Staurotheca polarsterni Pena Cantero, Svoboda & Vervoort 1997

Staurotheca polarsterni Peña Cantero, Svoboda & Vervoort, 1997

(Fig. 11 C–E)

Staurotheca polarsterni — Peña Cantero et al., 1997a: 365 –368, figs 9, 13D; Peña Cantero & Vervoort, 2003: 2702 –2703; Peña Cantero, 2008: 460; 2014a: 1723, fig. 5f–i.

Material examined. Stn 18, stem fragment 115 mm long, in bad condition, with female gonothecae (NIWA 117544); Stn 19, distal stem fragment 70 mm long (MNCN 2.03/616).

Description. Stem fragments up to 115 mm long. Branching alternate in more or less one plane. Up to fourth order branches present. Branches distinctly curving upwards, sinuous, and with frequent perisarc constrictions followed by a distinct reduction in branch diameter, which is recovered later. Branch diameter usually smaller than that of stem.

Hydrothecae arranged in decussate verticils of three to six, resulting in six to 12 longitudinal rows of hydrothecae. Distal part of hydrotheca directed outward, distinctly protruding; adcauline wall almost completely adnate. In frontal view, hydrotheca usually gradually widening toward its base. Hydrotheca without mushroomshaped diaphragm (Fig. 11 C–E).

Measurements (in µm). Cnidome: larger microbasic mastigophores [range 21.0–22.0 x 4.5–5.0, mean 21.5±0.4 x 4.8±0.3 (n=10); ratio, range 4.2–4.9, mean 4.5±0.3 (n=10)].

Remarks. There are some branches originating from within gonothecae. There is even one case in which one branch originates from within a gonotheca and another branch from the lateral wall of the same gonotheca.

It is difficult to distinguish this species from S. pachyclada when only scarce, fragmentary material is available, which makes it impossible to know the colony structure, because hydrothecae may be similar in both species. However, they can be identified because S. polarsterni might be characterized both by the uneven diameter of stems and branches, with frequent reductions and increases, contrary to what happens in S. pachyclada where the diameter is more or less constant, and by the outline of stem and branches, which is distinctly sinuous, whereas it is straight in S. pachyclada.

Ecology and distribution. Shelf and slope species, found at depths from 181 to 1030 m (Peña Cantero et al. 1997a); present material between 429 and 530 m, with gonothecae in February. Gonothecae previously reported in October, December and February (Peña Cantero et al. 1997a).

Circum-Antarctic distribution (Peña Cantero et al. 1997a), known from the Davis Sea (Stepanjants 1979), the Weddell Sea (Peña Cantero et al. 1997a) and off Deception Island (Peña Cantero 2008). Present material is the first record from the Ross Sea, off Possession Islands.