CHAPTER XVI 



CLASSES SCAPHOPODA AND PELECYPODA 



CLASS SCAPHOPODA 



Head rudimentary, mantle edges veutrally concrescent, forming 

 a tulje opening before and behind, and 

 covered with a shell of the same shape ; sexes 

 separate. 



The Scaphopoda form a small but very 

 distinct class, whose organisation is decidedly 

 of a low type. The body is usually slightly 

 curved, tlie concave side being the dorsal ; 

 muscles near the posterior end attach the 

 l)ody to the shell. The foot, which can be 

 protruded from the anterior or wider aper- 

 ture, is rather long, pointed, and has some- 

 times two lateral lobes {Dentalitivi), some- 

 times a terminal retractile disc (^Sij)honodcn- 

 talnctn), sometimes a retractile disc with a 

 central tentacle {PnhcUum). The cephalic 

 region, as in Pelecypoda, is covered by the 

 mantle. The mouth is situated on a kind of 

 projection of the pharynx ; the buccal mass, 

 containing the radula (p. 236), is at the 

 base of the foot, and the intestine branches 

 forward from the front part of the stomach. 

 The liver (Fig. 299) is paired, and consists 

 of a number of symmetrical^ radiating coeca. 

 but on each side of the mouth are small 

 filaments {cajptacidct), which appear to act as 



Fig. 299. — Anatomy of 

 JJenfalmm : a, anterior 

 aperture of mantle ; /, 

 foot ; ff, genital gland ; 

 k, kidney ; I, liver. 

 (After Lacaze - Du- 

 thiers.) 



There are no eyes, 

 bunches of exsertile 



