ANTHdMKDUS.E HYDRICHTHYS. 



67 



Hydrichthys mirus Fewkes. 



Hydrichthys mirus, FEWKES, 1888, Bull. Mus. Comp. Zool. at Harvard Coll., vol. 13, No. 7, pp. 124-232, plates 4, 5, 7 figs.; 

 1888, Ann. and Mag. Nat. Hist., ser. 6, vol. i, p. 364; 1888, Proc. Boston Soc. Nat. Hist., vol. 23, p. 391. HARGITT, 

 1904, Bulletin Bureau of Fisheries U. S., vol. 24, p. 32. 



Medusa. The adult medusa is undetermined, but may possibly be Sarsia flammea. The 

 most advanced medusae reared by Fewkes had the following characters: Bell rounded, 

 without apical projection, and in form somewhat fuller than a hemisphere. Size ( ?) Outer 

 surface of bell besprinkled with nematocysts. Bell-walls of moderate thickness, becoming 

 thinner near the margin. There are 4 long, equally developed, radially situated tentacles, 

 with long, tapering basal bulbs which lack ocelli. The 4 radial-canals are broad and straight 

 and there is a simple, narrow, circular vessel. Manubrium cylindrical and about half as long 

 as the depth of the bell-cavity. Mouth surrounded by 4 simple lips ( :). The entoderm of 

 the manubrium is yellow and orange, while that of the tentacle-bulbs is orange. Other parts 

 of the medusa are colorless. 



Fin. 32. Hydroid of ffyjriehthyi mirus, from Fewkes, 

 in Bull, \fuseurn Comp. Zool. at Harvard College. 



Fish bearing hydroid, and a magnified part of hydroid 

 itself. 



I'oinig medusa. When first detached from the hydroid the medusa has but two diametri- 

 cally opposite tentacles, and is more active in its movements than it is when it acquires four 

 tentacles. This may, however, have been due to the injurious effects of confinement. 



Hydroid. The hydroid was found by Fewkes firmly attached to the side of a small fish, 

 Seriola zonata. The hydroid colony arises from a basal network of tubes which forms a 

 plate-like hydrorhiza embedded under the scales of the side of the fish, upon which it is probably 

 a parasite. This basal network gives rise to tubular gonosomes and also to filiform, flask- 

 shaped bodies, which recall the spiral zooids of Hydractinia, excepting that they appear to 

 have a terminal mouth-opening. 



The medusa-bearing gonosomes are conical and gradually taper from base to summit, 

 where there may be a terminal opening. Irregularly distributed side'branches arise from the 

 main axis of the gonosome, and most of these give rise to medusa-buds. These side branches 

 are usually simple, although occasionally they branch. They are hollow and in communi- 

 cation with the entodermal cavity of the main stem. 



Clusters of medusa-buds in various stages of development arise from the ends of the 

 branches. When set free these medusae have but 2 tentacles, but later 2 more tentacles develop. 



