Hydromedusae observed during night dives in the Gulf Stream Author Schuchert, Peter Muséum d’histoire naturelle, C. P. 6434, CH- 1211 Genève 6, Switzerland peter.schuchert@ville-ge.ch Author Collins, Richard 880 NE 33 rd Street, Boca Raton, Florida, USA rc6684@icloud.com text Revue suisse de Zoologie 2021 2021-10-21 128 2 237 356 journal article 3356 10.35929/RSZ.0049 172fa5c5-c0c4-4bd7-b710-d608237b8458 0035-418 5639938 8382D1CA-7C0E-4B1C-9591-4CEAA2F296FB Genus Orchistoma Haeckel, 1879 Orchistoma Haeckel, 1879: 138 ; type species Mesonema pileus Lesson, 1843 ( Kramp, 1961 ) . Tetracannota Mayer, 1900: 46 ; type species Tetracannota collapsum Mayer, 1900 by monotypy. Diagnosis: Medusa with short manubrium on large gastric peduncle; mouth with 8-30 sinuous or crenulated lips; eight or more radial canals, simple, ramified, or in groups of four. Up to 64 marginal tentacles; no marginal cirri, but with thin, filiform, tentaculiform structures devoid of marginal bulbs; gonads usually on proximal parts of radial canals; numerous adaxial ocelli; without statocysts, without cordyli, without excretory pores or papillae. Hydroid phase unknown.