Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island Author Watson, Jeanette W. text Memoirs of Museum Victoria 2003 2003-12-31 60 2 151 180 https://museumsvictoria.com.au/collections-research/journals/memoirs-of-museum-victoria/volume-60-issue-2-2003/pages-151-180/ journal article 10.24199/j.mmv.2003.60.18 1447-2554 12207807 Halecium ovatum Totton Fig. 15D, E Halecium ovatum Totton, 1930: 143 , fig. 3.— Vervoort, 1972b: 339 , fig. 1.— Stepanjants, 1979: 103 , pl. 20 figs 1a–g.— Peña Cantero, 1991: 48 , pl. 2 figs g, h.—Blanco, 1994: 156.— Peña Cantero and García Carrascosa, 1995: 12 , figs 2G, H.— Peña Cantero and García Carrascosa, 1999: 212 . Material examined. Stn 120, TM K2780, NMV F91321, sparse infertile colonies on Halecium ralphae , specimen alcohol-preserved. Description. Colony minute, stolonal; stolons tubular, walls crumpled, thin. Primary hydrophore seated on a short apophysis of the stolon, a transverse to weakly oblique node at base; hydrophore relatively long, cylindrical, smooth, gradually expanding to hydrotheca. Secondary and tertiary hydrophores arising in a series without basal node from diaphragm of preceding hydrotheca; successive hydrophores progressively shorter. Branching of hydrophore at right angles from below a hydrotheca common, secondary hydrophores shorter, with 2 or 3 partial basal constrictions. Hydrotheca shallow, expanding smoothly from well marked diaphragm to wide margin with strongly recurved and outrolled rim, a clear ring of desmocytes above diaphragm. Perisarc of hydrorhiza very thin, that of hydrophores thicker, rim of hydrotheca thin. Colour. Colourless. Measurements (µm) Hydrorhiza width of stolon 80–104 Hydrophore length of primary, proximal node to diaphragm 120–496 width, primary proximal node 59–62 length of succeeding hydrophores 142–316 diameter at diaphragm 120–136 depth, margin to diaphragm 32–44 diameter, marginal rim 176–208 Distribution. Antarctic ( Stepanjants, 1979 ; Peña Cantero and García Carrascosa, 1999 ). Remarks. The species is similar to Halecium tenellum for which it was originally mistaken in samples from Stn. 120. In size and habit of colony the present specimens most resemble Halecium ovatum Totton, 1930 redescribed and figured by Vervoort (1972b) . Although the hydrotheca is narrower and shallower than that of H. ovatum , in the absence of gonosome the material is assigned to that species. The stolons of H. tenellum and H. ovatum entwine on the same substrate and although difficult to differentiate, the two species can be distinguished by the strictly stolonal habit of H. ovatum , its broader, undulating and thinner-walled hydrorhizal stolons, branching of the subsidiary hydrophores from below the primary hydrophore, the greater overall cauline dimensions, the less strongly flared and outrolled rim and the ratio of diameter of hydrothecal rim to width of diaphragm (in H. ovatum 1.5:1, in H. tenellum 2:1).