Halecium exaggeratum Peña Cantero, Boero & Piraino, 2013

ÁLVARO L. PEÑA CANTERO, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa, Zootaxa 4293 (1), pp. 1-65 : 48-50

Halecium exaggeratum Peña Cantero, Boero & Piraino, 2013

( Figs 15 C–E, 16A–B)

Halecium exaggeratum Peña Cantero et al., 2013: 743 , fig. 6d, e; Peña Cantero, 2014b: 255 –256, fig. 5K (synonymy).

Material examined. Stn 67, polysiphonic stem 60 mm high on bryozoan, with male gonothecae, basibiont of Hebella plana (NIWA 117593).

Description. Stem 60 mm high, strongly polysiphonic, irregularly branched. Some primary branches also polysiphonic, very long, becoming second-order stems. Secondary stems give rise to other branches, some also distinctly polysiphonic, becoming lower-order stems. Branching up to five-order. Stem and branches divided into internodes by alternately arranged oblique nodes. Internodes slightly arranged in zigzag. Branches typically originating from hydrophores ( Fig. 15 C); usually as single branches, although few paired branches, arising from opposite sides of hydrophore, also present. Some branches originating from hydrothecae.

Hydrophores long, free, with distal hydrotheca ( Figs 15 C–D, 16A); ratio adcauline length of hydrophore:diameter at diaphragm 1.3–2.5. Hydrophores straight, regularly diverging from internode. Hydrothecae extensively surpassing distal node of internode ( Figs 15 C–D).

Hydrotheca low, widening distally, more adcaudally. Rim markedly everted ( Figs 15 C–D, 16A). No pseudodiaphragm. Usually single secondary hydrotheca at end of relatively long pedicel, sometimes with several basal rings.

Gonothecae flattened, triangular, strongly narrowing at base ( Figs 15 E, 16B).

Measurements (in µm). Hydrothecae: diameter at aperture 150–170, diameter at diaphragm 100–115, height 40–50. Hydrophore: adcauline length 140–270. Gonothecae: height 730–840, maximum diameter 650–700. Cnidome: microbasic euryteles (7.5– 8 x 4–4.5) and microbasic mastigophores (6.5– 7 x 2 µm).

Remarks. The present material differs from the concept of this species in being polysiphonic (cf. Peña Cantero 2014b). However, the polysiphonic/monosiphonic condition could be related to the degree of colonial development. Only stems up to 15 mm high had been reported, whereas the present material reaches 60 mm in height. The studied material also differs in having a slightly lower ratio between adcauline length of hydrophore and diameter at diaphragm than in the original description (2.5–3.3 see Peña Cantero et al. 2013), although similar to that of other material brought to this species by Peña Cantero (2014b). The diameter at the hydrothecal aperture is also slightly smaller than in the original description (200–215 µm, see Peña Cantero et al. 2013). However, the present material perfectly agrees in the remaining trophosome characteristics and even in the shape and size of the gonothecae described by Blanco (1984: pl. 5 fig. 13). It also shares the type and size of nematocysts.

Ecology and distribution. Recently reviewed by Peña Cantero et al. (2013) and Peña Cantero (2014b). Shelf species (Peña Cantero et al. 2013), found at depths between 25 (Peña Cantero et al. 2013) and 350 m ( Hartlaub 1904); present material between 272 and 286 m, epibiotic on a bryozoan and basibiont of H. plana , and with gonothecae in February.

Circum-Antarctic distribution (Peña Cantero et al. 2013). In the Ross Sea, already known from Tethys Bay (Peña Cantero et al. 2013). Present material collected off Cape Hallet.

Figures

FIGURE 15. Halecium banzare Watson, 2008: A, internodes with primary and second-order hydrothecae; B, gonotheca. Halecium exaggeratum Peña Cantero, Boero & Piraino, 2013: C, internode with primary and secondary hydrotheca as well as lower-order branch; D, internodes with primary hydrothecae; E, gonotheca. Halecium interpolatum Ritchie, 1907: F, internode with primary hydrotheca and internode structure. Halecium jaederholmi Vervoort, 1972: G, internodes with primary hydrothecae. Halecium secundum Jäderholm, 1904: H, internode with primary hydrotheca. (A from Stn 53; B from Stn 139; C – E, H from Stn 67; F from Stn 107; G from Stn 112). Scale bar: 250 µm.