620 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The modern method of distributing the material brought up by the dredge 

 or gathered by shore collectors immediately among the different phyla represented, 

 resulting from the almost complete extinction of the " naturalist " with a broad 

 zoological knowledge and the appearance of the " specialist " interested only in 

 some one circumscribed group, has rendered exceptionally difficult the study of 

 the ecology of the various marine types. One is constantly reading descriptions 

 of new species which are undoubtedly commensals, in which not the slightest 

 reference is made to any host. Any collection of crinoids received from the East 

 Indian region is certain to include not only myzostomes, but also many other 

 commensals preserved with the crinoids, and the liaison between the latter and the 

 animals in the containers with them should never be broken until it is definitely 

 determined whether or not there is an ecological relationship between them. 



The development of the study of the commensals found with the crinoids has 

 been largely by a series of short notes casually intercalated in papers dealing with 

 crustaceans, ophiurans, annelids, etc., in which a species is said to have been found, 

 upon a oomatulid, but there are a few records of commensalism properly identified 

 as such. 



In a letter written during the cruise of the Challenger by R. von Willemoes- 

 Suhm, one of the Challenger party, to Prof. C. Th. E. von Siebold, and published 

 by the latter in 1876, Willemoes-Suhm says that in 1874 in the Arafura Sea he 

 once examined 80 specimens of a large comatulid and found on about every tenth 

 one a myzostome, the largest he had ever seen. The myzostomes lay or crawled 

 snake-like on the calyx, but seldom in the ambulacral grooves of the arms. Usually 

 there were two or three large ones, and with them a smaller. All these myzostomes 

 were, like the comatulids themselves, mottled with black and white, and all the 

 other parasites of the comatulids showed the same coloration. The other parasites 

 were first, ophiurans clinging to the calyx; second, small aphroditaceans ; third, 

 amphipods which had bored into the disk; and fourth, an apheid. Including the 

 myzostomes, there were thus five parasites on this very large comatulid. 



The large black and white comatulids were probably Zygometra microdiscus 

 or Z. elegans. Carpenter and Potts have suggested that Comatula rotalaria and 

 C. Solaris were probably the species in question, but neither of these was taken at 

 the station in the Arafura Sea, and neither is ever black and white. The myzos- 

 tomes were Mysostomum horologium, the ophiurans were Ophiomaza, the aphro- 

 ditaceans Polynoe, the amphipods probably Laphystiopsis, and the alpheids 

 Synalpheus. 



In his account of Alpheus comatularum published in 1882 Prof. William A. 

 Haswell states that they were invariably found clinging to the arms of a species 

 of comatulid to which their markings gave them a general resemblance. Other 

 commensals of these comatulids were Galathea deflexifrons, and an undescribed 

 species of cymothoid, the latter usually ensconcing itself in the alimentary canal 

 of its host, in which it remained buried with the exception of the anterior third 

 of its body. 



In his monograph on the stalked crinoids, published in 1884, P. H. Carpenter 

 mentions as internal parasites of the group the suctorial crustacean described by 



