Ellisina antarctica Hastings 1945

"Ellisina antarctica, sр. n. (Fig. 6.)

? Меmbranipora incrustans (part) Waters, 1904, p. 31, p1. ii. fig. 15 a.

? Membranipora incrustans Calvet, 1909, p. 14.

? Membranipora watersi (part) Kluge, 1914, p. 659.

Distribution.—Patagonian Shelf, 96-144 m. ('Discovery' Investigations, Sts. WS 87, WS 243, 1942.5.10.16, 14); Falkland Islands, 75-74 m. ('Discovery' Investigations, St. WS 84, 1942.5.10.10); Heard Island, 274.5 m.

('Challenger,' St. 150, 87.9.2.3) ; South Georgia, 110-342 m. ('Discovery ' Investigations, Sts. 27, 170, WS 33, 1942.5.10. 7,13, 8) ; South Sandwich Islands, 77-152 m. ('Discovery' Investigations, St. 366, 1942.5.10.6 and 1943.8.4.1); South Orkney Islands, 24-36m.('Discovery' Investigations, St. 164, 1942.5.10.11) ; near Elephant Island, 342 m. ('Discovery' Investigations, St. 170, 1942.5.10.12) ; South Shetland Islands, 391 m. ('Discovery' Investigations, St. 195, 1942.5.10.9) ; ? Bellingshausen Sea, 20-30 m. and 485-480 m. (Calvet ; Waters) ; ? Wilhelm II. Land, 385 m. (Kluge) ; Cape Adare, 32.9 m. (National Antarctic Exp., 1942.5.10.5) ; McMurdo Sound, 45.7-54.9 m. (National Antarctic Expedition, No. 12 Hоlе, 1942.5.10.15).

Holotype.—South Sandwich Islands, 1943.8.4.1.

Description.—Zoarium encrusting, rather delicate Zooecia (figs 6) with more or less oval aperture, with very narrow, slightly granular cryptocyst extending along sides and round proximal end of aperture, pore-chambers present, basal wall uncalcified except at its periphery.

Avicularia small, vicarious, placed distally to the zooecia, connected with neighbouring zooecia by pore-chambers, basal wall incompletely calcified. Mandible acutely triangular, directed obliquely.

Ovicells endozooecial, immersed in distal avicularium, closed by zooecial operculum, with small frontal umbo, and, when fully formed, with a pair of smooth and very inconspicuous calcareous tongues curving across front apparently between ectocecium (=wall of avicularium) and entocecium.

Ancestrula almost circular, with circular aperture, an slight proximal gymnocyst. Aperture surrounded by few (about 6 or 7), widely spaced, erect spines.

Remarks.—The cryptocyst in this species is only recognizable as such by analogy with related species. The material from the type-locality consists of numerous colonies on weed t, some of them with their ancestrulæ intact. The first-formed zooecia, like the ancestrula, have widely spaced spines round the aperture. Suссessive zooecia have fewer spines, the great majority having none. The last spines retained are placed one on еach side at a little distance from the distal end of the zooecium. These two spines are sometimes point°

and may appear brown and membranous at the tip or calcareous throughout. Two similarly placed spines are present on one zooecium in a colony from Cape Adare.

The colonies from the Falkland Islands and the Patagonian Shelf have no ovicells, but agree so closely with the Antarctic specimens in their other features that they referred to the same species. Zooecia are sometimes found with a calcareous frontal which may be complete or may leave a small mediаn pore.

The edge of the calcified part of the basal wall can often be seen, in transparent mounts, as a smooth line just within the very slightly crenulated margin of the cryptocyst and at a lower focus.

Synonymy,—The reasons for supposing that Ellisina antarctica may be the Antarctic species referred, by Waters and other authors, to E. incrustons (Waters) are given above (p. 94). E. antarctica differs from E. incrustans in its larger, more prominent avicularia, in its mostly uncаlcified basal wall, in its narrower cryptocyst, in the different sculpture of the ovicell, and in the immersion of the ovicell in an aviсularium. The 'Belgica' material is not represented in the Waters Collection at Manchester and I have not been able to examine any of it.

E. antarctica differs from E. levata Hinks (1882, pp. 249, 467) in the smaller umbo on the ovicell, and in the ovicell being immersed in an aviсularium. It appears, however, that the fenestra distal to the ovicell of E. levata (see Hastings, 1930, p1. viii. fig. 34) is the opesia of a kenozooecium similarly enveloping the ovicell. The two species are thus very closely allied. Spines have not been recorded in E. levata.

In a specimen of Ellisina taken by the British Graham Land Expedition (1942.5.12.1) the zooecia are a little larger than in the typical specimens of E. antarctica, the cryptocyst is a little wider and distinctly granular, and the avicularia enveloping the ovicells are frequently, but not always, directed distally. This may be the form figured by Waters (1904, , p. 31, pl.. ii. fig. 15 b, c) as Membranipora incrustans var grandis. In Waters's figure, however, the distally directed avicularium has a more acutely pointed mandible, and is not related to an ovicell.

A colony of Ellisina from New Zealand ('Terra Novа' Expedition, St. 91, 1945. 5.2.1) agrees with E. antarctica in its zooecia, but has no unbroken ovicell, According to MaсGillivray's figure, E. (Biflustra) sericea (MacGillivray, 1890, p. 107) only differs from E. antarctica in the sculpture on the front of the ovicell which takes the form of a clavate ridge instead of an umbo. Thus, in the absence of a complete ovicell it is not possible to settle whether the New Zealand specimen belongs to E. sericea or E. antarctica. At the margin of the colony from New Zealand there are a number of vicarious avicularia of the same size and shape as those distal to the zooecia, but • without corresponding zooecia.

Waters (1898, p. 687) regarded E. sericea as a synonym of E. levata, but it differs in the sculpture of the ovicell and the presence of an avicularium above the ovicell. All three species appear to be very closely related, but I have not found any intergradation in their characters (cf. key, p. 91), and their distribution, as at present known, is not continuous, E. sericea being found in Australia, E. levata at the Queen Charlotte Islands, and E. antarctica in the Antarctic and sub-Antarctic regions. There is a small specimen from Oran, North Africa (Waters Collection, Manchester Museum), which I examined a good many years ago, and noted as resembling E. antarctica. It is labelled "Membranipora, see dumerilii." " (Hastings, 1945: 94)