922 PROTOZOA AND OTHER ANIMALS 



Powers (1933a) discussed the possibility that Cryptochilidium echini 

 (Maupas), abundant and universal in Strongylocentrotus lividus at 

 Naples, is a true parasite. In several instances the body was found partly 

 embedded in the intestinal mucosa. As he probably recognized later, 

 this observation does not constitute adequate proof for his conclusion. 

 The genus Cryptochilidium, together with Biggaria, Kahl's genus for 

 some of the forms described as Cryptochilidium, is well represented in 

 sea urchins of all regions. 



Metopus histophagus Powers, as the species name indicates, contains 

 in its food vacuoles epithelial cells from the intestine of its host ( Powers, 

 1935); but it was not observed to cause lesions, and probably simply 

 ingests cellular debris, as does M. circumlabens (Lucas, 1934). The 

 species occurs only in Clypeaster suhdepressus of Tortugas. The species 

 M. circumlabens Biggar occurs in a number of hosts at Bermuda, Tor- 

 tugas, Amoy, and Japan, but several other species seem to have a limited 

 host-specificity. 



Questions of host-specificity and geographical distribution of the 

 ciliates have been discussed by Powers (1935, 1937). He remarked that 

 there is little evidence of rigid host-specificity. Species differ in that re- 

 spect. Yagiu (1935) found Cryptochilidium echini and Anophrys 

 elongata in all but one of the host species, examined by him at Yaku 

 Island, which contained any ciliates; and Powers (1935) found Crypto- 

 chilidium bertnudense [=Biggaria bermudense) and Anophrys elongata 

 in all sea urchins at Tortugas that were infected with ciliates. Nor are 

 those ciliates limited to those regions; they have been found in various 

 localities. There are some ciliates that have been found in only one or 

 a few hosts, these being sometimes in one region only but also some- 

 times in widely separated localities. There is nothing, however, which 

 leads us to expect that, with the accumulation of more data, most or all 

 of them will not be known to be in various hosts in various parts of the 

 world. There is no limitation to certain genera or other taxonomic groups 

 of sea urchins, as would occur in evolutionary development of associa- 

 tions with strict specificity. Though no experimental work has been 

 done, it seems likely that cross infection would ordinarily be easy to 

 accomplish; nevertheless it is noteworthy that given species have char- 

 acteristic faunules, and there are a few sea urchins with no faunules, 

 facts that call for experimental investigation of the host relationships. 



