V. PHORONIDEA. VI. BRACHIOPODA. 325 



Class V. Phoronidea. 



The single genus Phoronis* occurs on our eastern shores. 

 The animal was first placed among the Chaetopoda on account of 

 its worm-like body situated in a chitinous tube like many sedentary 

 annelids. Then it was placed in the Polyzoa, with which it is 

 more nearly related. The young, described as Actinotrocha, is a 

 modified trochophore with the mouth overhung by a large hood 

 and the postoral band of cilia drawn out into a series of fingers 

 which become the tentacles of the adult; the anus is terminal. 

 At the time of metamorphosis this larva becomes doubled on itself 

 by a complicated process, so that the alimentary canal is U-shaped 

 and the anus is near the mouth, while the tentacles are borne on a 

 horseshoe-shaped basis around the mouth. 



Class VI. Brachiopoda. 



On account of the bivalve calcareous shells the Brachiopoda 

 were long regarded as molluscs, but later the fact that the valves 

 are not paired as in the lamellibranchs, but are dorsal and ventral, 

 that the nervous system, the excretory and reproductive organs, 

 the body cavity, and the development resemble those of the annelids 

 rather than those of the molluscs, led to their recognition as a dis- 

 tinct class allied to the former group. 



The body has a greatly shortened long axis (fig. 298) and in 

 consequence a transversely oval visceral sac. In most a stalk (st) for 



FIG. 298. Anatomy of Rhynchonella psittacea. (After Hancock.) a', left, ', right 

 arm; a, opening into the cavity of the arm: d, intestine; e, blind end of the intes- 

 tine ; 0, stomach with liver; m, adductors and divaricators of shell; o, oesophagus; 

 p', p 2 , dorsal and ventral mantle lobes; sf, stalk; 1, 2, first and second septum, on 

 the second a nephrostome. 



attachment arises from the posterior end. From the anterior side 

 two folds, the mantle lobes, extend forwards (/?), one ventral, the 



