OPHIUROIDEA 151 



able to throw off their arms when hurt or when anything 

 merely takes hold of them. Some species propagate by self- 

 division, the disk being divided across the middle ; each half 

 then regenerates the lacking part of the disk and the lacking 

 arms, two new individuals being thus formed. This way of 

 propagating is especially common in the genus Oj^hiactis, 

 e.g. the Mediterranean Ophiactis virens and the North Atlantic 

 0. nidarosiensis . 



Parasites are not numerous in Ophiuroids. Some Infusoria 

 may be found in the stomach of Ophiura Sarsi (and probably other 

 species) ; in the genital orgsmsoi Amphipholis squamata the remark- 

 able parasite Rhopalura is found, a primitive worm of the group of 

 Mesozoa, peculiar through the entoderm consisting of only one 

 or a few cells. A remarkable, but hitherto undescribed, parasitic 

 organism is found in the gonads of Ophiura Sarsi, possibly a very 

 much reduced Planarian. Parasitic snails have been found on a 

 few Ophiuroids {e.g. Ophiactis ahyssicola), but are on the whole 

 rare. In Gorgonocephalus caput-mediisce (and other species) a very 

 interesting parasite, Protomyzostoma, a relative of the Myzostoma 

 infesting Crinoids, lives in the body cavity ; it is a centimeter- 

 long flat, red sac, filled up by an immense number of small eggs, 

 and was, in fact, at first described as the genital organs of the 

 Gorgonocephalus. Also the true Myzostoma has been recorded 

 in a few cases from Ophiuroids {Ophiacantha vivipara, Astroceras 

 pergamena, Ophiocreas). In Ophiura albida lives a Trematode, 

 Fellodistomumfellis (Olsson), the sexual stage of which is found in 

 the gall-bladder of Anarrhichas, which must therefore be infected 

 through eating the Ophiuroid. Also a few Cercarias and young 

 Nematods have been found in Ophiuroids. A few Crustaceans are 

 found parasitic in Ophiuroids, viz. the very much transformed 

 Philichthys amphiurce Herouard, in the bursae of Amphipholis 

 squamata, a somewhat less transformed species, Chordeumium 

 obesum (Jungersen), in the gonads of Asteronyx loveni ; further, 

 a related form which produces galls in the epidermis of a tropical 

 Ophiuroid. Also in Ophiomitrella davigera an (undescribed) 

 parasitic Crustacean occurs, which even completely castrates its 

 host. A semiparasitic Copepod, CanceriUa tubulata Dalyell, occurs 

 on Amphipholis squamata. Finally is to be mentioned a curious 

 instance of a parasitic Green- Alga, Coccomyxa ophiurce Rosen- 

 vinge, occurring very commonly on Ophiura texturata and albida 

 in the Limfjord (Denmark), and also observed on the coast of 

 Bohuslen, Sweden, but not known elsewhere. It lives in the 

 skin of the animal, dissolving the calcareous plates, and may even 



