CHAPTER XVI 



CLASSES SCAPHOPODA AND PELECYPODA 



CLASS SCAPHOPODA 



Head rudimentary, mantle edges ventrally con crescent, 

 forming a tube 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, the concave side being the dorsal ; 

 muscles near the posterior end attach the 

 body 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 (^JDentalium)^ some- 

 times a terminal retractile disc (^Siplionoden- 

 taliurri)^ sometimes a retractile disc with a 

 central tentacle (^Pulselluni) . 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, 



J IG. ZJJ. An3,t011iy 01 . . - 11/' r>o/^N • ^ 



Uentalium: a, interior COUtaUimg the radula (p. 'ASb), IS at the 



aperture of mantle;/, ^^sc 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. 

 There are no eyes, but on each side of the mouth are small 

 bunches of exsertile filaments (jcaptaculd)^ which appear to act as 



foot; g, genital gland; 

 k, kidney; I, liver. 

 (After Lacaze - Du- 

 thiers.) 



