MINOR PHYLA 



355 



large mouth that opens into a muscular pharynx lined with teeth. Pri- 

 apuloids plow through mud and swallow whole whatever prey they can 

 seize. The nervous system resembles that of the echiuroids and a cir- 

 culatory system is lacking. Young priapuloids have a sheath of cuticular 

 plates enclosing the posterior, nonretractile portion of the body. Their 

 early development is unknown. 



For many years these animals have been allied with the sipunculoids 

 and echiuroids. Recently, however, notice was taken of the fact that 

 although the body cavity is lined with a membrane it is not cellular, 

 and the possibility arises that the cavity is a pseudocoelom. Comparisons 

 have been made between the young and some of the rotifers (although 

 they differ greatly in size). The poorly developed nervous system and ab- 

 sence of a circulatory system are further evidence for grouping the 

 priapuloids with the Aschelminthes. The digestive tract, however, is 

 completely muscularized, and the large size and general appearance of 

 these worms do not suggest a pseudocoelomate affinity. Until their early 

 development is learned the true relations of this group probably will not 

 be known, and for the present they will be left as a group related to the 

 annelids. 



161. The Phoronlds and Brachiopods 



The Phoronida and Brachiopoda (Fig. 18.3) include medium-sized 

 sessile marine animals with a lophophore, a circle of ciliated tentacles sur- 

 rounding the mouth. Typically the lophophore in these phyla is drawn 



Pho 



i''onii 



Bra-chiopoda- 

 -Tcntacles icuit) C 



'Terrt a.clcB 

 "Lophopliore 



Figure 1 8.3. Phoronida: A, Whole animal in side view. B, Half of anterior end show- 

 ing internal organs. (After Parker and Haswell.) Brachiopoda: C, Side view of shell. 

 D, Side view showing internal structure. (After Borradaile, et al.) 



