On Pelagiana trichodesmiae n.gen., n.sp., family Pandeidae, (Anthomedusae/Athecatae, Cnidaria), a new hydrozoan associated with the planktonic cyanophyte Trichodesmium thiebautii

Abstract

A new athecate hydroid and its young medusa are described, the hydranths of which are commonly found embedded in colonies of the planktonic blue-green alga Trichodesmium thiebautii Gomont in the tropical and subtropical Atlantic. The hydroid and its medusa, named Pelagiana trichodesmiae n.gen., n.sp., are placed tentatively in the family Pandeidae (order Anthomedusae/Athecatae) because of the structure of the medusa and the one circle of filiform tentacles on the hydroid. The medusa is known only from one specimen which was 0.3 mm wide and 0.4 mm high immediately after release. It is deep bell shaped with a stomach one-third of the subumbrella and two marginal tentacles with large triangular marginal bulbs.