlaps itself in the preceding turn. One egg mass had 5 turns and a
diameter of 16mm.
Cadlina modesta MacFarland, 1966
Before April 1982 I had only seen two Cadlina modesta at Cape Arago.
After April 1982 I found 15 specimens. All 17 specimens were observed
in spring and summer at North Cove. Two individuals were ·feeding on
Aplysilla glacialis and two on Halisarca sp., a previously unreported
sponge prey. One individual, 6mm long and found on Halisarca sp., sur-
vived in the laboratory at 80 - 160 C for 17.2 months. This specimen
was sporadically fed Halisarca sp. for the first 5 months, and grew to
20mm in length. It was then starved for 6 months. During the following
6 months it was again sporadically given Halisarca sp., and it ate a
2total of 13cm of the sponge (Halisarca sp. averages 2 to 3mm in thick-
ness). The specimen did not appear to eat any of the Halisarca sp.
present for the last month of its life, and it never laid eggs.
Concerning the color of the rhinophores of Cadlina modesta,
HacFarland (1966) wrote, lfRhinophores light, seldom dusky ..• ", and
24
Bertsch (1969) stated, "The color of the rhinophores varied from whitish
to dusky brown.". In laboratory specimens of Cadlina modesta the rhino-
phores changed from whitish or light yellow to brown with increasing
age.
The egg.mass of Cadlina modesta is a cream colored ribbon 2 - 3mm
high laid in a loose spiral of 1 - 3 turns. Mean egg mass area was
115.3mm2 (sd
n = 3), the "average" egg mass of Cadlina
252.0mm , n = 13 egg masses laid in laboratory by 3 spec-
2At a mean density of 180 eggs per mm of egg20mm long).
233 eggs/mm •
imens 15
mass (sd
modesta contains about 20,750 eggs.
Catriona columbiana (0 'Donoghue, 1922)
Catriona columbiana is frequent at Cape Arago and was usually on,
or near, the stolons of Tubularia marina (Torrey, 1902) on which it feeds.
C. columbiana appears to be most abundant in spring and summer, partic-
ularly at North and Middle Coves. Two color forms exist, one with
orange cephalic tentacles and one with white cephalic tentacles (both
forms have orange on the distal half of the rhinophores). I did not
observe any differences in the radula, mandibles, egg masses, and veli-
gers of these two forms.
This species lays small, sac to crescent-shaped egg masses (type
D of Hurst, 1967). There is one egg per capsule, and the capsules are
deposited in an irregular coil, 2 - 3 capsules wide, in the egg mass.
25
Crimora coneja Marcus, 1961
With the exception of a single specimen reported from "near
Humboldt Bay, Humboldt County, California" (McDonald, 1983), this deli-
cate and rare dorid was previously known only from the type locality of
Point Loma, San Diego County, California (Behrens, 1980; McDonald, 1983).
On August 29, 1981 Katheryn Young and Tom Wayne of O.I.M.B. collected
two individuals from under a boulder in the North Cove inner boulder
field. Both specimens were 16mm long. Since then I have observed seven
specimens, ranging in length from 14 to 19mm, at North Cove (one in
December 1981, one in April 1983, two in August 1983, and three in Sep-
tember 1983) and one 12mm specimen at Middle Cove in July 1983. These
eight specimens were on Hincksina minuscula on the undersides of boulders
approximately 0.3m in diameter.
Laboratory observations confirmed that Crimora coneja feeds on
Hincksina minuscula. One individual overnight ate almost every zooid in
2
a 1cm piece of bryozoan. The zooecia were empty and the frontal mem-
branes missing, indicating that Crimora uses its radula to rasp out en-
tire zooids (contrast with the feeding method of Adalaria sp.).
The egg mass of Crimora coneja is a thin ribbon laid flat (not on
edge like most dorids) in a spiral of 4 - 6 turns, and measures 9 - 12mm
in diameter. The ribbon is about 1mm wide, contains 1 - 2 layers of eggs
and lacks striations of any sort. In different egg masses the eggs vary
from white to pale orange in color. Because of its thinness and form,
the egg mass is difficult to discern when laid on bryozoan-encrusted
substrates.
26
Cuthona abronia (MacFarland, 1966)
This eolid can be common during the spring and summer at North and
Middle Coves. While occasionally seen crawling on submerged algae or on
the surface of calm tidepools, it usually occurs among minute, unidenti-
fied, thecate hydroids under boulders in areas subject to little accumu-
lation of silt and detritus (purple sea urchins are often in the vicinity).
In April 1982 I found five specimens and about 20 egg masses on the under-
side of a single small boulder.
Cuthona albocrusta (MacFarland, 1966)
Cuthona albocrusta occurred at Middle Cove (2 specimens in August
1980 and 4 in July 1983) and North Cove (5 in May 1980, 1 in July 1981,
and over 11 in July and August 1983). In August 1983 I found five spec-
imens clustered among minute, unidentified, unbranched, thecate hydroids
(probably of the family Campanulinidae). These hydroids were partially
covered by a fine, light greyish-tan colored silt - the eolids were quite
cryptic in this microhabitat.
Cuthona cocoachroma Williams and Gosliner, 1979
Three specimens of this rare eolid were seen at Middle Cove, one in
July 1980, one in June 1981, and one in June 1983. The range of Cuthona
cocoachroma is extended 255km from Trinidad Head, Humboldt County, Cali-
fornia (Jaeckle, 1981). I also found one specimen of ~. cocoachroma at
Cape Blanco (50km south of Cape Arago) in April 1982.
27
The egg mass of Cuthona cocoachroma is a white cord laid in a small
rosette.
Cuthona flavovulta (MacFarland, 1966)
I found seven specimens crawling on submerged algae or on the sur-
face of calm pools at Middle and North Coves in summer 1983. The range
of Cuthona flavovulta is thus extended from Palmer's Point, Humboldt
County, California (Jaeckle, 1981).
Cuthona fulgens (MacFarland, 1966)
Four specimens were found crawling on submerged algae or on the sur-
face of calm pools at North and Middle Coves in summer 1983. The range
of Cuthona fulgnes is extended from Duxbury Reef, California (Gosliner
and Williams, 1970).
Dendronotus frondosus (Ascanius, 1774)
I observed few Dendronotus frondosus at Cape Arago until June and
July 1983, when over 20 specimens were seen on a small unidentified species
of Obelia in the very low intertidal of Middle Cove. Dendronotus frondosus
can be abundant during the spring and summer, feeding on the much larger
and highly branched species of Obelia on the docks of the Charleston boat
basin (pers. obs.). All Cape Arago specimens were less than 2cm long, and
a number of individuals were on hydroids growing on the brown alga
Cystoseira. D. frondosus occurred in low numbers at all the coves of Cape
'.'~(
~
28
Arago.
Dendronotus subramosus MacFarland. 1966
I found only two specimens of Dendronotus subramosus at Cape Arago.
both at Middle Cove. One specimen. 4mm long. was under a small boulder.
and one 2mm specimen was on hydroid-covered Cystoseira.
Diaphana californica Dall, 1919
One specimen. with a 3mm long shell, of this minute Bullomorph was
collected from the North Cove inner boulder field ,in August 1981. I
found three more (shell lengths of 3.3mm, 3.0mm, and 2.1mm) in the same
location in September 1983. Much of the mantle and viscera is visible
through the thin translucent shell. The range of this species is ex-
tended 610km from Duxbury Reef, California (Gosliner and Williams, 1970).
