Section IV, 1918 [131] Trans. R.S.C. 



Monohrachium parasitum and other West Coast Hydroids. 

 By C. McLean Fraser, Ph.D., F.R.S.C. 

 (From the Pacific Coast Biological Station, Nanaimo, B.C.) 

 (Read May Meeting, 1918) 



In the material collected during 1915 some species of hydroids 

 merit special notice. None of them are new species, but three of 

 them, Monohrachium parasitum, Thuiaria carica and Lictorella cervi- 

 cornis, have not been reported from the west coast of North America. 

 A fourth species, Plumularia phwmlaroides, has been reported from 

 Alaskan and Californian waters but not from the Vancouver island 

 region and a fifth, Obelia dubia, appeared in colonies, larger than any 

 hitherto described. On account of pre-occupation, a new name is 

 introduced for Thuiaria distans. 



MONOBRACHIUM PARASITUM Mjereschkowsky 



Fig. 1 



Monohrachium parasitum mereschkowsky, Hydroids from the White 



Sea, 1877, p. 226. 

 Monohrachium parasitum levinsen, Meduser, Ctenophorer og Hy- 



droider fra Groenlands Vestkyst, 1893, p. 151. 

 Monohrachium parasiticum bonnevie. Den Norske Nordhavs-Ex. 



1899, p. 51. 



Trophosome. — Colony consisting of many zooids, about 20, 

 growing from a reticulate stolon which appears on the surface of small 

 living shells. The zooids appear at the hinge of the shell but the 

 network extends over the surface to the margin, with a number of 

 free ends projecting beyond it. The terminal iDortion of these free 

 ends consists of a globular mass of large thread cells, or cells having a 

 similar appearance, having no perisarcal protection. They look not 

 unlike the defensive zooids in Hydractima and possibly they may 

 have the same function. The individual zooid is small, 0-7 or 0-8 mm. 

 in height, fusiform, possessing great freedom of movement; the 

 proboscis is approximately half as long as the remainder of the zooid; 

 the mouth is terminally placed, around it thread cells are closely 

 arranged but not in groups; further down on the proboscis they are 

 much less numerous; there is no constriction corresponding to the 



