CHJETOGNATHA 271 



P. architecta Andrews (Fig. 442). Tubes straight and about 13 cm. 



long and 1 nun. wide; anterior portion of body flesh color, posterior 

 portion reddish or yellowish; tentacles about 100 in number; lophophore 

 not spirally coiled at the ends: North Carolina, in sand flats near the 

 low-water mark, the tubes being isolated and covered with sand grains; 

 often connnon. 



P. pacifica Torrey. Length of tube 9 cm.; diameter 2 mm.; each 

 spiral of lophophore with 1^/^ to 2 turns; tentacles 170 to 200 in number; 

 tube straight, cylindrical, incrusted with sand: Puget Sound; Humboldt 

 Bay, California; in sand and mud flats. 



SuBPHYLUM 7. CH^TOGNATHA.* 



Elongate, transparent worms of small size which live exclusively in 

 the sea, preying on other small organisms. The body is long and slender 

 and imciliated, and is provided with two or three pairs of horizontal fins. 

 SuiTounding the mouth at the front end of the body are long, paired, 

 prehensile bristles or hooks and one or two rows of small teeth (Fig. 

 443, B). A large body cavity is present, which is lined with a peritoneum 

 and is divided by transverse septa into three compartments. The anus -is 

 at the hinder end of the body and between it and the mouth lies the 

 straight digestive tract: longitudinal mesenteries join the intestine with 

 the dorsal and ventral body walls. The nervous system is subepithelial; 

 a large cerebral ganglion forms the brain and is connected with a large 

 ventral trunk ganglion in the middle of the body by commissures. The 

 brain sends off nerves to the two eyes and the unpaired olfactory organ 

 behind them. No special respiratory, excretory, or circulatory organs are 

 present. The animals are hermaphroditic, the sex cells arising from the 

 peritoneum. The two ovaries are in the middle division of the body, the 

 oviducts opening near them: the testes are in the hinder division of the 

 body; the spermatozoa escape to the outside through a pair of prominent 

 seminal vesicles just in front of the tail fins. In the development the 

 mesoderm is formed by the growth of paired pouches from the archenteric 

 walls, the fused cavities of the pouches becoming the coelom, a process 

 characteristic of many annelids and also of the Cliordata. 



The Chcetognatha are found in all seas, from the surface to the 

 greatest depths, being often present in immense numbers. Six genera and 

 about 30 species are known. 



* See "The Known Chaetognatha of American Waters," by F. S. Conant, Johns 

 Hopk. Univ. Cir., Vol. 15, p. 82, 1896. "Chsetognathi," by R. von Ritter-Zahony, Das 

 Tierreich, 1911. "Classification, etc., of the Chsetognatha," etc., by E. A. Michael, 

 Univ. of Cal. Pub., Vol. 8, p. 21, 1911. 