The egg mass of Diaphana californica is a fragile and very extensible
cord attached to the substrate along its entire length. The cord of one
egg mass was laid straight, varied from 0.1 to 0.5mm in diameter, and
measured 20mm in length. Two other egg masses were C-shaped. with the
cord varying from 0.75 to 1.5mm in diameter; one of these was 7mm long,
the other 10mm.
29
Diaulula sandiegensis (Cooper, 1863)
This species is common at Cape Arago and is often seen under ledges
and boulders feeding on Haliclona sp. A of Smith and Carlton (1975, p.45).
Specimens ranged in size from 5 to 70mm. Specimens less than 15mm were
found in January, March, April, June, and July, and specimens over 50mm
long were found in May through July, and in October, and January. Small
to medium size individuals are often at the end of a "path" they have
eaten into Haliclona sp. and, owing to the resemblance of their dorsal
brown rings or spots to the oscula of the sponge, are quite cryptic.
Dirona albolineata Cockerell and Eliot, 1905
This species was abundant at North Cove during the latter part of
summer in 1980, 1981 and 1982. It was rare or absent in the other
seasons I looked. In 1983 I did not see any until early September, when
only two were found. Dirona albolineata is usually crawling on algae
and rocks in pools along with Janolus fuscus and Triopha catalinae.
Discodoris heathi MacFarland, 1905
I found five specimens ranging in size from 7 to 90mm during the
summer months at North Cove, and one 20mm individual in August at Middle
Cove. An 11mm specimen was embedded in Mycale macginitiei under a boulder
and ate this sponge in the laboratory. A 60mm slug are a 30mm diameter
Mycale macginitiei individual overnight. This is a new food record for
Discodoris heathi.
30
Discodoris heathi lays large yellow egg masses in the typical dorid
form.
Doto amyra Marcus, 1961
I observed this species only at Middle Cove: one in July 1980, five
in June 1981, and 22 (with egg masses) in May and July 1983.
Despite the taxonomic confusion surrounding Eastern Pacific Doto
species (Marcus, 1961 described four new species, but Behrens, 1980 and
McDonald and Nybakken, 1980 only list two of those), I am calling this
species Doto amyra after McDonald and Nybakken (1980). With the excep-
tion of one, all the specimens I examined matched their description and
photograph of Doto amyra (Marcus's original description mentions little
about the living animal). The cerata cores varied from light yellow to.
light orange-brown; the gonads were yellow, and the cerata tubercles
were translucent white and contained slightly opaque white grains (these
grains are larger and less dense than the opaque white grains present in
the distal parts of the rhinophores and their sheaths). The exceptional
specimen mentioned above, while possessing all the above characteristics,
also possessed a subcutaneous black pigment in the body similar to that
in the body of Data kya. However, this slug laid eggs identical to those
of the other Doto amyra, and, as seen below, the eggs of Doto amyra are
very different from those of Doto kya.
Most of the Data amyra, and all of the egg masses, were on colonies
of the thecate hydroid Abietinaria sp., a previously reported prey of
Data amyra (Beeman and Williams, 1980). Slugs occurred on both the
31
stolons and upright portions of the hydroid. Egg masses were usually
attached to the bases of the colonies.
Doto amyra feeds on Abietinaria sp. by rasping a circular hole in
the perisarc with its radula and then sucking out the hydroid tissues
by means of muscular contractions of its esophagus (pers. obs.). One
5mm long slug rasped a hole 32 in diameter in the perisarc.
Doto amyra lays yellowish egg masses that are laterally flattened,
slightly crescent-shaped with rounded ends, and laid on edge. The thick
jelly attachment sheet is translucent white with parallel white stria-
tions; the rest of the egg mass jelly is clear. Egg masses measure up
to 1.5mm high by 4mm long and derive their yellow color from the yellow
eggs.
The larvae of Doto amyra hatch out as crawling veligers possessing
large eyespots, a large foot, a small velum, and poor swimming abilities.
In the presence of Abietinaria sp., they metamorphose into juvenile
slugs within a few days after hatching (pers. obs.). Doto amyra is the
first eastern Pacific nudibranch known to produce lecithotropic larvae
(type 2 development of Thompson, 1967) (Hurst, 1967; Thompson, 1967;
Bonar, 1978; present study). I examine this development more closely
elsewhere (ms in preparation).
Doto kya Marcus, 1961
In May and June 1980 I found four specimens at North Cove. Two of
these were among Plumularia sp. and a short unidentified hydroid of the
family Campanulinidae - both hydro ids were growing on the perennial
32
portion of the brown alga Cystoseira. Three more were seen at Middle
Cove in July 1983. All specimens match the photograph of Data kya in
Behrens (1980).
The white egg masses of Data kya are laterally flattened (more
flattened than the egg masses of Data amyra), slightly wavy or folded
crescents to semi-circles laid on edge and measure up to 3mm in length.
Eubranchus olivaceus (OIDonoghue, 1922)
Two specimens, 6mm and 8mm long, were found at North Cove in June
and July 1983. The radula from the latter one has 42 rows of teeth and
does not taper. As Marcus (1961, p. 49) noted, the nontapering radula
is at present the major anatomical character distinguishing E.
olivaceus from E. rustyus.
Eubranchus rustyus (Marcus, 1961)
I found a few Eubranchus rustyus in the summer months at North and
Middle Coves. Six specimens 0.5 - 5mm long occurred with egg masses on
Plumularia sp. at Middle Cove in July 1983. !. rustyus eats this hy-
droid in the laboratory (pers. obs.). The radula from a 6mm long spec-
imen has 57 rows of teeth and tapers distinctly.
33
Flabellina trilineata (0 'Donoghue, 1921)
Flabellina trilineata is the most abundant eolid at Cape Arago and
occurs at all four coves. It is commonly found feeding on Tubularia
marina, an abundant hydroid at Cape Arago. Both species appear to be
most abundant during the spring. I have observed F. trilineata feeding
on Eudendrium californicum Torrey, 1902 in California (and McDonald and
Nybakken (1978) report it feeding on Eudendrium sp.). Although large
Eudendrium californicum colonies occur at Middle Cove, often in close
proximity to !. trilineata and Tubularia marina, I never observed the
eolid on them. This suggests that F. trilineata prefers Tubularia
marina to Eudendrium californicum.
Many individuals of F. trilineata lacked orange pigment on the
rhinophores and cephalic tentacles. MacFarland (1966, p. 321) also
noted this variability in color pattern.
Hallaxa chani Gosliner and Williams, 1975
Since first reporting two specimens of Hallaxa chani from North
Cove, Cape Arago (Goddard, 1981), I have seen over 70 individuals in
the North Cove inner boulder field, and as many as 14 specimens on a
single low tide. ~. chani is usually on or near its sponge prey
Halisarca sp. underneath mid- to low- intertidal boulders.
In the laboratory Hallaxa chani of all sizes readily feed on
Halisarca sp. and do not feed on the white colonial tunicate (either
Didemnum carnulentum Ritter and Forsyth, 1917 or Trididemnum opacum
34
(Ritter, 1907) that is common under North Cove boulders and was previ-
ously suspected to be eaten by ~. chani (see Goddard, 1981). I have
never observed~. chani feeding on any other organisms.
