ECHINOIDEA 263 



regenerated, but even rather large fractures of the test are 

 healed. Autotomy is not known to occur in the Echinoids. 



Parasites are found in good numbers in Echinoids. Various 

 Infusorians [Colpidium echini Russo, Cryjjtochilum echini Maupas, 

 Anophrys echini Di Mauro) occur in the intestinal canal of regular 

 Echinoids ; Sporozoa may be found in the intestinal wall in 

 Spatangoids. Tavo forms of Nematodes, Oncholaimus echini 

 Leydig and Ichthyonema Grayi Gemmill and Linstow, are known 

 from the body cavity and intestinal canal of Echinus esculentus, 

 also a Planarian, Syndesmis echinorum Shipley, from the same 

 species, and from several other regular Echinoids. In a Japanese 

 Echinoid, Mespilia globulus, a Trematode is commonly found in 

 the gonads. Various Gastropods {Stylifer, Pelseneeria, Mucro- 

 nalia) live boring into the test of Echinoids. Various Copepods 

 are found living on Echinoids, e.g. Astrocheres echinicola Norm, 

 on Echirius esculentus ; one species, Pionodesmodes phormosomce 

 Bonnier, forms internal galls on the test of Hygrosoma Petersii, 

 another, Echinocheres globosus H. J. Hansen, forms galls in the 

 spines of a Pacific Echinothurid, Arceosoma gracile. In a South 

 American Echinoid a small crab Lives in the rectum, causing 

 irregularities in the apical system of this species. Another crab, 

 Zebrida Adamsii White, lives on various tropical sea-urchins, 

 devouring their spines and tube-feet. It is peculiarly strij)ed so 

 as to resemble the spines of the Echinoid on which it lives, a 

 peculiar kind of protective coloration. On a tropical Echinoid, 

 Diadema, with very long, pointed spines, small fishes and shrimps 

 have been observed to seek shelter among the spines. In the 

 Cidarids the spines are often overgrown with foreign organisms, 

 Bryozoans, Hydroids, Sponges, etc. ; such, however, are not to 

 be regarded as parasites ; they only attach themselves to the 

 older spines, where the epidermis has disappeared, as they do to 

 any other hard object. Neither can the mussels {Montacuta) often 

 found among the spines of Spatangus and Echinocardium be 

 regarded as parasites, but only as commensals. The Ostracod 

 Philomedes brenda Baird (Syn. Cypridina globosa Lilljeborg), 

 sometimes occurring round the anus of Strongylocentr. dro- 

 bachiensis, could hardly even be regarded as a commensal. 



Several Echinoids play an important role as food for man in 

 southern Europe and in tropical countries. It is only the genital 

 organs which are eaten, raw or prepared. As food for fishes and 

 other marine animals, the Echinoids are of less importance. 



On account of their solid test the Echinoids are especially 

 adapted for preservation in a fossil state, and they are, in fact, 



