NUTRITION AND FEEDING MECHANISMS 235 



Acanthodoris, attack ascidians and polyzoans: they cut into their prey with 

 the radula and suck out semi-liquid food by means of a buccal pump 

 (27, 92). 



Jn many carnivorous gastropods the radular apparatus is carried 

 on the end of a long extrusible proboscis which can be inserted into the 

 prey. Thus Cerithiopsis feeds on siliceous sponges by thrusting its long 

 proboscis into the osculum, or through adventitious apertures, to reach 

 the softer parts within. Sycotypus attacks oysters by stealth, waiting until 

 the latter opens up, when it thrusts its shell between the oyster's valves 

 and pushes its proboscis into the soft parts. Whelks {Buccinum, Busycon) 

 force open the valves of lamellibranchs and remove the soft parts of the 

 prey with the aid of the proboscis (Fig. 5.26). Other gastropods bore 



Fig. 5.26. Sycotypus, a Gastropod, Opening an Oyster. (From Ankel (5).) 



through the shells of lamellibranchs by mechanical or chemical means. 

 Urosalpinx and Nucella drill an opening with the radula; Natica liberates 

 a certain amount of free acid (H 2 S0 4 ) from a gland on the proboscis for 

 dissolving a hole in the shell of the prey (Fig. 5.25). In either event the 

 proboscis is pushed through the aperture so made and extracts the soft 

 parts of the prey (14, 15, 29, 32, 51). 



Shipworms Teredinidae obtain much of their nourishment from the 

 wood in which they bore. The wood is rasped away by movements of the 

 shell valves and the scrapings are carried into the mouth by ciliary action 

 (p. 660). In addition a certain amount of plankton is collected by gills and 

 palps. Analyses of amino-acids show that Teredo acquires its dietary-N 

 from both the wood and suspended nannoplankton (33, 56). 



Crustacea. The gribble Limnoria is an isopod which tunnels into wood 

 and feeds on wood particles. Pure wood has a very low protein content, 

 and wood-destroying fungi contribute much amino-N to the diet of the 

 gribble (88a). The habits of these marine borers are further described 

 in Chapter 15 (p. 661). Ligia, the sea slater, browses on sea weeds 

 which are cut up by the mandibles; Idotea, another isopod, is an 

 omnivorous scavenger and scrapes and bites food masses with the mouth 

 parts (79). Some of the littoral gammarids feed on sea weeds, tearing off 

 pieces with the maxillipeds and crushing them with the mouth parts. 