Hallaxa chani blends in well on Halisarca sp. Both organisms are
light to yellowish-tan in color, and the reddish-brown flecks and sub-
cutaneous dark spots on H. chani match the dark spots on Halisarca sp.
(The "dark spots" on Halisarca sp. are caused by the sponge structure
rather than pigmentation. They appear to be associated with the water
canal system.) Moreover, when feeding, ~. chani tends to spread out its
semi-translucent dorsum, thus taking on some of the sponge color and
also making the thin edge of the dorsum difficult to discern. Small
H. chani are very cryptic.
Observations indicate that Hallaxa chani grows rapidly for a dorid
of its size, reaches maturity in a few months, and lives approximately
six months. One individual, 5mm long (wet weight of 20mg) at collection,
kept in 100 C water, and given Halisarca sp. every few weeks, grew to a
wet weight of 360mg in 44 days, and laid an egg mass 44 days after col-
lection. It weighed 121mg on day 132, and was moribound after 152 days.
Four other specimens of similar initial weight (including one that was
kept isolated and never laid eggs - this individual reached a length of
28mm and a weight of 957mg) lived 150 days or less under similar con-
ditions.
The egg mass of Hallaxa chani is a cream colored ribbon 2 - 3mm
high laid in a loose spiral of 1 - 3 turns. The hatching veligers lack
eyespots and possess type 1 shells whose oldest portion is a translucent
35
brown color. Specimens of H. chani less than 5mm long occurred in all
seasons, and egg masses were found in all seasons except winter, in-
dicating that reproduction occurs most of the year.
Hermaea vancouverensis O'Donoghue, 1924
I found four specimens, 6 - 8mm long, of this sacoglossan on brown
algae in the North Cove inner boulder field in June 1981.
Hermissenda crassicornis (Eschscholtz, 1831)
Hermissenda crassicornis was not very common at Cape Arago. In
June 1981 I found over 20 specimens at Middle Cove, but on other occa-
sions never more than six. Interestingly,~. crassicornis is abundant
on the docks of the Charleston boat basin during spring and summer.
Most of the H. crassicornis at Cape Arago and the boat basin are the
variety possessing a bluish-white stripe on the cerata (see Behrens,
1980, p. 93, lower photograph). H. crassicornis occurs in all four
coves.
Janolus fuscus O'Donoghue, 1924
Gosliner (1982) recently reinstated Janolus fuscus as a distinct
species from the more southerly Janolus (Antiopella) barbarensis
(Cooper, 1863). Cape Arago Janolus are all Janolus fuscus and, the
Antiopella barbarensis reported from Oregon by Sphon (1972) were un-
doubtedly also~. fuscus.
36
Janolus fuscus occurred from April to October at North Cove only.
During August and September it is one of the most abundant and conspicu-
ous nudibranchs at North Cove. It is usually found crawling on rocks
or on the algae Sargassum, Egregia, and Phyllospadix in the large pools
of the inner boulder field where it searches for the arborescent bryo-
zoans upon which it feeds (McDonald and Nybakken, 1978; pers. obs.).
Laila cockerelli ~1acFarland, 1905
Laila cockerelli was uncommon at Cape Arago until spring and
summer 1983 when I found a total of 20 specimens at North and Middle
Coves. It also occurs at South and Good Witch Coves. A number of in-
dividuals were observed on the light orange bryozoan Hincksina velata
(Hincks, 1881) and ate this bryozoan in the laboratory. Laila
cockerelli has been reported feeding on Hincksina velata in California
(McDonald and Nybakken, 1978).
My observations of the pink colored egg mass of Laila cockerelli
generally match those of O'Donoghue (1922). However, he described it
as a fI ••• slightly flattened string •.•wound in a close, tight-fitting
spiral. fI • Egg masses I observed were a ribbon laid flat in a close
spiral. It is very similar in morphology to the egg mass of Crimora
coneja. One egg mass had 4.5 turns, a diameter of 15mm, and a ribbon
whose width varied from 1.5 to 20.mm.
37
Onchidoris muricata (Muller, 1776)
This small dorid is sporadically common at North Cove. It usually
occurs under boulders on Eurystomella bilabiata (Hincks, 1884), an
abundant bryozoan which it eats in the laboratory (pers. obs.).
Onchidoris muricata that have been feeding on this bryozoan possess a
deep red colored digestive gland visible through the foot. I also found
Q. muricata on Microporella cribosa (Osburn, 1952) and Hincksina
minuscula but did not confirm feeding on these two species.
Onchidoris muricata can be difficult to distinguish from Adalaria
sp. in the field. However, O. muricata is usually shorter, rounder,
and has bulbous, fairly smooth dorsal papillae. The pointed spicules
in the papillae of O. muricata barely protrude above the surface of the
papillae; those of Adalaria sp. protrude very far.
Hurst (1967) described the egg mass of Onchidoris muricata. Like
many other dorids, O. muricata sometimes only lays a small portion of
an egg coil (pers. obs.).
Onchidoris sp. (cf. Onchidoris hystricina)
This species is referred to as Onchidoris hystricina by Behrens
(1980, pp. 66 and 67), McDonald and Nybakken (1980, pp. 44 and 45), and
Beeman and Williams (1980, p. 328). However, Onchidoris sp. disagrees
with Bergh's 1878 and 1880 descriptions of Q. hystricina, as well as
Marcus's (1961) description of Q. hystricina. The dorsal papillae,
gills, and radula are very different (Sandra Millen, pers. comm.; pers.
obs.). It appears to be undescribed.
38
Onchidoris sp. was observed at North Cove in August and September
of 1981, 1982, and 1983. It was common in these months all three years.
The white egg mass of Onchidoris sp. is a cord, 0.75 - 1.0mm in
diameter, laid in a disorderly spiral of 1 - 4 turns measuring up to
5mm in diameter.
Placida dendritica (Alder and Hancock, 1843)
I found this species feeding on Codium fragile in pools between
South and Good Witch Coves. Behrens (1980) reports San Francisco Bay
as the northern limit of this species, but Lambert (1976) found it on
the northern tip of Vancouver Island, British Columbia.
Polycera atra MacFarland, 1905
Three specimens were observed in September 1983 at North Cove.
Polycera atra occurred by the hundreds feeding on arborescent bryozoans
in the Charleston boat basin in June 1983, but repeated observation in
mid-July only turned up a single specimen. The range of Polycera atra
is extended from Humboldt Bay, California (Jaeckle, 1981).
Precuthona divae Marcus, 1961
This eolid occurred in low numbers at North and Middle Coves in the
spring and summer. One specimen from Middle Cove was 32mm long. I have
also found Precuthona divae at Cape Blanco (50km south) feeding on the
:)
pink colonies of Hydractinia sp.
39
The egg mass of P. divae is a round,
hemispherical-shaped rosette. Robilliard (1971) reported egg masses of
~. divae from San Juan Island, Washington as being white; those at my
study sites were pink.
Rostanga pulchra MacFarland, 1905
Rostanga pulchra is abundant at Cape Arago and occurs with its egg
masses throughout the year. I observed it feeding on Ophlitaspongia
pennata and also found it (and its eggs) on Antho lithophoenix (de
Laubenfels, 1927) and Hymedesmia sp. A (of Smith and Carlton, 1975,
p. 51). I also found~. pulchra close to, but not on, Plocamia
karykina de Laubenfels, 1927 and Axocielita originalis (de Laubenfels,
1930). R. pulchra has previously been reported feeding on, or occurring
on, all of the above sponges except for Hymedesmia sp. A (McDonald and
Nybakken, 1978).
