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 sp. ( Figs 15 , 16 P, 18H, 20H) Material examined. New Zealand Antarctic Expedition TAN0402: Stn 178 , Tangaroa , 27 February 2004 , 71°31’89’’– 71°32’16’’S , 171°18’31’’– 171°18’70’’E (Cape Adare, Ross Sea), 343– 348 m . Description. Monosiphonic, unbranched stems, up to 100 mm high, divided into internodes. Cauline apophyses with two axillary nematophores, each emerging through simple hole in perisarc ( Fig. 15 B). Hydrocladia usually bifurcated, first hydrocladial internode giving rise to two secondary hydrocladia; however, a third-order hydrocladium is not uncommon ( Fig. 15 A). First hydrocladial internode bifurcated, with two similar prongs ( Fig. 15 A). Mesial inferior nematophore emerging from marked swelling at proximal third of internode ( Fig. 15 C); with well-developed, claw-shaped nematotheca ( Fig. 15 C–E). Hydrotheca low, about as high as wide, placed on distal half of internode. Abcauline wall straight; adcauline one mostly adnate ( Fig. 15 C). Hydrothecal aperture circular ( Fig. 15 D), roughly perpendicular to longitudinal axis of internode ( Fig. 15 C); rim even. Gonothecae unknown. Remarks. Our material is undoubtedly conspecific with the material described as Oswaldella sp.2 by Peña Cantero & Vervoort (2004) . It is also morphologically very close to Oswaldella incognita (cf. Figs 8 , 15 ), sharing many characteristics with this species (see also Peña Cantero & Vervoort 2004 ). The number of axillary nematophores, and the absence of 'mamelons', gives to the cauline apophyses of Oswaldella sp. a similar configuration to that found in O . incognita . Additionally, they share the presence of mesial inferior nematotheca, as well as the shape of nematothecae and hydrothecae. Peña Cantero & Vervoort (2004) indicated that Oswaldella sp.2 has longer hydrocladial internodes and shorter hydrothecae and that they also differ in the fact that only secondary hydrocladia had been described for O . incognita . Peña Cantero & Vervoort (2009) , however, studied material of O . incognita with occasional presence of third-order hydrocladia. In our opinion, Oswaldella sp. and Oswaldella incognita share so many key features they are likely conspecific, though it would be necessary to examine the material studied by Peña Cantero & Vervoort (2004) to confirm that the axillary nematophores do not have nematothecae.