Ischnomesus Richardson, 1908

Kavanagh, Fiona A., Frutos, Inmaculada & Sorbe, Jean Claude, 2015, Ischnomesus harrietae sp. nov., a new benthic asellote (Crustacea: Isopoda: Ischnomesidae) from bathyal bottoms of the southern Bay of Biscay, Zootaxa 3911 (2), pp. 201-217 : 203

Ischnomesus Richardson, 1908

Ischnosoma: G. O. Sars, 1868: 84 .

Ischnomesus: Richardson, 1908: 81 ; Hansen, 1916: 56; Gurjanova, 1932: 40 l; Wolff, 1956: 88; Menzies, 1962: 111; Wolff, 1962: 73; Menzies & George, 1972: 971; Kussakin, 1988: 419; Merrin & Poore, 2003: 290 .

Rhabdomesus: Richardson, 1908: 81 .

Bactromesus: Wolff, 1962: 83 .

Type species: Ischnosoma bispinosum G. O. Sars, 1868 (by monotypy).

Species included: Ischnomesus anacanthus Wolff, 1962 ; I. andriashevi Birstein, 1960 ; I. antarcticus Schultz, 1979 ; I. armatus Hansen, 1916 ; I. bacilloides (Beddard, 1886) ; I. bacillopsis (Barnard, 1920) ; I. bacillus (Beddard, 1886) ; I. bidens Menzies, 1962 ; I. birsteini Wolff, 1962 ; I. bispinosus ( G. O. Sars, 1868) ; I. bruuni Wolff, 1956 ; I. calcificus Menzies & George, 1972 ; I. caribbicus Menzies, 1962 ; I. carolinae Chardy, 1974 ; I. chardyi Kussakin, 1988 ; I. decemspinosus Menzies, 1962 ; I. elegans Menzies, 1962 ; I. elongatus Birstein, 1963 ; I. fragilis Birstein, 1971 ; I. glabra Kensley, 1984 ; I. gracilis (Birstein, 1960) ; I. justi Merrin & Poore, 2003 ; I. latimanus Birstein, 1971 ; I. magnificus Menzies, 1962 ; I. multispinis Menzies, 1962 ; I. norvegicus Svavarsson, 1984 ; I. paucispinis Menzies, 1962 ; I. planus Wolff, 1962 ; I. profundus Hansen, 1916 ; I. roseus Wolff, 1962 ; I. simplex Menzies & George, 1972 ; I. simplissimus Menzies, 1962 ; I. spaercki Wolff, 1956 ; I. tasmanensis Merrin & Poore, 2003 ; I. vinogradovi Birstein, 1963 and I. wolffi Menzies, 1962 .

Diagnosis. Pereonites 5–7, pleonite 1 and pleotelson freely articulating. Antennula of at least 6 articles. Maxillipedal palp width equal to or wider than basal endite. Pereopod I carpus with weakly expanded palm. Uropods uniramous, biarticulate.

Remarks. The freely articulating posterior pereonites, pleonite 1 and pleotelson observed in Ischnomesus is a condition presumed to be plesiomorphic, with other genera showing various degrees of fusion of the pereonites (e.g. pereonites 5–7 and pleotelson fused together in genus Haplomesus ; see Kavanagh & Wilson 2007). Uniarticulate uropods have been described by Merrin & Poore (2003) for Ischnomesus justi . As this species displays all the other diagnostic characters that characterise Ischnomesus , biarticulate uropods may not be a diagnostic character for the genus. However, as all remaining 35 species and I. harrietae sp. nov. possess uropods with two articles, we have retained it as a generic character until further information on the occurrence of uniarticulate uropods becomes available through the description of additional species.