Triopha catalinae (Cooper, 1863)
One of the most common dorids at Cape Arago, Triopha catalinae
occurs year-round but is most abundant during summer and fall, espec-
ially at North Cove. Individuals ranging in size from less than 10mm
to 70 or 80mm can be found in nearly any month; this suggests a long
breeding season and a probable lack of synchrony of reproduction among
individuals. I've never seen!. catalinae egg masses in the field.
Egg masses laid in aquaria are large, pinkish-white, coiled ribbons
)
40
laid on edge.
At Cape Arago Triopha catalinae feeds on unidentified species of
arborescent and encrusting bryozoans. Small individuals are often
found on bryozoans on the undersides of boulders, and large individuals
are usually out in the open, crawling on submerged algae and rocks.
Triopha maculata MacFarland, 1905
I found five orange specimens during summer 1983 at North Cove.
All were 10 - 20mm long, and three were observed on bryozoans underneath
boulders.
Tritonia festiva (Stearns, 1873)
Tritonia festiva occurs at all four coves but is most common at
Middle and Good Witch Coves. It usually occurs on or near a white
Alcyonacean octocoral upon which it feeds. Sowell (1949) also reported
finding!. festiva "on or near" this octocoral but did not confirm
feeding. The octocoral is in the form of low, rounded colonies up to
15mm in diameter and is undescribed (Dr. F.M. Bayer, pers. comm.).
Large aggregations of fairly evenly spaced colonies are common under
wave-exposed, low-intertidal ledges at Cape Arago. Tritonia festiva
has been reported to feed on octocorals of the orders Stolonifera,
Gorgonacea, and Pennatulacea, but not Alcyonacea (McDonald and
Nybakken, 1978).
)The feeding process is remarkable. Upon contacting an expanded
41
colony with the very sensitive, slender processes on its frontal veil,
the slug immediately stops crawling and raises the anterior half of its
body off the substrate, reaches over the edge of the colony without
contacting it, and then quickly comes down on the polyps while extend-
ing its buccal mass and jaws. A few polyps are bitten off, and the
rest of the colony contracts. Extension of the buccal mass and the
actual biting occur very rapidly. Tritonia festiva will not attack
contracted colonies (probably because it cannot penetrate the tough
and densely spiculate coenenchyme), and in all of the instances I've
observed, contact of a colony by Tritonia's frontal veil never resulted
in polyp contraction.
I also found Tritonia festiva next to Clavularia sp., a stoloniferan
octocoral which I observed !. 'festiva eating in the laboratory and which
has previously been reported as a prey item of T. festiva (McDonald and
Nybakken, 1978). T. festiva from Cape Arago also attacked specimens of
Gersemia rubiformis (Pallas) collected from Cape Blanco and an unident-
ified pink gorgonian dredged offshore by local fishermen. T. festiva
has not previously been reported feeding on Gersemia rubiformis.
The white egg mass of Tritonia festiva is a flattened cord laid in
a close spiral and attached to the substrate by a thin, egg-free jelly
sheet (type B egg mass of Hurst, 1967). The cord is somewhat convoluted,
giving the egg mass a rosette appearance. Dimensions are: egg mass
diameter, 10 - 20mm; height, 1mm; cord diameter, 0.5mm. The egg mass
is delicate, and the eggs are not embedded in a jelly matrix.
)
42
DISCUSSION
Life Cycles
Most of the dorid nudibranchs, and all of the eudoridaceans, whose
life cycles have been studied have been shown to possess annual life
cycles (Clark, 1975; Eyster and Stancyk, 1981; Miller, 1962; Potts,
1970; Swennen, 1961; Thompson, 1964, 1976; Todd, 1978, 1979). Dorids
known or suspected to possess subannual life cycles are generally smal-
ler, bryozoan-feeding members of the families Corambidae, Goniodorididae,
Onchidorididae (the species of Onchidoris thus far studied, though, are
annuals), and Polyceridae (Clark, 1975; Miller, 1962; Perron and Turner,
1977; Swennen, 1961).
Data presented above on the lifespan of Hallaxa chani strongly
suggest that this eudoridacean is subannual. Combining the observations
on lifespan, egg-laying, and larval development, and assuming a 1 month
planktonic existence and 1 or 2 months for the juvenile to reach a
length of 5mm, generation time appears to be about 4 or 5 months at
100 C. It could be shorter at higher temperatures.
) 43
The relatively rapid growth and short generation time of Hallaxa
chani appear to be adaptations for exploiting its sponge prey Halisarca
sp. A species of Halisarca from New Zealand grows rapidly compared to
most other sponges and has a generation time of 4 - 5 months (Bergquist,
1978). I observed one group of Halisarca sp. individuals under a
2 2
marked boulder at Cape Arago increase in area from 8cm to 16cm between
6/29/83 and 9/7/83 (70 days), and I can not rule out the possibility
that they were preyed upon during this period and thus actually grew
more. The North Cove Halisarca sp. population is composed of widely
distributed individuals averaging only a few square centimeters in area
(pers. obs.). Laboratory and field observations indicate that Hallaxa
chani are capable of eating these individuals in a matter of days or
weeks. Instead of relying on energetically expensive, and thus growth-
slowing, skeletal and chemical defenses against predators like many
other sponges, natural selection appears to have favored the fugitive
tactics of rapid growth, high fecundity, and larval dispersal in
Halisarca as a means of escaping overpredation. These same life cycle
characteristics appear to have been selected for in Hallaxa chani,
enabling them to reproduce and find new Halisarca sp. individuals. The
largest Halisarca sp. I found at Cape Arago occurred under boulders at
Middle Cove, where I have never observed Hallaxa chani. Occasional
large Halisarca sp., which have apparently escaped predation by H. chani
(at least temporarily) also occur at North Cove.
Observations on the longevity of Cadlina luteomarginata and
Cadlina modesta suggest that these dorids live at least a year, and
)
44
thus possess life cycles more similar to those known for other eudo-
ridaceans. One Cadlina modesta survived a period of starvation longer
(and at higher temperatures) than the entire lifespan of regularly fed
Hallaxa chani. Although this Cadlina modesta never laid eggs, obser-
vations by Thompson (1961), Todd (1978), and Eyster (1981), as well as
the above observations on one Hallaxa chani that never laid eggs, all
indicate that lack of reproduction can result in larger size, but does
not significantly affect lifespan.
Development
Data on the larval development of Cape Arago opisthobranchs are sum-
marized in Table 1. Aplysiopsis smithi, Onchidoris muricata, and Triopha
catalinae are the only species in this Table whose development has prev-
iously been examined (Hurst, 1967; Greene, 1968; Beeman and Williams,
1980).
The development times, sizes of eggs and veligers, and the produc-
tion of veligers that lack a propodium, usually lack eyespots, and
possess a mantle fold that attaches intermittently to the shell lip all
indicate that, with the exception of Doto amyra, every species in Table
1 produces planktotrophic veliger larvae (type 1 development of Thompson,
1967) (Thompson, 1967; 1976). As mentioned previously, Data amyra pro-
duces lecithotrophic veligers (type 2 development).
