On examining a sample of tanaids from the bathybenthos of the Rockall Trough, part of an extensive collection made by the Scottish Marine Biological Association (S.M.B.A), some very thin translucent tubes were noted. In these could be discerned several tanaids, one of which was extremely elongate. These proved to belong to a new genus, the adults of which were even more filiform than Filitanais moskalevi Kudinova-Pasternak, 1973. Scrutiny by the authors of other Rockall Trough samples has resulted in more adult specimens of this remarkable new tanaid being obtained. In this paper it is diagnosed and described, together with a discussion of its biology.