214 



THE BIOLOGY OF MARINE ANIMALS 



pedal gland in Vermetus, and by the propodium in Capulus. The latter 

 structure is an anterior extension of the foot, to which food particles are 

 conveyed from the mantle cavity and from which they are collected by a 

 grooved proboscis. An interesting variation is the development in 

 Stephopoma of a sweeping mechanism for supplementing collection of 

 particles within the mantle cavity. The long anterior filaments of the gill 

 are extended and drawn through the water like a sweep-net, and any 

 particles encountered are trapped in the mucus which coats the filaments 

 (52, 76, 110, 115). 



Shelled pteropods (opisthobranchs) are another group of gastropods 

 making use of ciliary feeding (Fig. 5.10b). In Limacina, for example, 



Food pouch 



Outward tract 



Food 

 channel 



Endostyje* 

 and ciliated 



Visceral 

 mass 



Ciliated 

 field 



V.sceral 

 mass 



Shell 



Fig. 5.10a. Feeding Mechanism of the Slipper-limpet Crepidula fornicata 



Animal removed from its shell and mantle turned over to the left. From the endostyle 

 at the base of the gill, mucus and food particles are lashed on to the gill filaments. (From 

 Orton, 1914.) 



Fig. 5.10b. Feeding Mechanism in a Thecosomatous Pteropod Cavolinia in- 



flexa (x 3 1) 

 Arrows on wings indicate directions of ciliary currents. (After Yonge, 1926.) 



feeding currents are created by the beating of cilia in the mantle cavity. 

 Food particles falling out of the stream become entangled in mucus and are 

 carried by ciliary tracts to the mouth. Some collecting is also carried out by 

 the foot. Pallial feeding has been lost in higher pteropods, and feeding is 

 carried out by ciliated fields on the wings and lateral and median lobes of 

 the foot (Cavolinia, CymbuUd). These animals feed on smaller members of 

 the plankton, e.g. diatoms, protozoa, crustacean larvae, etc. (70, 77). 



Lamellibranchs. The majority of lamellibranchs feed on particulate 

 matter, which they filter by means of ciliary mechanisms on gills and 

 labial palps. The ctenidia typically take the form of folds of the body wall, 

 which are suspended in the mantle cavity and which divide the latter into 

 two chambers (Figs. 4.4, 5.11). Water currents created by cilia on the gills 

 enter the ventral or inhalant chamber, pass through slits in the gills and 



