76 MOLLUSCA PARASITIC ON ECHINODERMS chap. 



ranean, and another species has been noticed by Graeffe ^ on 

 Mclithaca ochracea in Fiji. 



On Ecliinodermata. — {a) Cinnoidea. Stilinacomatulicola lives 

 on Comatula mediterranea, fixed to the outer skin, which it pene- 

 trates by a very long proboscis ; the shell is quite transparent." 

 A curious case of a fossil parasite has been noticed by Eoberts.^ 

 A Cal]/2Jtraea-sh.a'ped shell named Platyceras always occiu'red on 

 the ventral side of a crinoid, encompassed by the arms. For 

 some time this was thought to afford conclusive proof of the 

 rapacity and carnivorous habits of the echinoderm, which had 

 died in the act of seizing its prey. Subsequent investigations, 

 however, showed that in all the cases noticed (about 150) the 

 Platyceras covered the anal opening of the crinoid in such a way 

 that the mouth of the mollusc must have been directly over the 

 orifice of the anus. (Jb) Asteroidea. The comparatively soft 

 texture of the skin of the starfishes renders them a favourite 

 home of various parasites. The brothers Sarasin noticed * a 

 species of Stilifer encysted on the rays of Linclda vndtiformis. 

 Each shell was enveloped up to the apex, which just projected 

 from a hole at the top of the cyst. The proboscis was long, and 

 at its base was a kind of false mantle, which appeared to possess 

 a pumping action. On the under side of the rays of the same 

 starfish occmTed a capuliform mollusc {Tliyca cdoconchd), fur- 

 nished with a muscular plate, whose cuticular sm^face was in- 

 dented in such a way as to grip the skin of the Linclda. This 

 plate was furnished with a hole, through which the pharynx 

 projected into the texture of the starfish, acting as a proboscis 

 and apparently furnished with a kind of pumping or sucking 

 action. Adams and Eeeve^ describe Pilcopsis aster icola as living 

 ' on the tubercle of a starfish,' and Stilifer astericola, from the 

 coast of Borneo, as 'living in the body of a starfish.' In the 

 British Museum there is a specimen of Pileojjsis crystallina ' in 

 situ ' on the ray of a starfish. («) On the brittle starfishes {OjjJiiu- 

 roidea) occur several species of Stiliferina. (d) Echinoiclea. Vari- 

 ous species of Stilifer occur on the ventral spines of echinoids, 



^ Described as a Cijpraca, but no doubt an Ovida or Pedicularia : CB. Baht. 

 Par. V. p. 543. 



- Von Grafr, Z. wiss. Zool. xxv. p. 124. 



" Proc. Amcr. Phil. Soc. xxv. p. 231. 



* Ergch. naturio. Forsch. Ceylon, abstr. in Journ. Eoy. Micr. Soc. (2) vi. p. 412. 



^ Voyage of the Samarang, Moll. p. 69, PL xi. f. 1 ; p. 47, PI. xvii. f. 5. 



