Orthopyxis norvegiae ( Broch, 1948 )

Galea, Horia R. & Schories, Dirk, 2012, Some hydrozoans (Cnidaria) from King George Island, Antarctica, Zootaxa 3321, pp. 1-21 : 16-17

Orthopyxis norvegiae ( Broch, 1948)

(Pl. 1T, Fig. 3R–T, Z2)

Campanularia (Orthopyxis) norvegiae Broch, 1948: 16 , fig. 5.

Orthopyxis norvegiae — Branch & Williams, 1993: 9, fig.

Campanularia norvegiae — Millard, 1977: 18, figs 5A–E. —Peña Cantero, 2006 (pro parte): 944, fig. 5B, C (not fig. 5D =? Campanularia sp.).

not Campanularia norvegiae — Stepanjants, 1979: 30, pl. 5, figs 2A, B (= Campanularia sp.).

Material examined. Stn. PNS — 07.ii.2011, Ant.13/2011 (10 m): fertile female colony on seaweed (MHNG- INVE-79780). Stn. RAS — 21.ii.2011, Ant.12/2011 (15–20 m): small colony composed of several hydrothecae and immature gonothecae, epizoic on Sertularella gaudichaudi ; Ant.14/2011 (20–30 m): male and female colonies on seaweed (MHNG-INVE-79663).

Description. Colonies arising from creeping, branching, anastomozing hydrorhiza. Pedicels 1.0– 4.5 mm high, 85–95 µm wide, distinctly spirally twisted throughout, occasionally spiral furrow less distinct. Hydrotheca deep (585–820 µm), campanulate, rounded to slightly ovoid in transverse section, 365–440 µm wide, with much thickened perisarc, especially basally where it forms a prominent diaphragm delimiting an ovoid subhydrothecal chamber, as well as just below the aperture; rim prolonged by a thinner perisarc sheet (50–80 µm high), margin even, slightly everted; aperture diameter 330–460 µm. Between hydrotheca and pedicel, a subhydrothecal spherule. Colonies dioecious. Gonothecae borne on distinct, spirally ringed pedicels; bottle shaped to fusiform, perisarc conspicuously thickened; aperture distal, circular; female 2070–2275 µm long, 690–815 µm wide, pedicel 195–275 µm long; male 1380–1920 µm long, 495–715 µm wide, pedicel 275–330 µm long. Gonophores, medusoids with four radial canals and perradiar gonads, with no mouth; sense organs (statocysts) could not be observed in fixed material. Nematocysts: possibly microbasic mastigophores (though none was observed discharged) in two size classes, with large (13.1–14.4) × (3.4–3.7) µm and small (6.0–6.3) × (1.8–2.0) µm capsules.

Remarks. Millard (1977) found planulae in the female gonothecae of her material and concluded that this species does not produce medusoids. However, our observations falsify this assertion. Unlike the females, morphology of male medusoids is more easily understood in the available fixed material, due to their more homogenous tissues and differences in color between the gonads (whitish) and the four radial canals (comparatively darker). Internal structure is clearly seen in transverse sections, even in unstained material (Fig. 3T).

It is not surprising to note that embryonic development takes places within the female gonotheca. A similar situation was equally observed in both Campanularia sp. and Silicularia pedunculata ( Jäderholm, 1904) , possibly as a survival strategy when facing severe environmental conditions.

The gonothecae described and figured by Peña Cantero (2006) possibly do not belong to the present species, and recall instead those of Campanularia sp. In our material, both species often co-occur on the same substrates and their luxuriant colonies are generally well individualized, though in some cases they could be mixed, as illustrated in sample Ant.14/2011.

Geographical distribution. South Georgia ( Broch 1948), Kerguelen Shelf ( Millard 1977), Marion and Prince Edward islands ( Branch & Williams 1993), South Shetland islands (Peña Cantero 2006, present study).