Family PLAGIOECIIDAE Gregory, 1899

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Family PLAGIOECIIDAE Gregory, 1899

Compiler and date details

July 2001 - Dr Philip Bock

Plagioeciidae Canu, F. 1918. Les ovicelles des Bryozoaires cyclostomes. Étude sur quelques familles nouvelles et anciennes. Bulletin de la Société Géologique de France 4 16: 324-335.
Diastoporidae Gregory, J.W. 1899. Catalogue of the fossil Bryozoa in the Department of Geology, British Museum (Natural History). The Cretaceous Bryozoa. London : Trustees of the British Museum 457 pp.

Introduction

The family was introduced by Busk (1859). It presently encompasses a very large number of late Mesozoic, Tertiary and Recent genera and species, many of which are poorly defined. Brood (1972) effectively reviewed European Cretaceous faunas, whereas Harmelin (1976) reviewed Recent Mediterranean genera and species, and discussed the ecology and evolution of generic groups, and made the most useful modern contribution to the taxonomic study of the family. He referred several other families, including the Plagioeciidae and Oncousoeciidae, to the Diastoporidae. The status of these three families remains uncertain. The Oncousoeciidae is considered separately in the current treatment, while the genera assigned in some publications to the Plagioeciidae are included in the Diastoporidae. Walter (1989) reviewed European Jurassic genera, establishing a fossil history for Eurystrotos.

Colonies may be encrusting and unilaminar, or erect, bilaminar and often folded; encrusting colonies are generally lobed. Autozooid tubes are very slender, generally less than 0.1 mm diameter. Gonozooids may be simple, ovoid and positioned between two autozooid tubes, or very extensively lobed, enclosing a considerable number of peristomes. At least ten Recent species have been described from Australia, principally by MacGillivray (1885, 1887), and there is an extensive Tertiary fauna (MacGillivray 1895). Borg (1944) described five new species from Antarctica, all attributed to Diastopora, and including D. reticulata , which resembles Liripora (Hayward & Cook 1983). The generic attribution of these and Australian species of Diastoporidae requires reassessment.

Encrusting diastoporid colonies may develop expansive or narrow lobes, often more or less discoid when juvenile. Erect growths are bilaminar, and often elaborately folded, or may grow as hollow cylinders. The autozooids are in alternating, or sometimes radial, series; boundaries between adnate proximal portions are often indistinct but the distal portion grows as an erect, slender cylinder with a diameter usually less than 0.1 mm. In late ontogeny peristomes may be sealed by calcareous plates. Gonozooids may be small, oval to rectangular, or extensively lobed, spreading between and around peristomes along a large proportion of the colony periphery. The ooeciostome is a short tube, narrower than an autozooid, and not associated with a zooid peristome. Diastopora lineata MacGillivray (1885) was regarded as the type species of Liripora MacGillivray (1887) by Hayward & Cook (1983); however, Taylor & Gordon (2001) demonstrated that the type species is Diastopora fasciculata MacGillivray (1885). L. lineata has large, discoid colonies which add smaller, marginal subcolonies by frontal extension of one or more zooids. It has been reported from South Africa as well as Victoria. Liripora and Plagioecia seem to be closely related; Plagioecia sarniensis was reported from southern Australia by Bock (1982).

The type genus is a Triassic fossil, and perhaps does not occur in Recent seas. Important living genera include Microecia, Plagioecia, Diplosolen, Eurystrotos and Liripora, the last-named originally described from Australia (MacGillivray 1887). L. lineata was described from South African specimens by Hayward & Cook (1983). All southern hemisphere genera and species are in urgent need of taxonomic revision.

Diagnosis

Colony well calcified, discoid when juvenile, encrusting and lobed, or bilaminar, folded or cylindrical. Autozooids very slender, with elongated peristomes. Gonozooids small, oval, or extensively lobed, spreading among autozooid peristomes along the colony periphery. The ooeciostome is short and tubular.