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Classification


Antarcticaetos   Genus

Synonymy

Original Description
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"Antarcticaetos gen. nov.

Diagnosis

Colony erect, slender, branching dichotomously, with or without tubular, chiti­nous nodes at the base of each ramus ; cylindrical, with autozooids opening around the whole circumference of the branch. Autozooids with umbonuloid frontal wall development, and well marked marginal frontal septula. Proximal edge of aperture produced as a pronounced lip, but lacking denticles ; no distal oral spines. Avicu­laria adventitious, sporadic ; developed on one or both sides of the aperture, in the axil of the aperture lip, small ; a gigantic adventitious avicularium, with elongate, hooked rostrum, sporadically developed on frontal surface, close to aperture lip. Ovicell developed from distal wall of autozooid, recumbent on succeeding auto-zooid, smooth, imperforate.

Type species : Escharoides bubeccata Rogick, 1956.

Discussion

E. bubeccata (Fig. 1D-F) was described by Rogick (1956) in her account of the Antarctic species of Escharoides Milne Edwards, to which it certainly bears a su­perficial resemblance. However, E. bubeccata differs from all species of that genus not only in its delicate, erect colony form, but also in certain other features of its morphology. In Escharoides the strongly calcified autozooids are linked by well developed basal pore chambers, while in E. bubeccata interzooidal communication is through small, multiporous septula. Its delicate apertural lip is quite unlike those of other species, which have a complex series of denticles and internal ridges, and it lacks the distal oral shelf and well developed spines characteristic of Escharoides. E. bubeccata is clearly adapted for a different mode of living than those of the encrusting species of Escharoides, nonetheless, its morphology is sufficiently distinct to warrant the introduction of a new genus.

Several of the "Discovery" samples comprised large numbers of colonies, inclu­ding flat-sectioned rods, slender, nodulated growths, and branching colonies with one or two bifurcations. The colonies were mostly about 20 mm high, rarely attai­ning 30 mm ; the most slender comprised rods with whorls of three autozooids, while the broad flat colonies had a maximum of eight whorls. In some instances autozooid rows were continuous above and below dichotomies ; in others a node consisting of a bundle of chitinous tubes was interposed above the dichotomy. These arose from short, tubular units lacking apertures, and developed distally as normal autozooids. The nodes perhaps coincide with periodic growth checks.

Geographical distribution

Rogick's material of A. bubeccata was collected from two stations in the Ross Sea. The present material comprised 16 samples from McMurdo Sound, Ross Sea, from the collections of the National Antarctic Expedition ; the British Antarctic Expedition yielded two further samples, "Terra Nova" stns. 339 and 340, also from the Ross Sea. The "Discovery" collections included seven samples of A. bubeccata, four from the Ross Sea ("Discovery" stns. 1644, 1651, 1652, 1660), but also from Signy Island, South Orkney Islands (stn 167, 60° 50.5' S, 46° 15' W, 244 - 344 m), from the Bismarck Strait, Palmer Archipelago (stn 190, 64° 56' S, 65° 35' W, 315 m) and from the South Sandwich Islands (stn. 371, 1 mile east of Montagu Id., 99 -161 m). A. bubeccata is likely to have a circumpolar distribution and is certainly an

endemic Antarctic species." (Hayward and Thorpe, 1988:280-1)

Geographic Distribution

Ross Sea, Signy Island, South Orkney Islands, Bismarck Strait, Palmer Archipelago, South Sandwich Islands

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