Of the 20 species in Table 1 that produce planktotrophic larvae,
four (20%) produce veligers possessing eyespots at hatching. This is
) 45
rather high considering that the veligers of only one of the 30 North-
eastern Pacific opisthobranchs studied by Hurst (1967) have eyespots at
hatching, and the statement by Thompson (1976) that hatching plankto-
trophic veligers usually lack eyespots. Planktotrophic veligers develop
eyespots before metamorphosis, and species with lecithotrophic or direct
development always possess eyespots at hatching (Thompson, 1976). As
Bonar (1978, p. 187) states, "The eyes ...usually develop rather late in
embryogenesis, and along with the appearance of an enlarged propodium
signal the approach of metamorphic competence." It thus seems likely
that the above four species will be found to possess relatively short
obligatory planktonic stages compared to many other species with plankto-
trophic larvae.
The data in Table 1 generally support Thompson's (1976, p. 86) gen-
eralization that "Within development-type 1, species with the largest
eggs have a longer embryonic period, and, moreover, give rise to larger
veliger larvae."
Food and Competition
While most nudibranch species are known to eat a number of prey
species (Thompson, 1964, 1976; McDonald and Nybakken, 1978), a few
species appear to be monophagous over their entire ranges. Of the
species found at Cape Arago, only Adalaria sp., Ancula pacifica,
Hallaxa chani, Laila cockerelli, and Precuthona divae, so far as is
known, fit into this latter category (McDonald and Nybakken, 1978;
)Beeman and Williams, 1980; Goddard, 1981; present study). Crimora
46
coneja apparently feeds only on Hincksina minuscula at Cape Arago, but
it is doubtful that this latter species occurs in San Diego County,
California, one of the other locations where ~. coneja occurs (Osburn,
1950). The generalist species at Cape Arago appear to include
Anisodoris nobilis, Dirona albolineata, Hermissenda crassicornis,
Rostanga pulchra, and Triopha catalinae (Robilliard, 1971a; Nybakken
and Eastman, 1977; McDonald and Nybakken, 1978; Beeman and Williams,
1980; Bloom, 1981; present study). I suspect that most nudibranch
species will be found to eat relatively few prey species belonging to
a few genera. Data obtained in this study on the prey of Cape Arago
nudibranchs are summarized in Table 3. These data are incomplete. With
the possible exceptions of Cadlina modesta and Hallaxa chani, more data
are needed on the prey of all Cape Arago nudibranchs.
The alcyonacean octocoral prey of Tritonia festiva often occurs in
large aggregations of fairly evenly spaced colonies, and, as mentioned
earlier, T. festiva will not attack colonies with contracted polyps.
How long do the polyps remain contracted after an attack by!. festiva?
~fuat sort of foraging path do!. festiva make through aggregations of
colonies? Feeding interference between individuals of T. festiva could
be considerable at higher densities of !. festiva (i.e., at high densi-
ties of T. festiva most of the octocoral polyps would be contracted).
In this regard it is interesting to note that T. festiva are aggressive
towards each other in the laboratory and often take large bites out of
each other. In one instance I placed two newly collected individuals
)Table 3.
nudibranch species
Adalaria sp.
Aeolidia papillosa
Ancula pacifica
Anisodoris nobilis
Prey of Cape Arago opisthobranchs
prey
Hincksina minuscula*
Epiactis prolifera
among Barentsia sp.
Mycale macginitiei
Zygherpe hyaloderma
Lissodendoryx firma
Tedania gurjanovae*
Ophlitaspongia pennata (L)*
47
Archidoris montereyensis
Archidoris odhneri
Cadlina luteomarginata
Cadlina modesta
Catriona columbiana
Crimora coneja
Cuthona abronia
Cuthona albocrusta
Dendronotus frondosus
Diaulula sandiegensis
Discodoris heathi
Halichondria panicea
Suberites sp.
unidentified orange
encrusting sponge
Hymeniacidon ungodon*
on Suberites sp.
Aplysilla glacialis
Halisarca sp. (L)*
Aplysilla glacialis
Halisarca sp.*
Tubularia marina
Hincksina minuscula*
among small thecate hydro ids
among small thecate hydro ids
Obelia sp.
Haliclona sp. A
Mycale macginitiei*
Abietinaria sp.
among Plumularia sp. and
small thecate hydro ids
)Eubranchus rustyus
Flabellina trilineata
Hallaxa chani
Janolus fuscus
Laila cockerelli
Onchidoris muricata
Polycera atra
Precuthona divae
Rostanga pulchra
Triopha catalinae
Triopha maculata
Tritonia festiva
sacoglossan species
Aplysiopsis smithi
Placida dendritica
* new food record
Table 3 (cont.)
Plumularia sp.
Tubularia marina
Halisarca sp.
arborescent bryozoans
Hincksina velata
Eurystomella bilabiata*
on Hincksina minuscula
on Microporella cribosa
arborescent bryozoans
Hydractinia sp.
Ophlitaspongia pennata
on Aotho lithophoenix
on Hymedesmia sp. A
near Plocamia karykina
near Axocielita originalis
arborescent bryozoans
arborescent and encrusting
bryozoans
undescribed alcyonacean
octocoral*
Clavularia sp.
Gersemia rubiformis (L)
Cladophora sp.
Codium Fragile
48
(L) opisthobranch species not found associated with their
prey in field, but ingestion of prey observed in laboratory
) 49
(20 and 35mm long) together in 500ml of water. After one day of captiv-
ity the larger ate the smaller specimen. Does aggressive behavior occur
in the wild as a mechanism for reducing slug density? and if so, how
does reproductive behavior fit in? How widespread is cannibalism? Can
T. festiva detect conspecific mucus trails? A study of foraging behavior
(for both food and mates) in this species would be fascinating.
Large numbers of Triopha catalinae, Janolus fuscus, and Dirona
albolineata are found together in the North Cove inner boulder field dur-
ing late summer and early fall. T. catalinae and J. fuscus feed on ar-
borescent bryozoans (Nybakken and Eastman, 1977; McDonald and Nybakken,
1978; pers. obs.), and Q. albolineata eats a wide variety of prey in-
eluding bryozoans (Robilliard, 1971a). It seems likely that some comp-
etition for food occurs between these species during periods of co-
occurrence.
When Janolus fuscus are crowded in the laboratory they often bite
each other, sometimes tearing off and ingesting cerata. This aggressive
behavior may be a mechanism for maintaining a certain amount of space,
and thus food, per individual. Study of the relationship between food
supply, density and age of ~. fuscus and the frequency of aggressive
and reproductive interactions should prove interesting.
Triopha catalinae are rarely found in close proximity to one
another (Nybakken and Eastman, 1977, p. 282; pers. obs.), suggesting
that aggressive interactions may also occur between individuals of this
species. The feeding method of !. catalinae (in which whole branches of
arborescent bryozoans are ripped off and ingested), and the laboratory
) 50
observation of a large I. catalinae attacking and taking a sizable bite
out of a Laila cockerelli (pers. obs.) indicate that T. catalinae are
physically capable of such aggression. Furthermore, does any inter-
specific aggression or predation occur between T. catalinae, Janolus
fuscus, and Dirona albolineata?
