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Family STEGINOPORELLIDAE Hincks, 1884


Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Steginoporellidae was introduced by Hincks (1884) (as Steganoporellidae) for the genus Steginoporella Smitt (1873) alone. Later, other genera were included, which are now assigned to the families Onychocellidae and Thalamoporellidae. The genus Steginoporella had a wide distribution extending from the Eocene, which continues today, species occurring in shallow shelf waters to temperate waters throughout the world (Pouyet & David 1979; Cook 1964, 1985).

The first Australian species to be described were assigned to the genus Membranipora, and several were from the Victorian Tertiary deposits (MacGillivray 1895), the names being later given to Recent specimens from northern Australia (Harmer 1900, 1926).

The genus Steginoporella is characterised by large colonies, which may form sheets, or erect, anastomosing plates, more than 0.5 m. wide and high, which are often brightly coloured, red, orange or yellow (Bock 1982; Wass 1984; Cook 1985). Colonies are composed of two types of zooids, both of which possess functional tentacle crowns and viscera. Generally the A-zooids, which are the smaller and more frequent, are regarded as the equivalent of autozooids. The larger, less frequent B-zooids appear to be a specialized kind of avicularium. This view is supported by the occurrence, in only one species, of interzooidal avicularia without tentacles or viscera, in colonies where no B-zooids are present (Banta 1973). All zooids have large membranous frontals, and well-developed cryptocysts which are porous, and descend distally to meet the distal or basal walls, leaving paired opesiular indentations laterally, and forming a polypide tube centrally. The tube may have lateral expansions. The distal part of the opesia is rimmed by an oral shelf, onto which the large operculum fits when closed. The oral shelf is very wide in the B-zooids of some species, to accommodate the large, hooked cuticular teeth which occur on the submarginal sclerite of the operculum. (Harmer 1900, Cook 1964). The opercula are visible with the naked eye (Wass 1984). The tentacle crowns are large and bell-shaped when protruded; the tentacle number ranges from 24 to 28.

Brooding of the single, large embryo takes place in an interior ovisac which occupies the distal half of the zooid. In species where the cryptocyst is inserted high on the distal wall (eg. S. buskii), there is no room for development of the embryo. The calcification of the cryptocyst and polypide tube is progressively resorbed, and the embryo can be seen to occupy the larger part of the zooid when fully developed. The cryptocyst does not appear to recalcify (Cook 1964).

More than a dozen nominal species of Steginoporella have been recorded from Australia. Two of these, S. magnilabris and S. buskii, have a wide distribution in other seas, but others, like S. alveolata, S. haddoni and S. lateralis, are known only from the southwest Pacific. All these species have a northern Australian distribution, from the Northern Territory, Torres Strait or Great Barrier Reef regions (Harmer 1900, Ryland & Hayward 1992). S. truncata and S. tubulosa have a southern range, from Bass Strait and Tasmania. S. truncata, particularly, is widely distributed, and the large colonies 'develop in exposed locations on vertical walls and under overhangs' (Bock 1982). The colonies are probably the largest of local bryozoans, exceeding 0.5 m in diameter, and provide a habitat for a number of other organisms. S. greavesi Livingstone (1926) was reported from near Perth. lt has large, loosely encrusting colonies, and B-zooids are rare or absent.

 

Diagnosis

Colonies erect or encrusting. Zooids subrectangular, with proximal perforate cryptocyst descending at the sides, forming opesiular indentations. Cryptocyst extending centrally to form a polypide tube which may have a terminal expansion. Cuticular operculum reinforced with sclerites closing on a distal oral shelf. Zooids of two types, the 'B-type' being larger, considered analogous to an avicularium. Larval brooding internal; brooding zooids not differentiated.

 

General References

Banta, W.C., 1973. Evolution of avicularia in cheilostome Bryozoa. pp. 295-303 in Boardman, R.S., Cheetham, A.H., & Oliver, W.A. (eds). Animal Colonies. Development and function through time. Stroudsburg : Dowden, Hutchinson & Ross.

Bock, P.E. 1982. Bryozoans (Phylum Bryozoa). pp. 319-394 in Shepherd, S.A. & Thomas, I.M. (eds). Marine Invertebrates of Southern Australia. Handbook of the Flora and Fauna of South Australia Adelaide : Government Printer Part 1 491 pp.

Cook, P.L. 1964. Polyzoa from West Africa. 1. Notes on the Steganoporellidae, Thalamoporellidae, and Onychocellidae. Resultats Scientifiques des Campagnes de la 'Calypso', 41 (Fasc.VI). Annales de l'Institut Océanographique 41: 43-78

Cook, P.L. 1985. Bryozoa from Ghana. A preliminary survey.Bryozoa from Ghana. A preliminary survey. Annales du Musée Royal de l'Afrique Centrale. Série in Octavo. Sciences Zoologiques 238: 1-315

Harmer, S.F. 1900. A revision of the genus Steganoporella. Quarterly Journal of Microscopical Science 43: 225-297

Harmer, S.F. 1926. The Polyzoa of the Siboga Expedition. Part 2. Cheilostomata Anasca. Siboga-Expéditie Report 28B: 183-501

Hincks, T. 1884. Contributions towards a general history of the marine Polyzoa. XIII. Polyzoa from Victoria and Western Australia. Annals and Magazine of Natural History 5 13: 363-369; 14: 276-285

Livingstone, A.A. 1926. Studies on Australian Bryozoa, No. 4. Records of the Australian Museum 15(2): 167-176

Macgillivray, P.H. 1895. A monograph of the Tertiary Polyzoa of Victoria. Transactions of the Royal Society of Victoria ns 4: 1-166

Pouyet, S., & David, L. 1979. Revision systematique du genre Steginoporella Smitt, 1873 (Bryozoa, Cheilostomata). Geobios 12(6): 763-817

Ryland, J.S. & Hayward, P.J. 1992. Bryozoa from Heron Island, Great Barrier Reef. Memoirs of the Queensland Museum 32(1): 223-301

Smitt, F.A. 1873. Floridan Bryozoa collected by Count L.F. de Pourtales, Part 2. Kongliga Svenska Vetenskaps-Academiens Nya Handlingar, Stockholm 11: 1-83

Wass, R.E. 1984. Bryozoans: coloured mats of the sea. pp. 212-213 in Mead & Beckett Publishing (eds). Reader's Digest Book of the Great Barrier Reef. Sydney : Reader's Digest.

 

History of changes

Note that this list may be incomplete for dates prior to September 2013.
Published As part of group Action Date Action Type Compiler(s)
25-Mar-2014 BRYOZOA Ehrenberg, 1831 25-Mar-2014 MODIFIED Dr Robin Wilson (NMV) Elizabeth Greaves (NMV)
12-Feb-2010 (import)