104 

 A NEW GYMNOBLASTIC HYDROID. 



By J. H. EOBSON. B.SC. 



A new species of Gymnoblastic Hydroid, which has not been 

 assigned to any existing genus, was discovered at Cullercoats in 

 1914 ; it mil probably be necessary to create for it a new genus, 

 which, however, cannot be done satisfactorily until the adult 

 medusoid has been obtained. At present the medusoid has only 

 been observed in a very young state, but as the observations on 

 the hydroid form are fairly complete, I give here a description and 

 drav;ings of the latter (Plate II.). 



The characteristics of the genus will probably be : — 

 Stem simple, unbranched, rooted by a reticulated stolon, 

 invested by a thin perisarc. Zooids entirely naked, elongated, 

 shaped much Hke a " ninepin," with a single verticil of filiform 

 tentacles round the base of a conical proboscis Gonozooid a 

 free-swimming medusa (incompletely observed.) 



Description of the Species. 



Stem. — Erect, simple, unbranched, the finest specimens 0"5 cm. 

 in height ; rooted by a stolonic network. Perisarc smooth, 

 occasional^ with a few irregular "sviinkles, extremely thin and 

 transparent, mth the milky- white coenosarc showing through its 

 colourless walls. 



Hydranth. — White, long and slender ; the proximal half 

 attenuated, swelling out gradually into a large stomach region, 

 which is sej)arated from the conical h^^ostome by a constriction 

 below the tentacles (Plate I.). 



Tentacles. — Filiform, irregularly studded with large oval 

 thread cells ; 10-20 arranged in a single verticU ; when fully 

 extended they are alternately elevated and depressed, and then 

 appear to be in two circlets. 



Hypostome. — Conical when at rest. The mouth opening 

 generally appears as a small round aperture, but I have seen it 

 expand for a few seconds, closing again rapidly ; when expanded 

 the mouth showed seven well-defined lobes in several cases, and these 