Ranges
The range extensions reported above for Cuthona flavovulta, ~.
fulgens, and Polycera atra, and the occurrence in spring and summer 1983
of the form of Ancula pacifica common in California may be related to
events associated with the strong El Nino of 1982-83 (Philander, 1983).
These events have included above normal ocean temperatures off the coast
of North America (Dr. K.T. Briggs, Univ. of Calif. at Santa Cruz, pers.
comm.; A. McGee, Oregon Dept. Fish and Wildlife, pers. comm.) and prob-
ably a reversal of the usually south-moving California current (Chelton,
1981), as well as an intensification of the nearshore, north-moving
Davidson current that occurs in late fall and early winter (Bolin and
Abbott, 1963; Schwartzlose and Reid, 1972). If the above species have
been transported north (as veligers) with these anomalous events, their
occurrence at Cape Arago may be brief. On the other hand, they may occur
relatively consistently, but in low numbers, at Cape Arago and may have
been previously overlooked - this appears to be the case for Crimora
coneja, Cuthona cocoachroma, and Diaphana californica, all of which were
found at Cape Arago before the onset of the above anomalous conditions.
))
51
I would like to recommend that dates of observation always be given
with range extensions and reports of unusual occurrence. For with in-
creasing monitoring and understanding of coastal hydrographic conditions,
it may become possible to explain better the occurrence of many species
at the edges of their ranges, or to explain why a species appears in an
area for a time and then disappears for long periods. For example, is
it possible that the Hopkinsia rosacea reported from Oregon by Steinberg
(1963b) (see below) were carried north (as veligers) from California
with the warm waters and currents associated with the intense El Nino of
the late 1950's? Mention of the date of observation would have helped
evaluate such a possibility. It is interesting that Eurystomella
bilabiata, the only known prey of ~. rosacea, is abundant at Cape Arago
year-round, but ~. rosacea is usually absent (pers. obs.).
The known range of Crimora coneja is puzzling. Despite extensive
field observation of nudibranchs in central California, only one specimen
has been reported between San Diego and Cape Arago (McDonald, 1983).
The Effects of Nudibranch Predation on the Diversity of the Encrusting
Animal Community at Cape Arago
Low-light habitats at Cape Arago (crevices, caves, and the under-
surfaces of boulders and ledges) support a diverse encrusting community
composed primarily of sponges, bryozoans, colonial tunicates, and
cnidarians. The amount of free space varies depending, in part, on the
habitat and degree of physical disturbance. For example, the undersurfaces
))
52
of low intertidal ledges and stable boulders exposed to little sedimen-
tation tend to have little free space, whereas the undersurfaces of
boulders exposed to seasonal sedimentation and overturning by waves tend
to possess large amounts of free space (pers. obs.).
As in any community, part of the encrusting animal diversity at
Cape Arago can be explained by the spatial complexity (heterogeneity),
coupled with niche diversification and the evolution of habitat selection.
However, the coexistence of large numbers of species on relatively uni-
form surfaces suggests that other factors must be involved in regulating
species diversity. Factors that have been implicated in affecting the
diversity of other communities and which are probably important at Cape
Arago include: predation and disease, fluctuations in the physical and
biotic environments, physical disturbance in the form of sedimentation,
boulder-overturning by surf, and erosion (boring clams playa major role
in erosion and production of spatial complexity at Cape Arago), and the
existence of competitive networks among the encrusting species (Connell,
1972, 1978; Dayton, 1971; Huston, 1979; Hutchinson, 1961; Jackson and
Buss, 1975; Paine, 1974; Sousa, 1979). The first three factors can
maintain relatively high levels of diversity by preventing competitive
equilibrium (at which competitively inferior species are excluded from
the community) from being reached. Of course, at high enough levels,
these same factors can keep diversity low. The existence of complex
competitive networks can increase the time necessary for competitive
exclusion to occur (relative to the time required if only competitive
hierarchies exist) or mean that major competitive dominants just do not
))
53
exist in the community (Jackson and Buss, 1975; Jackson, 1979, 1981).
As Connell (1978) and Huston (1979) have discussed, a number of these
factors probably operate simultaneously in any particular community,
with the relative importance of each factor varying in different com-
munities. The observed diversity in a community is thus the result of
a "dynamic equilibrium" between the growth rates of the component pop-
ulations and the rates of the above mentioned factors (Huston, 1979).
Nudibranchs, which are known to be important predators in some en-
crusting communities (Bloom, 1981; Clark, 1975; Dayton et. al., 1974;
Ryland, 1970; Thompson, 1964; and, on the basis of abundance, Nybakken,
1974, 1978), appear to be among the most abundant and important preda-
tors of encrusting organisms at Cape Arago (pers. obs.). Other signif-
icant predators of these organisms at Cape Arago include prosobranchs
such as Diodora aspera (Rathke, 1833) and members of the family
Lamellaridae, and probably various chitons, asteroids, and fish (Morris
et. al., 1980, pers. obs.). Certain flatworms, polychaetes, crustaceans,
and pycnogonids are known to eat encrusting animals (Morris et. al.,
1980) and may also be important - especially with regard to predation on
newly settled organisms.
Not knowing which encrusting species are competitively dominant at
Cape Arago, I can not say to what extent nudibranchs prey on such species.
But, because nudibranchs can eat large amounts of sessile organisms (see
data on Anisodoris nobilis, Cadlina luteomarginata, ~. modesta,
Discodoris heathi, and Hallaxa chani), and eat such a wide variety of
prey, many of which are among the more abundant species (pers. obs.),
Some examples of their effects
)
54
they probably significantly affect the competitive relationships in the
1
encrusting community at Cape Arago
follow.
Other than reducing the abundance of their prey, the most obvious
result of nudibranch predation on encrusting communities is the creation
of free space available for larval recruitment or intrusion by surround-
ing organisms. By consuming entire individuals or colonies, nudibranchs
could also alter the species composition under a boulder or ledge.
Overgrowth is one of the primary mechanisms of competition between
encrusting organisms (Jackson, 1979). In some cases nudibranchs (and
other predators) could undo overgrowth events between encrusting species
by preying on the overgrowing species. This probably only applies to
sessile organisms which can be completely grazed off the overgrown
species (i.e., certain sponges, tunicates, and perhaps fleshy bryozoans)~
The sponge Halisarca sp. frequently overgrows the bryozoan Eurystomella
bilabiata. I have also seen it overgrowing the alcyonacean octocoral
prey of Tritonia festiva. On a number of occasions I collected E.
1Though I do not have good estimates of nudibranch abundance at.Cape
Arago, I can say that 2 to 3 hours 2f searching (by an experienced
observer) in an area of about 3000m in the North Cove inner boulder
field will turn up about 50 to 100 individuals of 10 to 15 species of
nudibranchs. Two factors make this a gross underestimate of actual
abundance: 1) only a part of the area is occupied by encrusting
animals - the rest is either dominated by algae or is barren. 2) not
all ledges and boulder undersurfaces are examined. Nudibranch abundance
at North Cove appears comparable to that of central California, but the
number of species is lower (pers. obs.).
55
bilabiata overgrown by Halisarca sp. to feed. the sponge to laboratory
Hallaxa chani. The dorids grazed the sponge cleanly off the bryozoan,
)
and within a day or two the bryozoan lophophores were extended and feed-
ing. Of course, the viability of the overgrown organism will depend on
how long and how extensively it has been overgrown and on its sensitiv-
ity to any allelopathic substances made by the overgrowing organism.
