Oswaldella frigida Peña Cantero & Vervoort, 2004

Molinero, A. González & Peña Cantero, A. L., 2015, SEM study of species of Oswaldella Stechow, 1919 (Cnidaria, Hydrozoa, Kirchenpaueriidae), with an annotated checklist of the species of the genus, Zootaxa 4052 (4), pp. 401-441 : 409

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).

Figures

FIGURE 5. Oswaldella frigida Peña Cantero & Vervoort, 2004. A, hydrocladial branching and disposition of hydrothecae; B, cauline apophysis with axillary nematophore and branched hydrocladium; C, detail of cauline apophysis with axillary nematophore; D – F, unforked hydrocladial internodes (D, F frontal view, E lateral view). Scale bar: 400 µm (A – B), 100 µm (D – F) and 40 µm (C).

FIGURE 8. Oswaldella incognita Peña Cantero, Svoboda & Vervoort, 1997. A, hydrocladial branching and disposition of hydrothecae; B – C, cauline apophyses showing axillary nematophores; D – E, unforked hydrocladial internodes (D lateral view, E frontal view); F, detail of mesial inferior nematotheca. Scale bar: 200 µm (A), 100 µm (C – E) and 20 µm (B – F).

FIGURE 16. Detail of the area from which mesial nematophore emerges. A, Oswaldella bifurca; B, Oswaldella delicata; C, Oswaldella elongata; D, Oswaldella erratum; E, Oswaldella frigida; F, Oswaldella garciacarrascosai; G, Oswaldella grandis; H, Oswaldella incognita; I, Oswaldella laertesi; J, Oswaldella niobae; K, Oswaldella rigida; L, Oswaldella shetlandica; M, Oswaldella stepanjantsae; N, Oswaldella vervoorti; O, Oswaldella sp. Scale bar: 20 µm (A – O).