Family EURYSTOMELLIDAE Levinsen, 1909

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Family EURYSTOMELLIDAE Levinsen, 1909

Compiler and date details

July 2001 - Dr Philip Bock

Australianidae Powell, N.A. 1966. Studies on Polyzoa (Bryozoa) from the "Endeavour" Expedition, 1909-1914, pts. 1 and 2. Records of the Australian Museum 27(2): 17-32 [19].
Eurystomellidae Levinsen, G.M.R. 1909. Morphological and systematic studies on the cheilostomatous Bryozoa. Copenhagen : Nationale Forfatteres Forlag 431 pp. [314].

Introduction

Levinsen (1909) introduced the family Eurystomellidae to accomodate his genus Eurystomella, and its type species, Lepralia foraminigera Hincks (1883) from New Zealand. He also included L. bilabiata Hincks (1884), from the northern Pacific. Gordon (1984) noted that in E. foraminigera and E. crystallina from New Zealand, the gymnocystal frontal shield showed vestiges of costae proximal to the orifice. He therefore assigned the genus to the Catenicelloidea. Powell (1966) introduced the family Australianidae for colonies of an unusual, rooted, lunulitiform species from New South Wales, which he called Australiana bifenestrata. Cook & Chimonides (1981) later reviewed Eurystomella and included Australiana as a junior synonym of the genus Selenariopsis Maplestone (1913).

The Eurystomellidae is characterised by the extensive, smooth, usually imperforate, gymnocystidean frontal calcified shield of the autozooids, and the large orifices, which have paired lateral embayments of cryptocyst associated with the insertion of the opercular muscles and sometimes vestigial proximal costae. E. foraminigera also has large, cuticle-covered windows in the frontal shield, which have a rim of cryptocyst, but these do not occur in other species or genera. A range of communication pores, from pore-chambers to septulae occurs among the various species. Avicularia and oral spines are absent. The ovicells are endozooidal and are closed by the operculum. The brood chamber is frequently surrounded by a distal kenozooid with one or more frontal windows, with a marginal cryptocyst and cuticular frontal wall. Colonies of Eurystomella are encrusting, biserial or multiserial.

The only Australian genus of Eurystomellidae, Selenariopsis, has one Recent species, S. gabrieli, which has small, delicate, lunulitiform colonies anchored by large basal rhizoids. The autozooid orifice is elongated, with a proximal sinus and minute lateral embayments. The ovicell and its distal kenozooid are large, with paired frontal windows (Cook & Chimonides 1981). S. gabrieli occurs in 'typical' sand faunas from depths of 60 to 1000 m., from the New South Wales, Victorian and Western Australian coasts. Other species of Selenariopsis are present in the Miocene deposits of Victoria (Bock & Cook, 1996).

Diagnosis

Colony thinly calcified, forming encrusting sheets, or free-living, lunulitiform, anchored by basal rhizoids. Zooids with extensive gymnocystal frontal, with minute oral cryptocyst embayments and small, proximal costal areas. Avicularia absent. Ovicells large, immersed, sometimes kenozooidal, with uncalcified frontal windows.