Oswaldella frigida Pena Cantero & Vervoort 2004

Oswaldella frigida Peña Cantero & Vervoort, 2004

(Figs 5, 16 E, 17E, 19E)

Material examined. Australian Antarctic Expedition: Stn BTC 0 7, Aurora Australis, 2 January 2010, 64.28 S, 97.12 E (Tressler Bank, off Queen Mary Coast), 708 m (Australian Antarctic Division, Tasmania, Australia, VII 09/10 BTC 07). United States Antarctic Research Program (USARP): Stn 691/26, Hero, 10 February 1969, 63°26’– 63°25’S, 62°15’– 62°14’W (south of Low Island, Antarctic Peninsula), 119–124 m (USNM 1003326).

Description. Monosiphonic, unbranched stems, up to 75 mm high, divided into internodes. Angle between cauline apophyses and stem ca. 45°. Cauline apophyses with one to four nematophores, one or two axillary ones (Fig. 5 B–C), each emerging through bare hole in perisarc, and up to two extra nematophores, each emerging through “mamelon”.

Hydrocladia typically with asymmetrical branching, with main primary hydrocladium giving rise to several second-order hydrocladia (Fig. 5 A). First hydrocladial internode bifurcated, with two unequal prongs (Fig. 5 A–B). Mesial-inferior nematophore emerging from strongly marked swelling at proximal third of internode (Fig. 5 E–F); without nematotheca (Fig. 5 D–F). Hydrotheca placed on middle of internode or at its proximal third (Fig. 5 A, D– F). Hydrotheca low, about as high as wide. Abcauline hydrothecal wall straight or slightly convex. Rim of hydrothecal aperture typically uneven, strongly depressed frontally (Fig. 5 D, F), but even at proximal internodes (Fig. 5 A).

Gonothecae elongated, with large subterminal aperture and diaphragm at basal third.

Remarks. The material examined differs from that described by Peña Cantero & Vervoort (2004: 830) in having a single axillary nematophore, whereas two were described by those authors, who also stated that one, occasionally two ‘mamelons’, were also present. In the material here studied we have observed one ‘mamelon’ or none. This fact points, again, to the existence of some variability in the number of nematophores in the cauline apophyses, particularly in relation to the presence of ‘mamelons’, in some species (see also O. stepanjantsae for example).

Noteworthy is the presence of a sort of ramp in the axillary nematophore of the cauline apophyses (Fig. 5 C). This structure is also present in material examined by Peña Cantero & Vervoort (2004: Fig. 8 C).