NUTRITION AND FEEDING MECHANISMS 



211 



confluent, and are directed to the exterior as a single dorsal exhalant 

 current. 



In another brachiopod, Neothyris, the mechanism is somewhat different. 

 Two lateral arms of the lophophore lead into a spiral confluent chamber, 

 enclosed by tentacles. On either side of the gape the tentacles are spread 

 apart so as to form inhalant openings (Fig. 5.9). Through the latter a 

 stream enters the inhalant chamber formed by the opposed tentacles of 

 the lophophore, and escapes into the exhalant chamber by passing 

 between the filaments of the spiral arm. Water currents are created by 

 beating of cilia lining the exhalant chamber and spiral arm. Heavy part- 

 icles in the food stream are forced past the filaments into the exhalant 



Rejection 

 current 



Rejection 

 current 



Diaphragm 

 rrying 

 fibular 



ted 

 roove 



Epistome 

 Oesophagus 



Rectum 



l/en tral lip 

 of mouth 



(b) 



Fig. 5.7. Ciliary Feeding in an Endoproct Loxosomella 



(a) Lateral view of animal, showing direction of feeding currents ; (b) ciliary currents, 

 and direction of beat of lateral cilia on tentacles (tiny arrows) (from Atkins, 1932.) 



chamber, while light particles accumulate on the brachial membrane and 

 are thrown into a brachial groove by the action of cilia on the brachial lip. 

 From the groove the food particles are carried to the mouth. Selection of 

 particles, accordingly, is on the basis of size and weight (87). 



Molluscs. Ciliary feeding devices are highly developed in lamellibranchs 

 and certain gastropods, in which they have independently evolved. They 

 have been intensively studied, especially in lamellibranchs, and for detailed 

 accounts the reader is referred to papers by Orton, Yonge and Atkins 

 (see 111). 



Ciliary feeding in prosobranch gastropods has developed independently 

 in at least six families. Of these the Calyptraeidae (Calyptraea and 

 Crepidula) are the most specialized, and feed by sifting out diatoms and 

 other fine plankton material by means of a modified ctenidium. In the 

 sedentary slipper-limpet Crepidula fomicata, the mantle cavity is divided 

 into two lateral chambers, one ventrolateral, the other dorso-lateral, by a 



