THE PHYLUM CHORDATA 



67 



limeter in length. Each individual inhabits a delicate flexible tube 

 into which the body may be withdrawn.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

 sembles Ccphalodiscus, but differs 

 chiefly in the lack of some of the or- 

 gans possessed by the latter. There 



Fig. 39. — Rhabdopleura. 

 a, mouth; h, 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. 



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 typo) . The really strik- 

 ing point of contact is between the 

 larva of Phoronis and Balanoglossus. 

 as a somewhat simplified Balanoglos 

 the collar fringed with tentacles, and 



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; st, stalk 

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

 cirawn from Parker and Haswell, 

 after Schepotieff.) 



This larva may be described 



■.SM.S, since it has the proboscis, 



the short trunk terminating m 



