Halecium elegantulum Watson 2008

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).