308 ECHINODERMS OF THE BRITISH ISLES 



l)()(ly-r()(l.s. Ill tlic II. stage it lias epaulettes at the base of the 

 postoral and ])()stero - dorsal arms; hui how to distinguish it 

 from the II. stage of the Psammechinus miliaris larva, which 

 has likewise epaulettes only at the base of the four main arms, 

 we cannot see in the present stage of our knowledge. 



It is a littoral form, often found on rocky shores ; it bores 

 holes in the rocks, and great numbers usually are found together, 

 each in its hole, the rocks being quite honeycombed by them.^ 

 Also among Zostera they may occur in great numbers. 

 They often cover themselves with fragments of Zostera leaves 



Fig. 177. — Larva of Paracentrotus lividus. (After Joh. Miiller, 

 IV. Abhandl. iiber Echinod. larven.) 



a. From the ventral side ; h, lialf from the dorsal side. 



and the like, thus hiding themselves. In the Mediterranean 

 countries this species is highly esteemed as food, and an 

 important fishery is based on it (and also on Sphcer echinus 

 granulans). Various Infusorians are found parasitic in this 

 Echinoid : Anophrys echini di Mauro and Cryptochilum echini 

 Maupas in the intestine, Colpidium echini Russo in the rectum ; 

 also the Planarian Syndesmis echinorum occurs in this species. 



In British seas this species is common on the south and west 

 coasts of Ireland, and has also been found on the Devon and 

 Cornwall coasts (Ilfracombe, Falmouth). It is elsewhere dis- 

 tributed along the European coasts from the Channel to the 



1 In the Clare Island Survey, Part 67, PI. III. (R. Southern, " Marine 

 Ecology ", Proc. R. Irish Acad., xxxi., 1915), is given a very fine representa- 

 tion of a colony of these rock-boring sea-urchins. 



