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Description 
Size—one of the smaller phoronids: 15-30 
mm long (Silen 1954): sp. pallida. Sand 
covered tube just a little larger (Silen 1952); 
expanded animal can be 25% longer than 
tube. 
Color—trunk pale, white, posterior end light 
red. Internal organs visible as red (contain 
hemoglobin (Zimmer and Haderlie 1980). 
Tentacles white, without pigmented 
amoebocytes: sp. pallida (Silen 1954). Larva 
opaque yellow, tube yellow to brown-red 
(from secreted matter) (Silen 1954). 
Trunk—wormlike: un-segmented, smooth and 
soft, but faintly annulated (Hyman 1959), no 
setae - all characteristic of phylum Phoronida. 
Can be faintly differentiated into several 
zones: sp. pallida (Silen 1954). Trunk and 
whole tube curved toward anal side (Silen 
1954) (fig. 6). 
Lophophore—a horseshoe-shaped 
extension of the mesosome (Hyman 1959); 
includes mouth and consists of a crown of 
tentacles. Number of lophophore spirals, 
number of tentacles characteristic of sp.  
pallida - a single row of 50-140 tentacles, in a 
simple spiral (Emig 1974)(fig. 3). 
Tentacles—straight, finger-shaped: 
Phoronida (Zimmer and Haderlie 1980); not 
threadlike (fig. 2a). In P. pallida there can be 
50-140, but usually around 50 (Zimmer and 
Haderlie 1980), sometimes more (S.F. Bay 
specimens). Tentacles can be regenerated 
(MacGinitie and MacGinitie 1949). 
Anus—dorsal to mouth (Hyman 1959); 
digestive tract U-shaped (fig. 2). 
Nephridiopores—lateral to anus (fig. 2): 
excretory and for emission of sex cells 
(Hyman 1959). 
Collar—not present at base of lophophore: 
genus Phoronis (Zimmer 2007) (figs. 1, 2, 3). 
Lophophore base and trunk demarcation a 
slight groove; collar, (if present, as in genus 
Phoronopsis), extends all around trunk. (Do 
not confuse anus and nephridiopores on 
dorsal base of lophophore with a true collar.) 
 
 
 
Bulb—(ampulla)-enlarged posterior end (fig. 
1). 
Internal Structure—much systematic work 
based on longitudinal muscle patterns, etc., 
not easily studied by casual field worker. P. 
pallida muscles have unusual longitudinal and 
circular patterns, and few bundles of muscles 
(18-19). Giant nerve fibers found in this 
phylum - except in P. ovalis - also vary in 
size and number. P. pallida has one giant 
nerve fiber, on the left side - usual position in 
phylum (Emig 1974). Nephridial structure is 
also important in systematics. 
Tube—separate, vertical, chitinous, covered 
with thin layer of sand grains. Membranous 
distally (Zimmer 2007). Distinctly flexed 1/3 of 
way to base: sp. pallida (Silen 1954) (fig. 6). 
Tube flexible, tough, can't be easily broken. 
Basal end of tube open. 
Larva—actinotroch (from which this species 
was first described (Schneider 1862)) is small: 
0.6 mm long, active; found on water's surface. 
Mature larva found on substrate, has 5 pairs 
of tentacles (Silen 1954) (fig. 5). Young 
actinotrochs are photopositive and 
planktotrophic (Silen 1954). 
 
Possible Misidentifications 
Phoronids are worm-like, with an 
unsegmented, though slightly annulated trunk 
and a crown of tentacles on the anterior end. 
Some polychaetes also have this general 
form. Phoronids, however, have no setae or 
segmentation on their trunks. Phoronid 
tentacles are straight and finger-like, not 
branched or thread-like, as in polychaetes. 
The phoronid lophophore is circular-crescent 
shaped or a double spiral. 
Only 2 genera of Phoronida and probably 
fewer than 20 species are known worldwide. 
Many of these can be found on the Pacific 
coast, but only 3 are common intertidally: 
Phoronopsis harmeri, Phoronis 
vancouverensis, and P. pallida. The main 
population of each of these species is likely 
subtidal (Zimmer 2007). 
Phoronopsis spp. can be distinguished 
from Phoronis spp. by the presence in the 
Phoronis pallida 
A lophophorate coelomate (Schneider, 1862; Silen, 1952) 
Phylum:  Phoronida 
    Family:  Phoronidae 
   
