OCR Text |
Show 100 MR. E. S. RUSSELL ON A NEW HYDROID. [Feb. 6, at opening of umbrella-cavity. Exumbrella with a few nemato-cysts scattered over it. Yelum well developed. Manubrium, when extended, as long as umbrella-cavity, cylindrical, and wuth narrowed end. Mouth simple, circular, with a ring of bead-like nematocysts closely surrounding it. Four ocellar bulbs, ellipsoid : one of these is somewhat larger than the others. Radial canals four, simple. Dimensions. Length of bell 0*8 mm.; breadth of bell 0*7 m m. Colours. Manubrium tinged with yellow, but very faintly. Ocellar bulbs golden yellow. The type specimen of Trichorhiza brunnea was discovered on June 29th, 1905, clinging to the tentacles of a specimen of Corymorpha nutans Sars, dredged in 17 fath. at Ettrick Bay, Bute, Firth of Clyde. The filiform hydrorhiza with its branches was intertwined among the tentacles of the Corymorpha so as to be with difficulty unravelled from them. The Trichorhiza was kept alive for a day or two at the Millport Marine Biological Station, and gave off on July 1st the medusoid which has been described. It was usually to be seen half-retracted into its protective cup, with the proximal tentacles much contracted, and the distal ones looking like mere knobs. On the rare occasions on which it was observed in an expanded condition, the tentacles of the outer circle were seen to be held rather stiffly extended. Systematic. On account of its possession of two verticils of tentacles, the proximal filiform and the distal capitate, Trichorhiza is to be referred to the family Pennarida? as constituted by Allman (1). That family contained the following genera:- Pennaria Goldfuss, Halocordyle Allman, Stauridium Dujardin, Vorticlava Alder, Heterostep>hanus Allman, Acharadria Wright, and Acaidis Stimpson. Two other genera have sometimes been associated with the Pennarida?, namely Blastothela Yerrill, which is placed among the Pennarida? by Delage et Herouard (3), and Tiarella Schulze, which is referred to the same family by G. Herbert Fowler (4). But such an assemblage of genera by no means makes up a homogeneous family. K. C. Schneider (6), in his critical revision of the classification of Hydroids, has removed Stauridium to his amended family of the Corynida?. Tiarella, with its three rows of capitate tentacles, has also been referred to this extended family of the Corynida? by M m e . Motz-Kossowska (5), who follows Schneider's classification in the main. These two genera are rightly separated from the other genera of Pennarida?, as they have little in common with the Pennarian type. The seven which remain of the nine genera mentioned above are all fairly closely allied to one another. Halocordyle certainly must be united with Pennaria, and we may with Schneider also bring under Pennaria the genera Vorticlava, Acharadria, Acaidis, and Heterostephanus. Ileterostephauus is allied by its medusoid with the Corymorpha type. Blastothela too |