Family SCLERODOMIDAE Levinsen, 1909

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Introduction

The family and its type genus were both established by Levinsen (1909), who included Tessaradoma Norman in his original concept. The morphology and taxonomy of the family were reviewed by Gordon (1988), who demonstrated that Cellarinellidae Moyano (1970) could be subsumed within Levinsen's family. As presently constituted the family comprises four genera: Sclerodomus Levinsen, Systenopora Waters (1904), Cellarinella Waters (1904) and Cellarinelloides Moyano. All are limited to the southern hemisphere, and most described species are endemic to Antarctica. Rogick (1956) first revealed the diversity of Antarctic Cellarinella; all Antarctic sclerodomids are described and figured by Hayward (1995).

Sclerodomids develop erect, rigid, thickly calcified bilaminate colonies, anchored to the substratum by chitinous rootlets, or by a spreading sheet of zooid polymorphs. A few grow as slender, irregularly branching, twiglike forms, some develop thick, irregular plates, but the majority form broad-fronded, rather flabellate, colonies. The primary umbonuloid shield is bordered by large areolar pores (frontal septula); this thickens rapidly, ridges between the pores dividing and fusing, and extending centripetally, so that the entire colony surface appears coarsely reticulate, and zooid boundaries are completely obscured. The primary orifice lacks an operculum and is located at the base of a deep peristome. The secondary orifice bears complex folds and grooves, incorporating one or more avicularia; in Cellarinella small avicularia are located within the peristome and may be partly or completely hidden from view. Ovicells are hyperstomial, imperforate, and open into the peristome; they are immersed and hidden by frontal shield calcification in almost all species. Zooid vertical walls are perforated by uniporous or multiporous septula.

Cellarinella comprises 15 species, all but one endemic to Antarctica. Cellarinelloides and Systenopora are presently monotypical for Antarctic endemics. Cellarinella occurs as multispecies communities, in perennial thickets, on medium to coarse substrata on the Antarctic Shelf. Winston (1983) studied the biology and ecology of Ross Sea species. A fossil Cellarinella is recorded from the Pliocene of Antarctica; the Victorian fossil 'Porella' operculata, from the Late Oligocene and Miocene, may belong to the family (Taylor 1993).

Diagnosis

Colony erect, rigid, arising from a sheet of polymorphic zooids, or anchored by rhizoids, thickly calcified, subcircular or flabellate. Zooids in two, to many longitudinal series, facing mainly on one aspect; zooidal boundaries obscured by continuous secondary calcification. Frontal wall regularly porous, the pores in longitudinal sulci where the wall is thicker. Secondary orifice subtriangular to circular, with one or more peristomial avicularia often concealed. Ovicell visible as a bulge in younger zooids, later concealed, opening into the peristome. Uniporous mural septula present

General References

Gordon, D.P. 1988. The bryozoan families Sclerodomidae, Bifaxariidae, and Urceoliporidae and a novel type of frontal wall. New Zealand Journal of Zoology 15: 249-290

Hayward, P.J. 1995. Antarctic cheilostomatous Bryozoa. Oxford, New York, Tokyo : Oxford University Press 355 pp.

Hayward, P.J. 1995. Antarctic cheilostomatous Bryozoa. Oxford, New York, Tokyo : Oxford University Press 355 pp. [213]

Levinsen, G.M.R. 1909. Morphological and systematic studies on the cheilostomatous Bryozoa. Copenhagen : Nationale Forfatteres Forlag 431 pp.

Moyano G., H.I. 1970. Una familia, tres generos y una especie nuevos para la Antartica. Cahiers de Biologie Marine 11: 153-166

Rogick, M.D. 1956. Bryozoa of the United States Navy's 1947-1948 Antarctic Expedition, I-IV. Proceedings of the United States National Museum 105: 221-317

Taylor, P.D. 1993. Bryozoa. pp. 465-489 in Benton, M.J. (ed.). The Fossil Record 2. London & New York : Chapman & Hall 845 pp.

Waters, A.W. 1904. Bryozoa. Résultats du Voyage du S.V. 'Belgica', Zoologie. Expedition Antarctique Belge 4: 1-114

Winston, J.E. 1983. Patterns of growth, reproduction and mortality in Bryozoans from the Ross Sea, Antarctica. Bulletin of Marine Science 33: 688-702

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