FLATWORMS AND THREADWORMS 



311 



There is a larval trochophore stage. They ordinarily live in crevices 

 of rocks. 



(2) The Sipunculoidea, which are unsegmented. They possess one 

 pair of nephridia, a large coelom and anal opening on the dorsal surface, 

 near the head-end. They usually possess tentacles at the anterior end. 

 They live in sand or bore their way into coral rock. 



(3) The Priapuloidea are also unsegmented, having an anterior- 

 mouth surrounded by chitinous teeth and the anal opening in the pos- 



Fig. 200. 



Magellania flavescens (of the group 

 Brachiopoda). A, dorsal aspect of shell. B, 

 shell as seen from the left side, b, beak ; d.v., 

 dorsal valve ; /, foramen ; v.v., ventral valve. 

 (From Weysse, after Davidson.) 



Anatomy of a Brachiopod, Waldheimia 

 austrdlis. 1, mouth ; 2, lophophore ; 3, stom- 

 ach ; 4, liver tubes ; 5, median ridge on shell ; 

 6, heart ; 7, intestine ; 8, muscle from dorsal 

 valve of shell to stalk ; 9, opening of nephrid- 

 ium ; 10, stalk ; 11, body-wall ; 12, tentacles ; 

 13, coil of lip ; 14, terminal tentacles. (From 

 Shipley and MacBride.) 



Fig. 201. 



A. Echiurus pattasii (of the group 

 Gephyrea). a, mouth at the end of the grooved 

 proboscis; b, ventral hooks; c, anus. (From 

 the Cambridge Natural History.) 



B. Sipunculus nudus (of the group 

 Gephyrea) laid open from the side. A, anus; 

 BD, brown tubes (nephridia); D, intestine; 

 G, brain ; Te, tentacles ; VG, ventral nerve- 

 cord. (From Sedgwick, after Keferstein.) 



C. Priapulus candatus (of the group 

 Gephyrea ) . a, mouth surrounded by spines. 

 (From the Cambridge Natural History.) 



terior region. They live in mud and sand. The head-end usually pro- 

 jects above the surface of the mud in which they lie. 



References : 



Ward and Whipple, "Fresh Water Biology." 

 Hegner's "College Zoology." 



Pfatt's "Manual of the Common Invertebrate Animals." 

 Braun & Liihe, "A Handbook of Practical Parasitology." 

 W. H. MacCallunn, "A Text-book of Pathology." 

 Damaso Rivas, "Human Parasitology." 



Kolle & Wassermann, "Hand-buch der Pathologenen Mikroorganis- 

 men." 



Hegner & Coit, "Diagnosis of Protozoa and Worms Parasitic in 

 Man." 



