Halecium ralphae Watson and Vervoort, 2000

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 164-165

Halecium ralphae Watson and Vervoort

Figures 14A–D

Halecium beanii .— Ralph, 1958: 332, fig. 10e, pro parte. Halecium sessile . — Hirohito, 1995: 27, fig. 7g, pro parte. Halecium ralphae Watson and Vervoort, 2001: 162 , figs 7a–e.

Material examined. Stn 119, TM K2795, infertile colony on dead solitary coral, specimen alcohol-preserved. Stn 44, NMV F91320, small infertile stem detached from substrate, specimen alcohol-preserved.

Description. Colony 60 mm high and 2 mm thick at base; smaller colony 30 mm high. Hydrorhizal filaments reptant on coral; colony aborescently branched in up to three orders, several branches broken off. Branching occurs from below a hydrotheca, stem and branches heavily fascicled, polysiphonic tubes almost linear to undulating, sometimes knotted around origin of branch, tubes running along branches, ultimate branches monosiphonic. Perisarc of stem and proximal branches thick, thinning out on monosiphonic parts.

Monosiphonic branches (hydrocladia) arising from polysiphonic tubes on an apophysis of stem comprising one to three subspherical segments with strong transverse nodes. Hydrocladial internodes long, cylindrical, smooth, widening distally, nodes slightly oblique, tilted away from hydrotheca, marked by a deep constriction and tumescence in perisarc, sometimes an additional short subspherical internode similar to apophysis above node.

Hydrophores alternate, distal on internode, almost entirely adnate to internode, adcauline wall marked by a seam in perisarc, a semicircular thinning in perisarc below some hydrothecae; abcauline wall contiguous with wall of internode. Hydrotheca free, closely adpressed but not adnate to internode, very shallow, tilted at slightly away from internode, hydrothecal margin very weakly everted, diaphragm distinct, a ring of desmocytes above. Hydranths too poorly preserved for description.

Colour. Stem and fascicled branches honey brown; monosiphonic parts pale brown.

Measurements (µm)

Branch length monosiphonic branch internode 580–800

diameter at node 96–120 Hydrotheca length adnate wall to diaphragm 100–128

diameter at diaphragm 128–144

depth margin to diaphragm 30–38

diameter of margin 152–154

Distribution. Previously recorded from 475–512 m off the Chatham Islands ( Ralph, 1958), shallow water in Japan ( Hirohito, 1995) and from 700–1122 m south of Tasmania ( Watson and Vervoort, 2001).

Remarks. Some large undischarged bean-shaped nematocysts visible in the coenosarc of the branches could not be identified. The marginal rims of some hydrothecae have one or two obscure regenerations. Other than the noticeable thinning of the perisarc of the hydrophore below some hydrothecae the material conforms to the description and dimensions of Halecium ralphae given by Watson and Vervoort (2001).

Figures

Figures 14A–D. Halecium ralphae, stn 119. A, colony. B, distal part of branch. C, apophysis of stem and proximal part of branch. D, hydrophore and hydrotheca. Scale bar: A, 5 mm; B, C, 0.5 mm; D, 0.1 mm.