342 



MYZOSTOMARIA 



CHAP. 



single family, Myzostomatidae, contains but two genera, Myzostoma 



F. S. Lkt. and Stelechopus 

 v. Gr. 



Some of them move, 

 more or less actively, on 

 the surface of their hosts, 

 others live in a sessile 

 condition between the 

 joints of the arms or pin- 

 nules, causing a greater 

 or less malformation 

 thereof, sometimes leading 

 to the formation of a more 

 or less globular cyst like a 

 plant -gall, due to over- 

 growths of the joint, as in 

 M. deformator v. Gr. and 

 M. cysticola v. Gr.: while 

 M. jpulvinar v. Gr. is endo- 

 parasitic in the intestine. 

 Two species occur on our 

 common Anted on {Coma- 

 tula) rosacea ; one, M. cirriferum Lkt., creeps about the oral surface, 

 especially along the food grooves of the disc and arms ; the other, 

 M. glahrum Lkt., lives close to the mouth of the Crinoid, so that 

 its pharynx can be inserted into the oesophagus of the host ; this 

 species rarely moves from this position, and carries a young one 

 on its back. 



The Myzostomaria are circular or oval, more or less markedly 

 convex dorsally, flat ventrally ; Stelechopus, however, which lives 

 on Hyocrinus, is elongated. The margin of the body is provided 

 with ten or more pairs of cirri, short (M. glahrum) or long (M. 

 cirriferum), and the general appearance of the animal is greatly 

 changed in some species by the great elongation of the hinder 

 cirri, into which the viscera may extend {M. filicauda v. Gr.). 

 On the ventral surface are five pairs of small conical " parapodia," 

 arranged, like the internal organs, in a radiate manner. Each 

 parapodium carries a couple of chaetae ; one a hook, the other 

 serving as a " guide " for this hook. The four " suckers " on 

 each side are either glandular or sensory organs ; and Wheeler 



Fig. 185. Myzostoma glahrum Lkt., on the disc 

 of Antedon rosacea. The hermaphrodite in- 

 dividual {) lies over the mouth of the Antedon, 

 and carries on its back at the anterior end a 

 young one (6) with only male organs fully 

 developed, aj), The anal papilla of Antedon. x 4. 



