SEM study of species of Oswaldella Stechow, 1919 (Cnidaria, Hydrozoa, Kirchenpaueriidae), with an annotated checklist of the species of the genus Author Molinero, A. González Author Peña Cantero, A. L. text Zootaxa 2015 4052 4 401 441 journal article 10.11646/zootaxa.4052.4.1 93f6d085-8e63-4d1e-89c1-f950128b2a61 1175-5326 245887 47EF6E9D-9064-4899-B3DD-276FF7C969EB Oswaldella niobae Peña Cantero & Ramil, 2006 ( Figs 10 , 16 J, 18B, 20B) Material examined. Spanish Antarctic Expedition GEBRAP 95: Stn 5 , 1 January 1997 , 62°52’40’’– 62°52’58’’S , 59°59’07’’– 59°58’02’’W (Bransfield Strait), 699–922 m ( MNCN 2.03/342). Description. Monosiphonic, unbranched stems, up to 68 mm high, divided into internodes. Cauline apophyses with one ( Fig. 10 C) or two axillary nematophores ( Fig. 10 B), each emerging through simple perisarc hole, and, usually, an extra nematophore emerging from ‘mamelon’ ( Fig. 10 B). Hydrocladia unbranched ( Fig. 10 A) or bifurcated. First hydrocladial internode bifurcated, with two similar prongs. Mesial inferior nematophore emerging from marked swelling at basal half of internode ( Fig. 10 E); without nematotheca ( Fig. 10 D–E). Hydrotheca situated on distal half of internode ( Fig. 10 A, D–E). Hydrotheca low, as high as wide. Abcauline hydrothecal wall straight, angle with long axis of internode ca. 45°. Adcauline wall mostly adnate. Hydrothecal aperture circular, slightly tilted downwards ( Fig. 10 E). Male gonotheca fusiform, with subterminal aperture. Remarks. Sometimes, there is an intermediate athecate internode following cauline apophyses ( Fig. 10 A). Athecate intermediate internodes have even been observed between thecate internodes (cf. Peña Cantero & Ramil 2006 ). In the material examined there is variability in the number of nematophores of the cauline apophyses. There can be one or two axillary nematophores. In addition, although typically there is one conspicuous ‘mamelon’, it is absent in some apophyses ( Fig. 10 C).