640 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



DNDBTEBMINED CRDSTACEANS. 



Dr. W. B. Carpenter writes that it is not a little curious that in the specimens 

 of Antedon bifida which, through the kindness of Mr. Charles Stewart, he received 

 from Plymouth Sound, the alimentary canal is frequently almost choked up by 

 the body of a suctorial crustacean with its egg masses. 



He says that as this is far too large and powerful an animal to have been drawn 

 into the mouth by the ciliary current as an article of food, and as its body rarely 

 shows any indication of having been acted on by the digestive power of the crinoid, 

 he is disposed to think that it is introduced either as an egg or as a larva, and has 

 undergone its development parasitically where it is found. 



Encysted in the ventral perisome of the disk of some specimens of Heliometra 

 glacialis which had been cut into sections P. H. Carpenter found the remnants of 

 a parasitic crustacean; but though one or two accomplished zoologists examined 

 the remains he was unable to learn anything about its affinities. 



ECHINODERMA. 



OPHIUKOIDE.V. 



Such of the ophiurans as habitually live clinging to arborescent marine 

 organisms, from which they derive their noiirishment, usually indirectly through 

 the appropriation of food particles collected by and intended for the host, are 

 occasionally to be found upon the crinoids. 



This association, relatively infrequent, appears to be quite fortuitous, excepting 

 only in the case of the species of the genus Ophiomaza; but even these species are 

 occasionally found on other organisms. 



The first ophiuran by habit commensal on a crinoid was described in 1867 by 

 Ljungman under the name of Ophiocnemis obscura; its characteristic commen- 

 salism was not, however, mentioned. 



In 1871 Theodore Lyman established the genus Ophiomasa, describing 0. 

 cacaotica from Zanzibar. 



Speaking of the cirri of the pentacrinites, C. Wyville Thomson wrote in 1873 

 that they have no true muscles, but that they have, nevertheless, some power of 

 contracting around resisting objects which they touch, and there are often star- 

 fishes and other sea animals entangled among them. 



In 1874 Lyman referred Ljungman's Ophiocnemis obscura to his genus Ophio- 

 maza,. In that year R. von Willemoes-Suhm, then on board the Challenger, noticed 

 on large black and white comatulids dredged in the Arafura Sea some ophiurans 

 which he took to be parasitic, and which were of the same color as the hosts. His 

 observation was published in 1876 and was the first suggestion of commensalism 

 between ophiurans and crinoids. 



In 1884 P. H. Carpenter remarked that he had frequently found ophiurans 

 entangled in the cirri of the crinoids (it is not quite clear whether of the comatulids 

 or of the pentacrinites, or of both), and once an ophiuran pluteus attached to a 

 stem fragment of a species of Metacrimts; following Thomson, he considers these 

 associations as probably merely accidental. 



