Halecium secundum Jäderholm, 1904

Soto, Joan J. & Peña, Álvaro L., 2019, Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica), Zootaxa 4570 (1), pp. 1-78 : 42

Halecium secundum Jäderholm, 1904

( Fig. 14 b–c)

Material examined. ANT XV/3: 48-50, one colony, c. 70 mm high, with male gonothecae; 48-58, one colony, c. 65 mm high; ANT XXI/2: PS65/278, mass of stems, c. 140 mm high, with male gonothecae.

Remarks. The species had not been found with gonothecae since its original description ( Jäderholm 1904), and only male ones are known. Our material is provided with male gonothecae: 1.3–1.5 mm high, 380 µm in maximum diameter; very delicate, easily collapsible; cylindrical, truncated distally; with terminal, circular aperture ( Fig. 14c ). Jäderholm (1904) mentioned a shallow distal furrow and a proximal sharp keel in the gonothecae. However, given the delicate consistency of the gonothecae, we regard Jäderholm’s observations as a probable artefact that occurred when mounting the microslides.

Peña Cantero (2014b) revised the holotype of Halecium brevithecum Watson, 2008 , discussed the few differences between H. secundum and H. brevithecum , and noted that the latter was described from scarce, infertile material mounted in microslides, and that therefore cannot be completely characterized ( Peña Cantero 2014b: 253). According to him, the hydrothecal adcauline wall of H. brevithecum is completely adnate to the internode in the holotype. In the original description, Watson (2008) also indicated that the adcauline hydrothecal wall is adnate to the internode. However, she also pointed out that the adcauline wall of the hydrophore becomes free just below the hydrotheca. This imply that the hydrothecae might also be free. In this sense, a figure provided by her ( Watson 2008: Fig. 4c ) apparently shows a free adcauline hydrothecal wall. It seems, therefore, that this character may vary among hydrothecae, as it has been documented for H. secundum (cf. Peña Cantero 2014b). Peña Cantero (2014b) also indicated that H. brevithecum can be distinguished from H. secundum by the distinctly longer first hydrothecate internode of the branches, the presence of reddish stems, and the perpendicular arrangement of the lower-order branches compared to previous ones. All these features have been clearly observed from the reproductive material of H. secundum . Being so, we consider Halecium brevithecum as a junior synonym of Jäderholm’s species.

Ecology and distribution. Previously reported at depths between 40 (Peña Cantero et al. 2013) and 502 m ( Watson 2008, as H. brevithecum ); present material at 119– 283 m. Circum-Antarctic species (Peña Cantero et al. 2013), with only three validated records and a fourth pending one (see Peña Cantero 2014b), present finding constitutes the first evidence from the Weddell Sea.

Figures

FIGURE 4. a–i Tubularia longstaffi: a polyp-carrying tube; b male polyp; c blastostyle with developing male gonophores; d blastostyle with fully-grown male gonophores; e female polyp; f blastostyle with fully-grown female gonophores; g–h detail of female gonophores carrying actinulae; i actinulae in different stages of development. j–o Zanclea hicksoni: j early-developing polyp, k expanded young polyps, l expanded polyps with hydrorhizal filaments, m contracted polyp, n–o detail of polyps showing tentacle arrangement in linear clusters (arrows).

FIGURE 14. a Halecium incertus: colony. b–c H. secundum: b hydrophore and hydrotheca; c gonothecae. d–g H. tubatum: d stem; e detail of the basal rings of the stem; f–g hydrothecae. h–j Hydrodendron arboreum: h stem showing hydrophores arrangement; i colony; j nematophore.