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former of a collar at the base of the 
lophophore, lacking in Phoronis spp. The 
three Pacific representatives of this genus 
include: 
Phoronopsis harmeri Pixell, 1912 (senior 
synonym of P. viridis (Hilton, 1930), a large 
common phoronid often found in great 
masses on the mudflats. Individuals can 
be green or white and up to 200 mm long, 
with up to 300 green tentacles with white 
spots (Hyman 1959, Zimmer 2007). P. 
harmeri is usually larger than P. pallida (up to 
60 mm long), and has a collar, as in all 
Phoronopsis spp. It is also found in the 
Atlantic (Azores). This species is abundant on 
Oregon and Washington tidal flats, and is 
largely distinguished from P. pallida by its 
size, color and its collar. 
P. pacifica (Torrey, 1901), found first in 
Humboldt Bay, and described from Puget 
Sound as well, is also considered a synonym 
of P. harmeri (Emig 1974). 
The third Phoronopsis species, P. 
californica Hilton, 1930, is probably limited to 
southern California. It has a large bright 
orange lophophore with elaborate spirals; it is 
solitary, and can be up to 12" (300 mm) long 
(MacGinitie and MacGinitie 1949). 
There are four other species of Phoronis 
reported from our coast: 
P. architecta Andrews, 1890 is an Atlantic 
species, also found subtidally from southern 
California to British Columbia, and 
occasionally intertidally (Zimmer and Haderlie 
1980). Its lophophore is flesh-colored, or 
rarely reddish, with white bands and flecks. It 
has no collar, (like P. pallida), but is 2x the 
size of the latter; its sand encrusted tube is 
straight, not flexed.  
P. psammophila has been synonymized 
with P. architecta (Emig 1982).P. ovalis 
Wright, 1856 is much smaller even than P. 
pallida, (only 6 mm long). It bores in shell and 
limestone and is not found 
living freely in the mud. 
P. vancouverensis Pixell, 1912 (now 
senior synonym of P. ijimai Oka, 1897) is 
whitish, like P. pallida. It is larger, however, 
20-50 mm long, and has 72-100 tentacles 
(average 90 according to Pixell ,1912), and 
grows in intertwined clusters of great density, 
often on pilings and on rocks. Its tubes are 
covered with detritus, not sand grains.  
P. hippocrepia (Wright), the European 
species, is considered to be separate from P.  
vancouverensis above (Emig 1971). 
 
Ecological Information 
Range—Scandinavia; Pacific coast of North 
America. 
Local Distribution—Coos Bay: Charleston 
mudflats. 
Habitat—in soft sand, muddy sand (Emig 
1974); on intertidal mudflats. Commensal in  
Upogebia pugettensis burrows (Zimmer 2007) 
Salinity—all phoronids are marine (Zimmer  
and Haderlie 1980). Only one species, P. 
euxinicola, is found in brackish water, in the 
Black Sea (Hyman 1959). These specimens 
collected at 30 ‰ (Coos Bay). 
Temperature—phoronids are found in 
shallow waters of tropical and temperate 
ranges (Hyman 1959); most are temperate 
(Zimmer 1980). Some can regenerate after 
extremes of weather have left only fragments 
in tubes: in winter (Italy) and summer (Japan) 
(Hyman 1959). 
Tidal Level—intertidal, also subtidal at a 
number of locations worldwide (Zimmer 2007) 
down to 12m deep (Emig 1974). (Other 
phoronids can be found down to 140m.) 
Associates—commensal in burrows of 
Upogebia pugettensis, though not often found 
with the sympatric mud shrimp Neotrypaea 
californiensis (Zimmer 2007). 
 