The large individual of Aplysilla glacialis I observed eaten by Cadlina
luteomarginata and~. modesta (see notes on~. luteomarginata had
partially overgrown some Cliona celata Grant, 1826. The Cliona celata
appeared healthy after the Aplysilla had been grazed away. This is not
too surprising, however, considering the shell-boring abilities of Cliona,
and it also suggests that Aplysilla glacialis has little or no allelo-
pathic effect on Cliona celata.
Partial predation, which results in decreased feeding and reproduc-
tive abilities of the grazed organism, and can also expose it to settle-
ment by possibly superior competitors (Jackson and Palumbi, 1979), is
probably widespread. It is inevitable in spatially complex microhabitats
where predators can not reach all of their prey. Moreover, how many
predators, given the chance, actually graze all of a sponge or every
bryozoan zooid? Some predators are just not capable of consuming entire
colonies (e.g. Tritonia festiva feeding on alcyonacean octocorals, pos-
sibly Ancula pacifica on Barentsia sp., and probably many hydroid-eating
eolids which consume the hydranths, but not the stalks and stolons from
which hydranths can regenerate). An important question is, how much can
a sessile organism lose to predation and still survive with its
))
)
56
regenerative abilities?
The feeding of Tritonia festiva on alcyonacean octocorals is a
vivid example of partial predation. I have observed octocoral colonies
being overgrown by Halisarca sp., colonial tunicates, and the social
tunicate Metandrocarpa taylori Huntsman, 1912. It would be interesting
to compare overgrowth of the octocoral in the presence or absence of
Tritonia festiva.
Partial predation grades into parasitism. The small, abundant
dorid Rostanga pulchra feeds on the upper layers of orange sponges (pers.
obs.) and appears to be more parasitic than predatory (though more data
are needed on its movements, feeding rates, and sponge growth rates).
By damaging the sponge, such superficial grazing may increase the
sponge's susceptibility to overgrowth or speed up overgrowth interactions
already begun. On the other hand, such feeding could possibly facilitate
release of allelopathic chemicals and prevent or slow overgrowth.
One vivid example I have of the possible relationship between nudi-
2branchs and the encrusting community is a photograph of about 60cm of
boulder undersurface. The area is completely covered by the bryozoans
Eurystomella bilabiata and Hincksina velata and the sponge Zygherpe
hyaloderma. Two clumps of an unidentified arborescent bryozoan are
growing on the Hincksina. Eurystomella and Hincksina are overgrowing
each other in different parts of the area, and the sponge is overgrowing
Hincksina, but is being overgrown by Eurystomella. Each of these
organisms has at least one nudibranch predator at Cape Arago.
57
The competitive relationships between encrusting organisms can be
very complex. Overgrowth outcomes vary between the same two species
and often depend on encounter angle (Jackson, 1979). Overgrowth may
not be complete and certainly does not always result in mortality.
Moreover, growth, regeneration, and recruitment rates of the encrusting
species can all affect the observed diversity (Karlson and Jackson,
1981). If one adds predation (complete and partial) by organisms like
nudibranchs to this already complex system, as well as the other factors
affecting diversity previously mentioned, what one is left with is an
extraordinarily complex community for which competitive equilibrium
seems unlikely. Rather, there is probably a "dynamic equilibrium",
changing on both long and short time scales, between the rates of com-
petitive displacement and the rates at which the other factors act to
prevent competitive exclusion (Huston, 1979). Organisms do the best
they can to cope with these factors, and, to paraphrase some evolutionary
theory, the fit is by no means perfect - it only works.
Benthic Opisthobranchs Known from Oregon
The 66 benthic opisthobranch species presently known from Oregon
are listed in Table 4. Forty-seven of these have been found at Cape
Arago. Twenty-six are new records for Oregon, and 28 are new to Cape
Arago. The ranges of Adalaria sp. and Anisodoris lentiginosa are ex-
tended southward, and those of Crimora coneja, Cuthona cocoachroma,
C. flavovulta, C. fulgens, Diaphana californica, and Polycera atra
-"
Table 4. Benthic opisthobranchs known from Oregon
,,>,.;>~
Species
Acanthodoris hudsoni MacFarland, 1905
Acanthodoris nanaimoensis O'Donoghue, 1921
Adalaria sp.
Aeolidia papillosa (Linnaeus, 1761)
Alderia modesta (Loven, 1844)
Aldisa sanquinea (Cooper, 1863)
Aldisa cooperi Robilliard and Baba, 1972
Ancula pacifica MacFarland, 1905
Anisodoris lentiginosa Millen, 1982
Anisodoris nobilis (MacFarland, 1905)
Aplysiopsis smithi (Marcus, 1961)
Archidoris montereyensis (Cooper, 1863)
Archidoris odhneri (MacFarland, 1966)
Armina californica (Cooper, 1863)
Reference~(
2
2,5,6,8
8
1,4,5,8
4,5,8
1,8
8
8
8
1.4,5,8
4,5,8
1,2,5,8
4,8
3,5
Occurs at
Cape Arago
x
x
x
x
x
x
x
x
x
x
x
VI
co
~,~,
Table 4 (cont.)
",,-,.
Occurs at
Species Reference)~ Cape Arago
Bathydoris sp. 4,5
Berthell~ californica (Dall, 1900) 8 x
CadI ina flavomaculata MacFarland, 1905 1
Cadlina luteomarginata MacFarland, 1966 1,4,5,8 x
Cadlina modesta MacFarland, 1966 8 x
Catriona columbiana (O'Donoghue, 1922) 2,8 x
Crimora coneja Marcus, 1961 8 x
Cumanotus beaumonti (Eliot, 1906) 8
Cuthona abronia (MacFarland, 1966) 2,8 x
Cuthona albocrusta (MacFarland, 1966) 2,8 x
Cuthona cocoachroma Williams and Gosliner, 1979 8 x
Cuthona flavovulta (MacFarland, 1966) 8 x
Cuthona fulgens (MacFarland, 1966) 8 x
V1
\.0
".'''~..t
Table 4 (cont.)
Species
Dendronotus frondosus (Ascanius, 1774)
Dendronotus subramosus MacFarland, 1966
Diaphana californica Dall, 1919
Diaulula sandiegensis (Cooper, 1863)
Dirona albolineata Cockerell and Eliot, 1905
Dirona picta MacFarland in Cockerell and Eliot, 1905
Discodoris heathi MacFarland, 1905
Doto amyra Marcus, 1961
Doto columbiana O'Donoghue, 1921
Doto kya Marcus, 1961
Elysia hedgpethi (Marcus, 1961)
Eubranchus olivaceus (0 'Donoghue, 1922)
Eubranchus rustyus (Marcus, 1961)
Fiona pinnata (Eschscholtz, 1831)
Reference*
1,2,5,8
8
8
1,2,5,8
1,2,5,8
4,5
1,4,5,8
8
4,5
8
8
8
8
5,8
Occurs at
Cape Arago
x
x
x
x
x
x
x
x
x
x
x
'"o
Table 4 (cont.)
