240 



THE BIOLOGY OF MARINE ANIMALS 



(Fig. 5.27). Perforating the septum are small pores provided with valves 

 and sphincters. Normally the septum lies quiescent with open pores, 

 through which a slight current is maintained by lateral cilia. Several times 

 each minute, however, the septum is lowered slowly, pores are closed, then 

 the septum is quickly lifted, causing water to be expelled through the 

 exhalant siphon and water and food to be sucked in through the inhalant 

 siphon. The food is retained in the infra-septal cavity by a large valve 



Foot 



Byssus groove 



Valve 



Anterior 

 palps 



Tentacles 



Mouth 



Poster/ 

 palps 



Mantle 

 edge 

 Anterior and 

 posterior branchial sieves 



l. J 



Fig. 5.27. Septibranch Bivalves 



(a) Ventral view of Poromya granulata with mantle lobes drawn back to expose the 

 septum. Large arrows indicate direction of food ; small arrows, water currents through 

 the branchial sieves, (b) Movements of septum in Cuspidaria, (i) position of septum at 

 rest and prior to descending ; current of water through pores indicated by upward arrows ; 

 downward arrows indicate initial septal movement; (ii) position of septum at end of 

 downward movement, pores closed; septum now moves upwards as indicated by arrows; 

 (iii) position at completion of upward movement, pores still closed. (From Yonge, 1928.) 



guarding the opening from the inhalant siphon and is pushed into the 

 mouth by small muscular palps. Cilia are greatly reduced and are con- 

 cerned with the removal of fine particles from the mantle cavity (111). 



Cephalopods capture prey by means of arms and tentacles bearing 

 sucking discs. Cuttlefish and octopus feed on fish and decapod Crustacea. 

 The prey is conveyed to the mouth by the appendages, torn by the horny 

 jaws and rasped by a radula. Several salivary glands discharge into the 

 mouth region, namely the sublingual, anterior and posterior salivary 

 glands. The latter two are generally regarded as poison glands. The secre- 



