THE PHYLUM CHORDATA 



67 



iimeter in length. Each individual inhabits a delicate flexible tube 

 into which the body may be withdrawn. Rhabdopleura in general re- 

 sembles Cephalodiscus, but differs 

 chiefly in the lack of some of the or- 

 gans possessed by the latter. There 



FIG. 39. Rhabdopleura. 

 a, mouth; 6, anus; c, stalk; 

 d, proboscis; e, intestine; /, an- 

 terior region of trunk; g, a ten- 

 tacle. (From Hegner, after 

 Lankester.) 



are no gill-slits nor proboscis pores. 

 The dorsal region of the collar 

 bears but a single large pair of 

 feathery tentacles which form the 

 most conspicuous part of the 

 animal. 



st 



ORDER III. PHORONIDEA 



Phoronis is a small tubicolous 

 animal with a general resemblance 

 to Rhabdopleura. It has been 

 classified as a gephyrean (an aber- 

 rant annelid type) . The really strik- 

 ing point of contact is between the 

 larva of Phoronis and Balanoglossus. This larva may be described 

 as a somewhat simplified Balanoglossus, since it has the proboscis, 

 the collar fringed with tentacles, and the short trunk terminating in 



FIG. 40. Internal view of Rhabdo- 

 pleura. a, anus; dn, dorsal nerve* 

 i, intestine; m, mouth; nc, notochord; 

 p, proboscis; pc, proboscis cavity; 

 ph, pharynx; s, stomach; si, stalk; 

 t, tentacles; tc, trunk cavity. (Re- 

 drawn from Parker and Haswell, 

 after Schepotieff.) 



