Halecium tenellum Hincks, 1861

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 165-166

Halecium tenellum Hincks

Figures 15A–C

Halecium tenellum Hincks, 1861: 252 , pl. 6 figs 1–4.— Hartlaub, 1904: 13, pl. 1 fig. 5.— Hartlaub, 1905: 609, fig. 63.— Jäderholm, 1905: 13, pl. 4 fig. 8.— Hickson and Gravely, 1907: 28.— Ritchie, 1907: 525, pl. 2 fig. 4.— Vanhöffen, 1910: 320, fig. 36.— Hilgendorf, 1911: 540.— Linko, 1911: 26, 240, fig. 5.— Ritchie, 1913: 10, 14.— Broch, 1918: 46, fig. 20.— Jäderholm, 1919: 5, pl. 1 fig. 3.— Stechow, 1919: 41, figs J–K.— Stechow 1923a: 5.— Hargitt, 1927: 507.— Broch, 1927: 115.— Broch, 1928: 61.— Broch, 1933: 17.— Fraser, 1937: 110, pl. 23, fig. 121.— Leloup, 1937: 4, 17, fig. 8.— Fraser 1938: 133.— Fraser, 1939: 159.— Fraser, 1948: 225.— Dawydoff, 1952: 54.— Hamond, 1957: 307, fig. 14.— Millard, 1957: 193, fig. 5.— Vervoort, 1959: 229, fig. 8.— Yamada, 1959: 31.— Leloup, 1960: 220, 230.— Naumov, 1960: 454, fig. 344.— Mammen, 1965: 9, fig. 35.— Vasseur, 1965: 52, 70.— Millard, 1966: 471, figs 11C–F.— Vervoort, 1966: 102, fig. 2.— Millard, 1968: 253, 258.— Vervoort, 1968: 95.— Day et al., 1970: 12.— Hirohito, 1974: 8, fig. 2.— Leloup, 1974: 11.— Millard and Bouillon, 1974: 5, fig. 22.— Rho and Chang, 1974: 136, pl. 1 figs 1–4.— Vasseur, 1974: 158.— Cornelius, 1975: 409, fig. 12.— Millard, 1975: 156, figs 50F–L.— Millard, 1977a: 11.— Millard, 1977b: 106.— Rho, 1977: 252, 414, pl. 71 fig. 63.— Millard, 1978: 193.— Stepanjants, 1979: 104, pl. 20 figs 5A–V.— Millard 1980: 130.— Hirohito 1983: 5, fig. 11.— Stepanjants 1985: 137.— Antsulevich 1987: 106. - Gili, Vervoort, and Pagès, 1989: 81, fig. 10A.— Cornelius and Ryland, 1990: 140, fig. 4.— Calder, 1991: 22, fig. 14.— El Beshbeeshy, 1991: 40, fig. 6.— Ramil and Vervoort, 1992: 90, figs 21f, g.— Medel and Vervoort, 2000: 23.– Schuchert, 2001: 85, figs 70A–E.

Halecium (?) tenellum . — Ralph, 1958: 340, figs 11f, g.

Halecium geniculatum Nutting, 1899: 744 , pl. 63 figs 1a–d (not Halecium geniculatum Norman, 1867 (= Halecium halecinum ( Linnaeus, 1758)) .

For full synonymy see Cornelius (1975).

Material examined. Stn 120, TM K2779, infertile colony of many stems on stem of Eudendrium?cyathiferum , specimen alcohol-preserved.

Description. Hydrorhiza tubular, undulating, reptant on hydroid host. Stems to 5 mm high, straggling, given off irregularly from hydrorhiza; stems monosiphonic, beginning with two or three deep transverse annulations, branching thereafter mostly alternate in one plane, straight to sympodial or irregularly dichotomous; stem internodes long, thin, cylindrical, variable in length, perisarc smooth, nodes oblique to transverse, marked by one to three distinct constrictions in perisarc.

Primary hydrophore given off below node, cylindrical, base contiguous with or inclined outwards from internode, variable in length but usually fairly short, hydrotheca moderately deep, diaphragm distinct, transverse, a slight thickening of hydrothecal wall around diaphragm, a faint ring of desmocytes above; margin wide, strongly everted with recurved rim. Hydrophores regenerated linearly up to 10 times, each arising from diaphragm of preceding one, regenerations similar to primaries but length highly variable; base contracted into diaphragm of preceding hydrotheca. Perisarc of hydrorhiza and proximal stem thinning distally, hydrothecal rim very thin.

Colour. White to colourless.

Measurements µm

Hydrorhiza diameter 68–80 Stem internode length of proximal internode 1200–1600

length of succeeding internodes 440–1320

diameter at node 60–80 Hydrophore adcauline length of primary hydrophore 136–232

length of succeeding hydrophores 68–260

diameter of hydrotheca at diaphragm 78–80

depth, margin to diaphragm 24–36

diameter of marginal rim 130–150 Distribution. Near-cosmopolitan in Atlantic, Indian and Pacific Oceans (if all previous identifications of the species are correct). Depth range, 0–550 m ( Millard, 1975). The present record (1046 m) is the deepest for the species.

Remarks. The species is small and elegant. The diameter of the widely flared and outrolled, thin hydrothecal rim is twice that of the diaphragm. The desmocytes above the diaphragm are very faint and visible only under high magnification. Some stems have apical tendrils which revert to stolons.

Although the colonies are not strictly fascicled a few stems have one or two extra tubes that become free above the base as independent monosiphonic branches. Because of its small size and epizoic habit H. tenellum is easily overlooked and can be identified with certainty only when fertile. The present specimens conform reasonably well with descriptions and dimensions (where given by authors) of H. tenellum .

Figures

Figures 15A–E. A–C, Halecium tenellum, stn 120. A, single stem from colony. B, linear series of hydrophores. C, hydrophores and hydrothecae with outrolled rims. D–E. Halecium ovatum, stn 120. D, linear series of hydrophores. E, secondary hydrophore given off below primary. Scale bar: A, 1 mm; B, 0.25 mm; C, 0.1 mm; D, E, 0.5 mm.