Oswaldella grandis Peña Cantero, Svoboda and Vervoort, 1997

Peña Cantero, A. L. & Vervoort, W., 2004, Species of Oswaldella Stechow, 1919 (Cnidaria: Hydrozoa: Kirchenpaueriidae) from US Antarctic expeditions, with the description of three new species, Journal of Natural History 38, pp. 805-861 : 833-835

Oswaldella grandis Peña Cantero, Svoboda and Vervoort, 1997

( figure 9)

Oswaldella grandis Peña Cantero et al., 1997: 363–367 , figures 7, 14C, D; Peña Cantero and García Carrascosa, 1998: 179; 1999: 212 et seq.; Peña Cantero and Vervoort, 1998: 36; Peña Cantero and Marques, 1999: 85.

Oswaldella bifurca: Peña Cantero, 1991: 175 , pl. 32; Peña Cantero and García Carrascosa, 1994: 125, figure 8 d–f; 1995: 101–104, figure 45A–E.

? Oswaldella bifurca: Naumov and Stepan’yants, 1962: 98; Stepan’yants, 1979: 112, pl. 21 figure 4; Blanco, 1984: 43, pl. 39 figures 89, 90, pl. 40 figures 91–93, pl. 41 figure 94.

Material examined. 702/464, one stem ca 145 mm high ( USNM 1003327); 702/465, two stems up to 500 mm high ( USNM 1003328; RMNH-Coel. 30213); 721/776, four stems up to 460 mm high, with gonothecae ( USNM 1003329; RMNH-Coel. 30214; MNCN 2.03 / 234).

Description. Colonies consisting of polysiphonic and unbranched stems up to 500 mm high. Hydrocaulus divided into internodes, occasionally so in Stn 702 / 465, and provided with alternately arranged apophyses, forming two longitudinal rows in one plane. Cauline apophyses directed upwards, forming an angle of ca 45 ° with long axis of stem and provided with four nematophores ( figure 9B): two axillary nematophores emerging through simple perisarc holes and two more emerging each through a ‘mamelon’, placed laterally on upper surface of apophysis. Cauline apophyses supporting branched hydrocladia; up to third-order hydrocladia observed ( figure 9A). Hydrocladial arrangement symmetrical ( figure 9A); first hydrocladial internode giving rise to two secondary hydrocladia that usually support two or more third-order hydrocladia. No distinct node between cauline apophyses and hydrocladia, although present in the material from Stn 702 / 465. Top of distal hydrocladial internodes truncated.

Hydrocladia homomerously divided into hydrothecate internodes, each provided with one hydrotheca and two nematophores ( figure 9 C–F): one mesial superior emerging through a perisarc hole situated behind free adcauline hydrothecal wall and one mesial inferior provided with a much-reduced nematotheca and emerging through a perisarc hole situated on a slight elevation of internode.

Hydrotheca shallow, situated on distal half of internode ( figure 9 C–F). Adcauline hydrothecal wall almost completely adnate; aperture circular and approximately perpendicular to long axis of internode; rim even. Abcauline hydrothecal wall straight; angle with internodal long axis very acute.

Female gonothecae present ( figure 9G), inserting on infrathecal elevation of hydrocladial internodes, large, club-shaped and provided with a subterminal aperture.

Remarks. Oswaldella grandis is a well-characterized species, easily recognizable by the large, unbranched stems, the shape of the hydrotheca which is placed on the distal half of the hydrocladial internodes, the much-reduced nematotheca, the shape of the gonothecae and the presence of four nematophores on the cauline apophyses, two of which emerge through ‘mamelons’ (cf. table 1).

Ecology and distribution. Oswaldella grandis appears to be a shelf species, having been found at depths of 220 to 440 m on muddy bottoms and on bottoms with small stones (Peña Cantero et al., 1997); our material comes from 109 to 154 m. It is used as a substratum by other hydroids ( Billardia sp.) (Peña Cantero et al., 1997). It has been collected with gonothecae in January and February (Peña Cantero et al., 1997); our fertile material was found in January.

Oswaldella grandis seems to be endemic to West Antarctica (Peña Cantero and Vervoort, 1998). It is known from off Elephant Island (Peña Cantero and García Carrascosa, 1995) and off the south coast of the Weddell Sea (Peña Cantero et al., 1997). Our material was collected off Deception Island, in the South Shetland Islands.