Haplomesus Richardson, 1908

Merrin, K. L. & Poore, G. C. B., 2003, Four new species of Ischnomesidae (Crustacea: Isopoda: Asellota) from off south-eastern Australia, Memoirs of Museum Victoria 60 (2), pp. 285-307 : 286

Haplomesus Richardson

Haplomesus Richardson, 1908: 81 .— Hansen, 1916: 59.— Gurjanova, 1932: 42.— Birstein, 1960: 6.— Menzies, 1962: 117.— Wolff, 1962: 86.— Birstein, 1963: 59.— Birstein, 1971: 209.— Menzies and George, 1972: 973.— Kussakin, 1988: 445.

Type species. Ischnosoma quadrispinosum Sars, 1879 (by monotypy).

Diagnosis. Pereonites 5–7 fused with pleonites; pleotelson fully fused to pereonite 7. Antenna 1 of 6 articles. Mandible palp absent. Maxilliped palp narrower than basal endite, articles 2 and 3 expanded. Pereopod 1 carpus of subequal width throughout length. Male pleopod 2 stylet does not extend beyond sympod. Uropod moderately short and of 1 article (except Haplomesus franklinae sp. nov. —with 2 articles).

Remarks. In his description of Haplomesus, Hansen (1916) stated that the uropods are of only one article. This is true of all except the new species described below which has two uropodal articles. In Haplomesus franklinae , the presence of biarticulate uropods is treated as a specific autapomorphic character. The fusion of pereonites 5–7 with the pleonites and pleotelson, and the stylet of male pleopod 2 not extending beyond the sympod, are two of the characters which preliminary phylogenetic analysis have shown to be key synapomorphies for this genus (unpubl. data). This analysis also shows that if Haplomesus franklinae were placed in another genus it would render Haplomesus paraphyletic.