Oswaldella grandis Pena Cantero, Svoboda & Vervoort 1997

Oswaldella grandis Peña Cantero, Svoboda & Vervoort, 1997

(Figs 1–2)

Oswaldella grandis Peña CanTerO, SVObOda & VerVOOrT, 1997: 363–367, figs 7, 14C, D; Peña CanTerO & García CarrascOsa, 1998: 179; 1999: 212 eT seq.; Peña CanTerO & VerVOOrT, 1998: 36; 2004: 833–835, fig. 9; 2009: 86; Peña CanTerO & Marques, 1999: 85; Peña CanTerO & Ramil, 2006: 953, figs 2D, 3A–C; Peña CanTerO, 2008: 457; 2013: 129–130; GOnzález MOlinerO & Peña CanTerO, 2015: 412, 436, figs 7, 16G, 17G, 19G.

Oswaldella bifurca —Peña CanTerO, 1991: 175, pl. 32; Peña CanTerO & García CarrascOsa, 1994: 125, fig. 8d–f; 1995: 101–104, fig. 45A–E.

? Oswaldella bifurca —NaumOV & STepanjanTs, 1962: 98; STepanjanTs, 1979: 112, pl. 21 fig. 4; BlancO, 1984: 43, pl. 39 figs 89, 90, pl. 40 figs 91–93, pl. 41 fig. 94.

Material examined. German Polarstern Antarctic expedition ANT VIII-5: Stn 16-475, 13 February 1990, 76.85°S, 49.43°W (off Ronne Ice Shelf, Weddell Sea), 280 m, single colony c. 170 mm high, with female gonothecae (Holotype, RMNH Coel. no. 27466, three slides no. 3248). Spanish Antarctic expedition GEBRAP 96: Stn 5, 1 January 1997, 62°52’40’’–62°52’58’’S, 59°59’07’’– 59°58’02’’W (Bransfield Strait, off Livingston Island, South Shetland Islands), 922– 699 m, one stem c. 180 mm high, with gonothecae.

Description (Holotype). Polysiphonic, unbranched stem 170 mm high. Angle between cauline apophyses and stem ca. 45°. Cauline apophyses with up to six nematophores, three to four axillary ones (Fig. 1B), each emerging through a simple hole in perisarc, although usually provided with a very short collar-shaped nematotheca (Fig. 1B), and up to two other nematophores, each emerging through a ‘mamelon’, sometimes little marked or even absent (Fig. 1B).

Hydrocladia much branched (Fig. 1A), with up to third-order hydrocladia. First hydrocladial internode bifurcated (Fig. 1A), with two similar prongs. Mesial-inferior nematophore emerging from slightly marked swelling at proximal third of internode (Fig. 1D–E) and provided with a reduced nematotheca (Fig. 1C–E). Hydrotheca placed on distal half of internode (Fig. 1A, C–D). Hydrotheca low, about as high as wide. Abcauline hydrothecal wall straight. Hydrothecal aperture circular, perpendicular to longitudinal axis of internode; rim even (Fig. 1C–D).

Female gonothecae club-shaped, with sub-terminal aperture (Fig. 1F).

Remarks. The SEM study has allowed us to better study the nematophore number and structure of the cauline apophyses. These are relatively short and strongly directed upwards, which makes it really difficult to observe the axillary nematophores. This justifies, for example, that O. grandis was previously characterized as having two axillary nematophores when it actually is provided with three or four. In addition, we observed the presence of short collar-shaped nematothecae associated with the axillary nematophores, as evidenced in other species of Oswaldella (e.g. O. laertesi Peña Cantero, 2007) by González Molinero & Peña Cantero (2015). In the holotype, however, the presence of collar-shaped nematothecae is not constant. There are examples where it is absent, or not completely developed, in one or more of the axillary nematophores. On the other hand, the ‘mamelons’ of the cauline apophyses are sometimes little marked or even absent.

In the material of O. grandis studied by González Molinero & Peña Cantero (2015), the mesial inferior nematophore was deprived of a nematotheca, probably due to the bad condition of the colony. This material also differs from the type material in the fact that the unforked hydrocladial internodes do not present a distinct infrathecal swelling. Concerning the number of nematophores of the cauline apophyses, there were three axillary nematophores emerging through simple holes in perisarc, but there was no collar-shaped nematotheca, perhaps related again to the bad condition of the material. In addition, there were up to two extra nematophores, each emerging through a ‘mamelon’, although they were sometimes absent.

In order to evaluate if these discrepancies could be due to interspecific differences, we studied material ascribed to O. grandis by Peña Cantero & Ramil (2006). This material had been collected during the Spanish Antarctic expedition GEBRAP 96 in an area relatively close to that of the material studied by González Molinero & Peña Cantero (2015). Expecting to find similar characters to those described by González Molinero & Peña Cantero (2015), the GEBRAP material, however, agreed with the type material in every detail. The cauline apophyses also have up to six nematophores, three to four axillary ones, usually with a short collar-shaped nematotheca (Fig. 2B–C), and two other nematophores, each emerging through a well-marked ‘mamelon’ (Fig. 2B–C). Consequently, we consider that the few differences between the holotype and the material studied by González Molinero & Peña Cantero (2015) are likely related to the bad condition of the latter.

As in other species of the genus [see González Molinero & Peña Cantero (2015), and O. terranovae below], the number of axillary nematophores in the cauline apophyses of O. grandis is variable, from three to four. The species was originally posited to be characterized by the presence of two axillary nematophores (cf. Peña Cantero et al. 1997), but that number was clearly underestimated due to the difficulty in observing the axillary nematophores with an optical microscope. See González Molinero & Peña Cantero (2015) for a discussion about the known variability in the number of axillary nematophores in the cauline apophyses in the species of Oswaldella studied using SEM.

There is also variability concerning the “mamelons” of the cauline apophyses. Peña Cantero et al. (1997: 364) characterized the species by the presence of two “mamelons”, but pointed out that “towards distal part of the stem ‘mamelons’ of apophyses tend to become reduced or even absent”. However, they also indicated that circular perisarc holes were always present. In the present study, the variability in the number and development of the ‘mamelons’ has been confirmed. What would be characteristic for the species is the presence of two well-marked ‘mamelons’ (Fig. 2B–C), but they can be either inconspicuous (cf. Fig. 7B–C in González Molinero & Peña Cantero 2015), marked by simple circular perisarc holes, or completely absent (Fig. 1B). Although only the last state is shown in the figure from the type material (see Fig. 1B), the other conditions (i.e. the presence of two either well-marked or inconspicuous ‘mamelons’) were also observed. See González Molinero & Peña Cantero (2015) for a discussion about the variability in the number and development of the “mamelons” of the cauline apophyses in species of Oswaldella studied using SEM.

Distribution. West Antarctic (Peña Cantero & Vervoort 1998).