Oswaldella tottoni Pena Cantero & Vervoort 1996

Oswaldella tottoni Peña Cantero & Vervoort, 1996

(Fig. 6)

Oswaldella tottoni Peña CanTerO & VerVOOrT, 1996: 139–142, fig. 2; 1998: 37; 2004: 850; Peña CanTerO et al., 1997: 380–383, fig. 12; Peña CanTerO & García CarrascOsa, 1998: 179; 1999: 214; Peña CanTerO & Marques, 1999: 85; GOnzález MOlinerO & Peña CanTerO, 2015: 439; Peña CanTerO, 2017: 60.

Oswaldella bifurca —TOTTOn, 1930: 208–209, fig. 50.

Material examined. German Antarctic expedition Polarstern ANT XV/3, Stn 48-194, 16 February 1998, 71°14.1’S, 12°27.7’W (Kape Norvegia), 244–246 m, a few stems, up to 120 mm high, with gonothecae.

Description. Polysiphonic, branched stems up to 120 mm high. Stems not divided into internodes, with two longitudinal series of cauline apophyses. Angle between cauline apophyses and stem ca. 45°. Cauline apophyses with two axillary nematophores, each emerging through a simple hole in perisarc (Fig. 6B); no ‘mamelons’ present.

Hydrocladia bifurcated (Fig. 6A), only hydrocladia of second order present. Secondary hydrocladia distinctly bent inwards. First hydrocladial internode bifurcated (Fig. 6A–B), with two similar prongs; frequently without node between prongs and first internode of secondary hydrocladia (Fig. 6A). Mesial-inferior nematophore emerging from a swelling at proximal third of internode (Fig. 6C–E), and provided with a reduced claw-shaped nematotheca (Fig. 6C–E); first hydrocladial internode frequently without nematophore (Fig. 6B). Hydrotheca placed on distal half of internode (Fig. 6A, C–D). Hydrotheca low, about as high as wide (Fig. 6A, C–D). Abcauline hydrothecal wall straight, but distinctly directed outwards (Fig. 6D). Hydrothecal aperture circular, perpendicular to longitudinal axis of internode (Fig. 6C) or leaned adcaudally (Fig. 6D); rim even (Fig. 6C–D). Internode above hydrotheca with distinct longitudinal groove (Fig. 6C).

Gonotheca fusiform with subterminal aperture (Fig. 6F).

Remarks. The stems of this species are polysiphonic only at the base. Branching is also restricted to the most basal part, giving the aspect of rooted tufts with stems mostly unbranched.

The SEM study has confirmed the presence of two axillary nematophores on the cauline apophyses, as already known from previous descriptions (Peña Cantero & Vervoort 1996; Peña Cantero et al. 1997). The nematophores are not provided with the short collar-shaped nematotheca observed in other species of the genus (e.g. O. laertesi see fig. 9B in González Molinero & Peña Cantero 2015).

The groove present on the internode above the hydrotheca seems to be related to the mesial superior nematophore. The adcauline hydrothecal wall is practically adnate in its whole length, so the groove would facilitate the nematophore emergence.

Distribution. Circum-Antarctic (Peña Cantero & Vervoort 2004).