Halecium sp.

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 167-168

Halecium sp.

Figures 17A–E

Material examined. Stn 122, NMV F91328, fragmentary remaining upper branches of a large fertile colony, specimen alcohol-preserved. Stn 90, TM K2791, specimen alcohol-preserved, NMV F91345, malinol-mounted microslide, from lower stem and denuded branches of very large colony broken off from base.

Description. Stem (or lower branch) from Stn 122, 5 mm wide at base and 150 mm high, rigid, irregularly branched; branches heavily fascicled, tubes running almost to tips of branches. Ultimate branches (hydrocladia) monosiphonic, irregularly alternate, short, hydrocladium issuing from inside a hydrotheca on peripheral tube of stem or polysiphonic tube of branch, perisarc of stem and proximal branches thick, thinner on hydrocladia. Proximal hydrocladial internode with 1 to 4 deep transverse septa, internodes thereafter short, more or less cylindrical, walls smooth to broadly undulated, nodes opposed, tilted away from hydrophore, deeply incised, internode tumid above and below node.

Hydrophores alternate, occupying distal half of internode, abcauline wall sloping smoothly outwards from axis at c. 30°, adcauline wall variable in length, adnate to below hydrotheca, free wall short. Hydrotheca shallow, free of internode, opposite to or just above node, tilted away from internodal axis at c. 110°, expanding slightly to a weakly everted rim; eversion more pronounced on adcauline than abcauline side; in frontal view hydrothecal margin slightly ovoid; diaphragm distinct, transverse to saucer-shaped with central circular hydropore, a circle of inward-facing thorn-shaped desmocytes above diaphragm. Hydranth with c. 16 tentacles, none well preserved.

Gonothecae arising without pedicel on proximal part of internode opposite a hydrophore; a few immature or broken gonothecae present, minute to small, base subspherical, perisarc very thin.

Colour. Colony from Stn 122 honey brown, fading to white on monosiphonic branches. Colony from Stn 90 pale yellowish-green.

Measurements (µm)

Monosiphonic branch length of proximal internode 120–440 length of succeeding internodes 600–820 width at node 160–280

Hydrophore length of adnate adcauline wall 304–416 length of free adcauline wall 56–100

Hydrotheca diameter at diaphragm 232–264 depth margin to diaphragm 48–60 diameter at margin 304–320

Gonotheca width of immature gonotheca 120

Remarks. The heavily fascicled branches are woody and very brittle. There is little tendency to secondary branching and there are few regenerated hydrophores in the colonies. Although most hydrophores are oppositely arranged on the hydrocladium, there is a tendency to frontal displacement on some branches.

The few small gonothecae present were noted only during detailed examination of the material. They may be female, but the very thin perisarc is so collapsed and torn that the shape of the mature gonotheca could not be reconstructed or the sex determined. Species with strongly fascicled colonies considered were the near-cosmopolitan Halecium beanii ( Johnston, 1838) , H. luteum Watson, 1975 from Tasmania and H. jaederholmi Vervoort, 1972b , known from Antarctic and subantarctic waters. However, structure and dimensions of the hydrotheca and shape of the internode of these species all differ from the present specimen. As the material is fragmentary it is not to assigned to species.

Figures

Figures 17A–E. Halecium spec., stn 90. A, colony. B, polysiphonic stem with monosiphonic branches. C, monosiphonic branch with hydrophores. D, young gonotheca erupting from stem. E, more advanced gonotheca, distal end damaged. Scale bar: A, 50 mm; B, 1 mm; C, 0.2 mm; D, E, 0.1 mm.