Genus Synhalcurias Carlgren, 1914

Synhalcurias Carlgren, 1914: 53; Carlgren, 1918: 27; Stephenson, 1922: 260; Carlgren, 1949: 19.

Diagnosis. Column cylindrical, distally not expanded, nor forming lobes; with many simple tentacles. Mesenteries 68 to ca. 100, all mesenteries perfect and fertile. After formation of ten first pairs of mesenteries (1st and 2nd cycles), further mesenterial formation cyclical in each of eight lateral endocoels, similar to Halcurias . Two siphonoglyphs. Column ectoderm with or without small nematocyst batteries. Cnidom: basitrichs, spirocysts, microbasic b -mastigophores, microbasic p -mastigophores (each in all tissue). (Modified from Uchida [2007], changes in bold)

Type species. Synactinernus elegans (Wassilieff, 1908)

Remarks. Synhalcurias has been recognized as monotypic since it was established by Carlgren (1914) (see also Carlgren, 1949; Fautin, 2016). In this study, we describe a second species for this genus, S. kakahui sp. nov. To incorporate this additional species, we rearranged the diagnosis as below: 1) adding the cnidom; 2) added the case that not nematocyst batteries in the column; 3) revised that all mesenteries perfect (instead of “almost all”).