VII 



MOLLUSCA SYSTEMATIC REVIEW 



21 



Xylophaga). Fam. Teredinidae : boring mussels ( Teredo [Fig. 29]). Fam. Clava- 

 gellidse (Clavagella, Brechites [Aspergillum, Fig. 30]). 



Sub-Order 7. Anatinacea. 



Mantle to a great extent closed. With siphons and foot. Hermaphrodite. 

 Fam. Pandoridse, Lyonsiidse, Anatinidae (Anatina, Thrada). 



ORDER 5. Septibranchia. 

 The ctenidium on each side is transformed into a muscular septum pierced by 



A 



d 



FIG. 31. Soft body of Silenia Sarsii (Cuspidaria), after Pelseneer. A, Left aspect after 

 removal of the mantle ; B, ventral aspect after removal of most of the mantle ; a, p, anterior and 

 posterior ; d, v, dorsal and ventral ; d, s, right and left ; 1, anterior adductor ; 2, mouth ; 3, anterior 

 group of branchial slits; 4, hepatic mass ; 5, branchial septum ; 6, posterior group of branchial slits ; 

 7, posterior adductor ; 8, anal siphon ; 9, siphonal tentacles ; 10, valve of the branchial or inhalent 

 aperture ; 11, point where the free mantle edges limiting the pedal aperture fuse ; 12, median group 

 of branchial slits ; 13, free edges of mantle ; 14, foot ; 15, posterior labial palps ; 16, anterior labial 

 palp. 



slits, which divides the mantle cavity into two chambers, one lying above the other. 

 Hermaphrodite. Fam. Poromyidae, Cuspidaridse (Fig. 31 A and B). 



CLASS V. Cephalopoda (Cuttlefish). 



Body symmetrical with high visceral dome. The mouth is surrounded by 

 tentacles or prehensile arms, which may be considered as portions of the foot 

 developed round the mouth. Another portion of the foot forms the siphon. In 



