J^ MOLLUSCA PARASITIC ON ECHINODERMS chap. 



another species has been noticed by Graeffe ^ on Melithaea 

 ochracea in Fiji. 



On Echinodermata. — (a) Crinoidea. Stilina comaMicola 

 lives on Comatula mediterranean fixed to the outer skin, which it 

 penetrates by a very long proboscis ; the shell is quite transpar- 

 ent.2 A curious case of a fossil parasite has been noticed by 

 Roberts.^ A Calyptrea-^Yid^^Qdi shell named Platyceras always 

 occurred 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 investiga- 

 tions, 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. (5) Aster o idea. 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 Llnekia multiformis. 

 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 occurred a capuliform mollusc {Tliyca ectoncha)^ fur- 

 nished with a muscular plate, whose cuticular surface was in- 

 dented in such a way as to grip the skin of the Linckia. 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 Reeve ^ describe Pileopsis astericola as living 

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

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

 British Museum there is a specimen of Pileopsis crystallina 'in 

 situ ' on the ray of a starfish, {c) On the brittle starfishes 

 (Ophiuroidea) occur several species of Stiliferina. (fi) Ecldnoi- 

 dea. Various species of Stilifer occur on the ventral spines of 



1 Described as a Cypraea, but no doubt an Ovula or PecUcularia : CB. Bakt. 

 Par. V. p. 543. 



2 Von Graff, Z. loiss. Zool. xxv. p. 124. 

 8 Proc. Amer. Phil. Soc. xxv. p. 231. 



* Ergcb. natuno. Forsch. Ceylon, abstr. mjourn. Roy. 3Iicr. Soc. (2) vi. p. 412. 

 '' Voyage of the Samarang, Moll. p. 09, PI. xi. f. 1 ; p. 47, PI. xvii. f. 6. 



