Valettietta, a new genus of deep-sea amphipod (Gammaridea: Lysianassidae) with descriptions of two new species from the North Atlantic Ocean Roger J. Lincoln Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD Michael H. Thurston Institute of Oceanographic Sciences, Brook Road, Wormley, Godalming, Surrey GU8 5UB Introduction Within the gammaridean family Lysianassidae the combination of a strongly toothed mandibular incisor and unspecialized gnathopods is shared by only 4 genera, Valettia Stebbing, 1888, Alicella Chevreux, 1899, Valettiopsis Holmes, 1908 and Valettiella Griffiths, 1977. Each is monotypic with the exception of Valettiopsis which comprises 4 species, dentata Holmes, 1908, macrodactyla Chevreux, 1909, anacantha Birstein & Vinogradov, 1963 and multidentata Barnard, 1961. Barnard (1969) included one other genus, Onesimoides Stebbing, 1888, in his key to lysianassids having a toothed incisor, but there is some doubt as to the true nature of the mandibular margin. Stebbing (1888), in his description of O. carinatus says '. . . cutting edge . . . seemingly of the usual form . . .'. In O. cavimanus, the mandible has '. . . bord tranchant presque simple, renforce a chacun de ses angles par des bourrelets de chitine. . . .' (Pirlot, 1933), while in O. chelatus the cutting edge is simple (Pirlot, 1933). Those genera with a strongly dentate incisor share a broadly similar facies and can be regarded as forming a natural group, with the omission of Valettia coheres which has a quite different morphology, especially in the structure of the mouthparts. The choice of names for these genera has turned out to be rather unfortunate since the genus name Valettia was used as the stem term for the later taxa Valettiopsis and Valettiella with which it does not have close affinity. Valettiopsis and its allies live at moderate to great ocean depths and have as a conse-quence been infrequently recorded. In fact, all six species were first described from unique types, and only dentata and macrodactyla have since been redescribed from additional material (Barnard, 1967; Chevreux, 1935). Recent deep-water collections from the North Atlantic made during cruises of RRS Discovery and RRS Challenger have produced 5 mature individuals of this rare lysianassid group, one belonging to Valettiopsis macrodactyla, the other 4 representing two species new to science. The combination of characters shared by the two new species puts them close to Valettiopsis, but with sufficient disparity in the configuration of the coxal plates, pereopodal bases, and mandibular palp armature to justify the erection of a new genus for which we propose the name Valettietta gen. nov. One existing species of Valettiopsis, namely V. anacantha from the Philippine Trench in the Pacific, is transferred to the new genus. Systematics Family LYSIANASSIDAE Genus VALETTIOPSIS Holmes, 1908 DIAGNOSIS. Body robust, compressed, pleosome well developed; urosome segment 1 with Bull. Br. Mus. not. Hist. (Zool.)44(2): 85-101 Issued 24 February 1983
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