Acryptolaria frigida Pena Cantero 2014

Acryptolaria frigida Peña Cantero, 2014

(Figs 2B, 3D, 5E, 6A, 7C)

Acryptolaria sp. Peña Cantero et al. 2004: 2281, fig. 2A, B; Peña Cantero 2010: 764, fig. 2e; 2012: 856, fig. 3a.

? Cryptolaria conferta — Hartlaub, 1904: 13, pl. 2 fig. 1.

Acryptolaria frigida Peña Cantero, 2014: 1716–1717, fig. 2c; Soto Àngel & Peña Cantero, 2019: 20, fig. 6a–b.

Material examined. Glacier: 002/002 , two stems, up to 120 mm high, on bryozoans and basibiont of Symplectoscyphus sp.

Description. Stems up to 120 mm high, polysiphonic. Branching alternate, more or less in one plane. Branches up to fourth order. Stems and branches slightly geniculate. Hydrothecae alternate, in one plane. Hydrotheca tubular, cylindrical at free part; diameter only smoothly decreasing basally at adnate part. Hydrotheca strongly curved outwards. Hydrotheca adnate to internode from two thirds to a little less of its adcauline length. Adcauline wall strongly convex. Abcauline wall concave, particularly at distal half. A ring of desmocytes present at hydrothecal base. Hydrothecal aperture circular, directed outwards, roughly parallel to long axis of branch. Rim even, with a few short renovations. A circular closing lid (i.e. an operculum) occasionally present.

Measurements (in µm). Hydrothecae: abcauline wall 1230–1500, free part of adcauline wall 590–960, adnate part of adcauline wall 870–1320, adcauline wall 1610–1940, diameter at aperture 260–280, diameter at base 140. Cnidome: larger microbasic mastigophores, range 18–23 x 6.5–7.5, mean 19.8±1.2 x 7±0.3 (n=10); ratio, range 2.7–3.1, mean 2.8±0.1 (n=10); smaller microbasic mastigophores 8–9 x 3.5–4.

Remarks. A closing apparatus consisting of a circular flap has been observed. This character was already known in the genus for A. operculata (see below).

Acryptolaria frigida has hydrothecae strongly curved outwards. Typically, the adnate part of the adcauline hydrothecal wall is distinctly longer than the free part (one-quarter to one-half free). The hydrotheca is almost completely cyclindrical, the diameter just smoothly decreasing at adnate part, particularly at the most basal part, with a bottle-neck appearance in some hydrothecae.

Ecology and distribution. Acryptolaria frigida is known from depths between 85 (Peña Cantero 2010) and 728 m (Peña Cantero 2014); present material at 412 m. Peña Cantero (2014) found it on gravel and Soto Àngel & Peña Cantero (2019) on sponges and octocorals; here observed epibiotic on bryozoans. Peña Cantero et al. (2004) reported it as basibiont for colonies of Billardia subrufa and Lafoea gaussica; here used as substrate by colonies of Symplectoscyphus sp. Coppiniae in March (Peña Cantero et al. 2004).

Acryptolaria frigida seems to have a circum-Antarctic distribution (Peña Cantero 2014), being known from the Weddell Sea (Peña Cantero et al. 2004; Soto Àngel & Peña Cantero 2019), off Peter I Island (Peña Cantero 2010) and from the Bellingshausen Sea (Peña Cantero 2012), in West Antarctica, and off Queen Mary Coast (Peña Cantero 2014), in East Antarctica. Present material comes from off McDonald Ice Rumples, Caird Coast, Weddell Sea.