ASSOCIATIONS 



597 



is reduced, whereas the mouth region is enlarged into a disc-like sucker 

 by which the snail adheres to a starfish. Opening into the centre of the disc 

 is a muscular proboscis which is protruded and inserted into the skin of 



Fig. 14.10. Parasitism in Gastropods 

 (a) Thyca ectoconcha, an ectoparasite of starfish {Linckia); (b) Stilifer linckiae, 

 parasitic in starfish ; (c) Gasterosiphon deimatus, parasitic in holothurians ; (d) Entoconcha 

 mirabilis, parasitic in holothurians; (e) E. mirabilis in its host (Synapta). (Redrawn from 

 Nancy, 1913; Ankel, 1936; Caullery (15).) 



the starfish between the calcareous plates. In T. cristallina, for example, the 

 proboscis, when protruded, is three times the length of the body. Other 

 modifications of the gut are discovered in the absence of a radula, and in 

 the presence of a muscular bulb at the end of the proboscis for sucking in 

 the body fluids of the starfish to which the gastropod is attached. 



