Halecium antarcticum Vanhöffen, 1910

Watson, Jeanette E., 2008, Hydroids of the BANZARE expeditions, 1929 – 1931: the family Haleciidae (Hydrozoa, Leptothecata) from the Australian Antarctic Territory, Memoirs of Museum Victoria 65, pp. 165-178 : 166-167

Halecium antarcticum Vanhöffen, 1910

Figure 2A–C

Halecium antarcticum Vanhöffen, 1910: 317 , fig. 34.- Billard, 1914: 7, fig. 5.- Totton, 1930: 144, fig. 4 .- Broch, 1948, 28: 7.- Naumov and Stepanjants, 1958: 57.- Blanco, 1984: 294, figs 8-13, pls. 4-5.

Material examined. NMV F147447, Station 107, two microslides displaying branch fragments and a preserved fertile colony. NMV F147448, Station 107, one microslide displaying branch fragments. NMV F147449, Station 1785, one microslide displaying two small branch fragments .

Description. Fertile colony originally at least 40 mm high. Hydrorhiza reptant on sponge; stolons tubular, rugose, loosely adherent to substrate.

Shorter stems monosiphonic; stems beginning with several broad basal annulations above junction with hydrorhiza; taller stem branched, lightly fascicled with several wide, tangled tubes running almost to tip of colony and along primary branches. Branching irregular and disorderly, branches bent outwards atvarious angles from main stem, ultimatebranches short, straight, monosiphonic. Monosiphonic branch internodes fairly wide, cylindrical, walls smooth, nodes deep, oblique, sloping away from hydrophore, a tumescence and often one or several deep corrugations in perisarc above node.

Primary hydrophores alternate on stem, one distal on each internode, cylindrical, length variable but typically moderately long, abcauline wall curving smoothly away from internode, adcauline wall more or less straight. Hydrotheca bowl-shaped, expanding from diaphragm to margin, rim everted and a little outrolled. Diaphragm fairly distinct, a few desmocytes above.

Hydrophores typically regenerated in linear series of up to five; successive hydrophores variable in length, each arising from diaphragm of preceding hydrotheca; hydrophores with broad basal kinks and up to 10 close corrugations.

Gonothecae probably male, inserted in hydrophore on distal monosiphonic branches; shape variable from flattened clavate to ovoid with a low apical dome with flattened top.

Perisarc of stem, branches and hydrothecae rather thick, very thin on gonothecae.

Colour (preserved material) deep honey brown, paler on monosiphonic branches; gonotheca colourless.

Measurements (μm)

Branch internode length 419 – 514 width at node 176 – 216 Hydrophore length to diaphragm, adcauline wall 196 – 274 Hydrotheca depth, margin to diaphragm 71 – 87 diameter at margin 277 – 316 diameter at diaphragm 174 - 237 Gonotheca length 1,176 – 1,568 maximum width 882 – 910

Remarks. The taller stem is notable for its untidy habit of growth and thickening of the polysiphonic tubes at origin of the primary branches. Several short monosiphonic branches are incipiently anastomosed, two showing reversal of growth so that the hydrophores now face backwards towards the stem.

The gonothecal perisarc is very fragile, few being undamaged, only two showing a flattened apex. As only the spadix and some tissue remains in most gonothecae, sex could not be determined.

As dimensions of the present material fit reasonably well with Vanhöffen’s (1910) and Totton’s (1930) descriptions of Halecium antarcticum , the material is assigned to this species.

Distribution. Halecium antacticum is recorded from depths of 256 m in McMurdo Sound, 290 m in the Ross Sea and 385 m at Gauss Station.

Figures

Figure 2. A - C. Halecium antarcticum from Station 107. A, fertile branch with well defined internodes and mature and developing gonothecae. B, hydrophores and hydrothecae with desmocytes. C, branch with linear regeneration of hydrophores. Scale bar: A, 2 mm; B, 0.3 mm; C, 0.5 mm.

Figure 4. A - C. Halecium brevithecum sp. nov. Holotype. A, branch. B, branch internodes. C, hydrophore and shallow hydrotheca. Scale bar: A, 1 mm, B, 0.5 mm. C, 0.3 mm.