Species
Flabellina fusca O'Donoghue, 1921
Flabellina trilineata (O'Donoghue, 1921)
lIallaxa chani Gosliner and Williams, 1975
Hermaea vancouverensis O'Donoghue, 1924
Hermissenda crassicornis (Eschscholtz, 1831)
Hopkinsia rosacea MacFarland, 1905
Janolus fuscus O'Donoghue, 1924
Laila cockerelli MacFarland, 1905
Melanochlamys (Aglaja) diomedea (Bergh, 1894)
Melibe leonina (Gould, 1852)
Onchidoris bilamellata (Linnaeus, 1767)
Onchidoris muricata (Muller, 1776)
Onchidoris sp. (Q. hystricina)
Reference)~
2
2,5,8
8
1,8
1,2,5,8
7
1,2,4,5,8
1,2,5,8
3,5
3
1,4,5,8
8
8
Occurs at
Cape Arago
x
x
x
x
x
x
x
x C1'
I-'
Table 4 (cont.)
Species
Phyllaplysia taylori Dall, 1900
Placida dendritica (Alder and Hancock, 1843)
'Polycera atra MacFarland, 1905
Polycera zosterae O'Donoghue, 1924
Precuthona divae Marcus, 1961
Rostanga pulchra MacFarland, 1905
Tochuina tetraquetra (Pallas, 1788)
Triopha catalinae (Cooper, 1863)
Triopha maculata MacFarland, 1905
Tritonia diomedea Bergh, 1894
Tritonia festiva (Stearns, 1873)
Tritonia sp.
Reference*
3,5
8
8
8
8
1,2,5,8
4,5
1,2,5,8
8
3,5
1,2.5.8
4,5
Occurs at
Cape Arago
x
x
x
x
x
x
x
x
CJ\
N
Table 4 (cont.)
Occurs at
Questionable Species Reference* Cape Arago
Cadlina pacifica Bergh, 1879 1 x
Cuthona (Trinchesia) sp. 4
Eubranchus sp. 2
Pleurobranchus sp. 2
Pleurobranchus sp. 4,5 x
* 1 Sowell (1949)
2 Sphon (1972)
3 references cited by Sphon (1972)
4 Belcik (1975)
5 Belcik (1965)
6 Steinberg (1963a)
7 Steinberg (1963b)
8 present study
0\
W
64
northward. Depending on the status of the questionable species listed
in Table 4 (see below), the Oregon total could rise to 71 and the Cape
Arago total to 49.
Both Sphon (1972) and Belcik (1975) reported finding a
Pleurobranchus sp., Sphon from Strawberry Hill, and Belcik from Cape
Arago. These specimens could be different from each other and Berthella
californica, or one (or both) could be B. californica.
The Trinchesia sp. (which I have listed as Cuthona sp.) reported by
Belcik (1975) on Tubularia sp. in the Charleston boat basin could well
be Catriona columbiana. In my experience in the area, only Catriona
columbiana, Flabellina trilineata, and Hermissenda crassicornis occur on
Tubularia marina (and Cumanotus beaumonti on Tubularia crocea).
Until the Eubranchus sp. collected by Sphon (1972) can be re-examined,
it is impossible to ascertain whether it is an already described Eubranchus
species (including one of the two in Table 4) or belongs to an undescribed
species.
Sowell's (1949) report of Cadlina pacifica from Cape Arago is ques-
tionable. To my knowledge no other specimens of this dorid have been
found since Bergh's (1879) description of three specimens collected by
Dall in Alaska. Sowell reported finding at least five specimens and
does not describe any aspect of them except (p. 22) that they were "..•
always white about the same as the ground color of Cadlina marginata."
My guess is that these were specimens of Archidoris odneri, a white dorid
that was undescribed at the time.
65
Belcik (1965) found T. festiva and!. diomedea (=!. exsulans),
the two species of Tritonia presently known from the Pacific Northwest.
It thus seems likely that the "whitish" Tritonia sp. he reported dredged
off Cape Arago (Belcik, 1965, 1975) is an undescribed species, possibly
that pictured by Behrens, 1980, p. 103. For this reason I have not
listed Tritonia sp. under the "questionable species" in Table 4.
Belcik's (1965) Master's thesis on the parasitic copepod Ismaila
monstrosa Bergh contains an appendix listing 32 species of Oregon
opisthobranchs that he had examined for parasites. 15 of these species
were not found by Sphon (1972) and became the basis of Belcik's 1975
paper. However, Belcik (1975) includes an additional two species
(Trinchesia sp., which I have listed as Cuthona sp., and Archidoris
odhneri) that were not mentioned in his Master's thesis. And the appen-
dix to his thesis contains one species (Fiona pinnata) which Sphon did
not find but which Belcik, for some reason, did not include in his 1975
paper. An "Eolis sp." is also mentioned in the thesis and not in the
1975 paper. Presumably this is the same as the Trinchesia sp. mentioned
above, and thus I have not included it in Table 4. I have included
Belcik (1965) as a reference in Table 4 in order to present the 17 ad-
ditional species he found, but did not include in his 1975 paper. Both
Behrens (1980) and McDonald and Nybakken (1980) list Dillon Beach,
Marin County, California as the northern limit of Dirona picta. However,
Belcik (1975) found it on the docks of the Charleston boat basin. I saw
one specimen of Q. picta collected by the summer 1983 O.I.M.B. Inverte-
brate Zoology class. The collection location is unknown.
66
Sowell reported finding a form of Hermissenda crassicornis at North
Cove " ... among Laminaria and Costaria and in association with Triopha
carpenteri and Dirona albolineata." He further states, "This form ap-
pears to be specifically distinct from~. crassicornis, but has not been
definitely determined." This form is undoubtedly Janolus fuscus which
occurs in large numbers in the same habitat as Triopha catalinae and
Dirona albolineata. Belcik (1975) wrote that Sowell " .•• confused this
form with Coryphella sp. or Antiopella spp."
Steinberg (1963b) recorded Coos Bay, Oregon as the northern limit
of Hopkinsia rosacea. This is the only record of H. rosacea north of
Gualala, Mendocino County, California (Marcus, 1961, p. 29). Specimens
of H. rosacea from Coos Bay were apparently collected by Lawrence
Andrews, whom Steinberg (1963a) cited as her source of opisthobranch
specimens from Coos Bay. The only other species Steinberg (1963a or b)
reported from Coos Bay was Acanthodoris nanaimoensis.
Belcik (1975) reported Alderia modesta as uncommon on Vaucheria
mats on mudflats in Coos Bay. At least during the summer, A. modesta
can be found in abundance feeding on mats of Vaucheria sp. in the South
Slough of Coos Bay (pers. obs.).
Five additional species that I have observed in the Coos Bay area,
but not at Cape Arago, are Cumanotus beaumonti, Elysia hedgpethi, Fiona
pinnata. Onchidoris bilamellata, and Polycera zosterae. C. beaumonti
occurs on Tubularia crocea (Agassiz, 1862) in the Charleston boat basin;
a single specimen of ~. hedgpethi was collected in Coos Bay by the summer
1983 O.I.M.B. invertebrate zoology class; K. pinnata occurs offshore on
67
floating objects covered with its prey, the gooseneck barnacle Lepas sp.;
Q. bilamellata is found among Balanus glandula Darwin, 1854 on the pil-
ings and breakwater of the Charleston boat basin; and a single P.
zosterae was collected from a piling in the Charleston boat basin.
68
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Typed By: Marge Lebow