Quantitative Information 
Weight— 
Abundance— 
 
Life History Information 
Reproduction—a simultaneous 
hermaphrodite: eggs and sperm extruded into 
body cavity from reproductive organs, fertile 
eggs expelled into seawater via 
nephridiopores (MacGinitie and MacGinitie 
1949). In some species, larvae live among 
tentacles of adult female, but not in P. pallida, 
which lacks nidamental (nesting) organs 
(Emig 1974). No asexual propagation, 
although regeneration of crown of tentacles 
possible (Silen 1952). Eggs laid on 2 - 3 
successive summer nights (Sweden), 28 at a 
time (Silen 1954). 
Growth Rate—fertilized egg immobile for 20 
hours; to blastula stage in 20 hours more. 
After gastrulation begins, hood develops; in 
25-30 more hours, a ciliated ridge appears, 
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becoming the crown of tentacles. First 
tentacles show after two days. (Growth 
stopped in lab after six days (Silen 1954). The 
actinotroch progresses from four tentacles to 
metamorphosis in 12-14 days. It is active and 
moves quickly horizontally and vertically - 
dives, floats, and rushes. Details of larval 
development and phylogenetic implications 
are given by Santagata (2004a) and a key to 
larval stages is available in Shanks (2001). 
Mature larvae are photonegative; pre-
settlement behavior is induced by a 
waterborne cue from Upogebia pugettensis, a 
shrimp species with which P. pallida is 
commensal (Santagata 2004b).  
Metamorphosis is triggered by 
presence of proper substrate (mud, sand), 
and takes 15 minutes. The actinotroch takes 
a horizontal position, ventral side down, then 
evaginates metasomal sac. The transition is 
made from control by the larval 
neuromuscular system to that of the juvenile, 
resulting in the apoptosis of larval structures. 
This succession of events suggests 
lophotrochozoan affinities (Santagata 2002). 
Finally, a thin tube is formed, and the worm 
begins to burrow.  
Longevity— 
Food—all phoronids are ciliary mucus 
feeders, gathering suspended particles by 
tentacular currents (Hyman 1959). 
Actinotrochs eat peridinians, not diatoms 
(Silen 1952). 
Predators— 
Behavior—movement limited to emergence 
from anterior end of tube, and expansion of 
crown (in undisturbed conditions), and to 
withdrawal into tube if disturbed (Hyman 
1959). Adults not light sensitive (Hyman 
1959). 
 
Literature Cited 
1. EMIG, C. C. 1971. Remarques sur la 
systmatique des Phoronidea. Marine 
Biology. 8:154-159. 
2. ——. 1974. The systematics and 
evolution of the phylum Phoronida. 
Journal of Zoological Systematics and 
Evolutionary Research. 12:128-151. 
3. EMIG, C.C. 1982. The biology of 
Phoronida. Advances in Marine 
Biology. 19: 1-89. 
4. HYMAN, L. H. 1959. Invertebrates: 
Smaller coelomate groups. McGraw-
Hill, New York. 
5. MACGINITIE, G. E., and N. 
MACGINITIE. 1949. Natural history of 
marine animals. McGraw-Hill Book 
Co., New York. 
6. PIXELL, H. L. M. 1912. Two new 
species of the Phoronidea from 
Vancouver Island. Quarterly Journal of 
Microscopical Science. 58:257-284. 
7. SANTAGATA, S. 2002. Structure and 
metamorphic remodeling of the larval 
nervous system and musculature of 
Phoronis pallida (Phoronida). 
Evolution & Development. 4(1): 28-42. 
8. --------------- 2004a. Larval 
development of Phoronis pallida 
(Phoronida): Implications for 
morphological convergence and 
divergence among larval body plans. 
Journal of Morphology. 259: 347-358. 
9. ----------- 2004b. A waterborne cue for 
the actinotroch larva of Phoronis 
pallida (Phoronida) produced by 
Upogebia pugettensis (Decapoda: 
Thalassinidea). Biological Bulletin. 
207(2): 103-115. 
10. SCHNEIDER, A. 1862. Uber die 
Metamorphose der Actinotrocha 
branchiata. Archiv fur Anatomie und 
Physiologie:47-65. 
11. SHANKS, A.L. 2001.  An identification 
guide to the larval marine 
invertebrates of the Pacific northwest.  
Oregon State University Press, 
Corvallis, OR. 
12. SILEN, L. 1952. Researches on 
Phoronidea of the Gullmar Fiord Area 
(West coast of Sweden). Arkiv för 
Zoologi. 4:95-140. 
13. ——. 1954. Developmental biology of 
Phoronidea of the Gullmar Fiord area 
(West coast of Sweden). Acta 
Zoologica. 35:215-257. 
14. ZIMMER, R. L. 2007. Phylum 
Phoronida, p. 860-863. In: Light's 
manual; intertidal invertebrates of the 
central California coast. J. T. Carlton 
(ed.). U.C.Press, Berkeley. 
15. ZIMMER, R. L., and E. C. HADERLIE. 
1980. Chapter 7: Brachiopoda and 
Phoronida, p. 108-116. In: Intertidal 
invertebrates of California. R. H. 
Morris, D. P. Abbott, and E. C. 
Haderlie (eds.). Stanford University 
Press, Stanford, California. 
 
Digitized 2012 – Last Updated 2014 by Kirstin Meyer– E-mail corrections to oimbref@uoregon.edu