276 PRIAPULIDA 



ing a single circle around the mouth; alimentary canal not spiral or 



incompletely so; no spindle muscle; 2 retractors; but 1 brown tube: 15 



to 20 species. 



P. strombi (Montagu) (Fig. 447). Body 30 mm. long, with papillae; 



a band of minute hooks back of tentacles, and large, dark-brown, cres- 

 centic or triangular hooks pointing forwards on the 

 hinder part: common in 2 to 1,000 fathoms from the 

 "West Indies to the Arctic Ocean; Mediterranean; the 

 worm lives in a snail shell, closing the aperture by means 

 of sand cemented into a firm mass, leaving a hole through 

 which the introvert is thrust out, and moves about car- 

 rying the shell with it; common, there being many 



Fig. 447 



Phascoiion varieties, some of which form a thick short tube of mud 



strombi 



(Gerouid). and sand. 



Class 2. PRIAPULIDA. 



Body without tentacles; anus at the hinder end; introvert plump 

 and covered with rows of small spines; trunk striated transversely and 

 in most species bearing 1 or 2 large caudal appendages with respiratory 

 papillae; alimentary canal in most cases straight and wide; pharynx 

 muscular, provided with numerous teeth; main nervous system sub- 

 epithelial, consisting of a ring around the mouth and a ventral cord 

 without definite ganglia; no special sense organs, blood- vascular system, 

 or nephridia in the adult, but in the young worm nephridia are present 

 which open into the genital ducts; sexes distinct; gonads paired; genital 

 ducts open to the outside near the anus: 2 genera and 6 species, which 

 are found in shallow water in the colder seas, where they burrow in the 

 sand and mud. 



PRIAPULUS Lamarck. Caudal appendages, covered with hollow- 

 papillae present; introvert thicker than the trunk, about a quarter as 

 long as it and with spines in longitudinal rows : 5 species. 



P. caudatus Lam. Length 2 to 18 cm., color yellow or brown: 

 Arctic seas. 



