New and unusual abyssal gammaridean Amphipoda from the north-east Pacific

Seventeen species of gammaridean amphipods were identified from sediment trap collections in the north-east Pacific, off the central California coast from depths of 3450–4050 m. Four new monotypic genera, Anisocallisoma (Family Scopelocheiridae), Triquetramana (Family Eusiridae), Octomana and Macroarthrus (Family Pardaliscidae) and eight new species, Cyphocaris latirama, Schisturella spinirama, Paracallisoma spinipoda, Anisocallisoma armigera, Triquetramana brevipalpa, Octomana hadromischa, Macroarthrus victoriae, Oedicerina denticulata are described. A number of new and unusual morphological characteristics were discovered, most notably in the family Pardaliscidae, where two of the new genera belong. In addition, new distributional and/or depth records are established for the following species: Procyphocaris indurata (K. H. Barnard, 1925), Scopelocheiropsis abyssalis Schellenberg, 1926a, Rhachotropis distincta (Holmes, 1908), Cleonardo biscayensis Chevreux, 1908b, Cleonardo macrocephala Birstein and Vinogradov, 1955, Pardaliscopsis tenuipalpa Chevreux, 1911, Halice aculeata Chevreux, 1912 and the genus Oedicerina Stephensen, 1931. In order to assist future identification, the new species are fully diagnosed and illustrated. Three tables for comparing characters and a key to the species of Oedicerina are also provided. Additional morphological information and figures are given for existing species that hitherto were poorly described and illustrated. Sediment traps normally employed in studying organic matter fluxes are herewith used for the first time as a source of deep-sea amphipods, and this potentially exciting method is discussed. The high proportion of new taxa illustrates the deficiencies in our knowledge of the abyssal fauna in this area, emphasizes the importance of continued collecting in the deep-sea, and demonstrates the need for increased taxonomic effort to document this diversity.