Halecium elegantulum Watson, 2008

Peña Cantero, Álvaro L., 2014, Revision of the Antarctic species of Halecium Oken, 1815 (Cnidaria, Hydrozoa, Haleciidae), Zootaxa 3790 (2), pp. 243-280 : 253-255

Halecium elegantulum Watson, 2008

( Fig. 5 A–F)

Halecium elegantulum Watson, 2008: 170 –171, fig. 6A–C.

Material examined. Holotype, BANZARE , Stn 103, 67°03'S – 74°29'E (Mawson Coast), 437 m, 10.2.31, two microslides (Hydr. 709/13, F147463.1 & F147463.2), several stems on Symplectoscyphus cf. glacialis , together with Filellum sp. and Opercularella sp.

Diagnosis. Tiny, monosiphonic, unbranched stems, formed by a series of hydrothecae, each emerging from previous one far below its rim. Hydrotheca strongly widening distally; rim slightly everted. Neither diaphragm nor desmocytes present. Cnidome and gonothecae unknown.

Description. Stolonal hydrorhiza. Pedicels extremely long, up to several millimetres high ( Fig. 5 A, B). Stems unbranched ( Fig. 5 A–C), but formed by a series of hydrothecae, each emerging from the previous hydrotheca ( Fig. 5 C). Sometimes, pedicels provided with a single distal hydrotheca ( Fig. 5 B).

Hydrothecae strongly widening distally ( Fig. 5 A–F), rim slightly everted ( Fig. 5 D, F). Apparently, neither diaphragm nor desmocytes present ( Fig. 5 D–F). Lower-order hydrothecae arising far below rim of previous hydrotheca, not from diaphragm as usually happens to species of Halecium .

Gonothecae absent.

No nematocysts could be observed.

Measurements (in µm). Hydrothecae: diameter at aperture 110–130, diameter at origin of lower-order pedicel 60–70, height from origin of lower-order pedicel to hydrothecal rim 25–50. Internodes: length several millimetres, diameter 50–55.

Remarks. This species is peculiar and easily recognizable by the colony structure with unbranched, delicate stems, consisting of a succession of lower-order hydrothecae, as well as by the absence of hydrothecal diaphragm.

Ecology and distribution. Halecium elegantulum is only known from off Mawson Coast, where it was found at a depth of 437 m ( Watson 2008).

Figures

FIGURE 5. Halecium elegantulum Watson, 2008. (A – B) complete stems; (C) fragment of stem showing hydrothecal arrangement; (E – F) detail of hydrothecae. Halecium interpolatum Ritchie, 1907. (G) fragment of stem showing branching and internode structure; (H, J) part of stems showing hydrotheca and internode structure; (I) incipient stem. Halecium tenellum (sensu Hartlaub, 1904). (K) fragment of stem showing internode structure and primary and second-order hydrothecae. Halecium tubatum Watson, 2008. (L) incipient stem. (A – G, L from type material; H – J from material originally described as H. tubatum). Scale bar: 125 µm (D – F), 250 µm (C, G – L), 500 µm (A – B).