248 PHYLUM ANNELIDA. 
Appendix (4) to Annelid Series 
Under the old term Molluscoidea are sometimes included the three 
classes—Phoronoidea, Polyzoa or Bryozoa, and Brachiopoda. 
The Molluscoidea are characterised by the presence of a true 
ceelom, formed in development by the folding off of pouches from 
the archenteron, and by the shortening of the dorsal region of the 
body, which results in the close approximation of mouth and anus. 
The mouth is typically furnished with ciliated tentacles, and is often 
overhung by an epistome; both tentacles and epistome, when present, 
contain spaces which are part of the body cavity. Except in the 
Ectoprocta among Polyzoa, two or four nephridia are present, and 
serve also as genital ducts. There is always a metamorphosis in 
development, and the larvee are peculiar. 
The development is in most cases in- 
sufficiently known, and it is probable 
that further knowledge of it will remove 
these sets of animals from their apparently 
anomalous position. 
Class PHORONOIDEA. 
This class was erected for the genus 
Phoronis, which has been associated both 
with the Gephyrea and with Polyzoa. 
Another genus, Phoronopsis, from the 
Cape, has been recently established. It 
has been proposed to associate these 
two genera, along with Cephalodiscus 
and Rhdbdopleura, with the Hemi- 
chorda, on account of certain Chordate 
affinities, said to be exhibited by the 
larva, 
The genus Phoronis includes a few 
species of small marine ‘‘ worms,” social 
in habit, and found enclosed in fixed 
leathery tubes often encrusted with foreign 
particles. Each individual is furnished 
with a horseshoe-shaped crown of tent- 
Fic. 127.—Actinotrocha or 
larva of Phoronis.—After 
Masterman. 
The mouth is overhung by the 
prominent pre-oral hood; the 
anus is at the other endof the 
body. Behind the mouth is a 
ring of ciliated tentacles. 
SP., the nerve ganglion in the 
hood; V.G., the nerve gan- 
glion of the region called collar 
region by Masterman; ClV&., 
nerve-ring- at base of tentacles. 
acles, which are hollow and supported 
by an internal skeleton. The nervous 
system lies in the ectoderm—a very 
primitive character, and consists of a 
ring round the mouth, and of a cord 
down the left side of the body. An 
interesting point is the presence of a 
closed vascular system with nucleated 
