Family DIDYMOSELLIDAE Brown, 1952

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Family DIDYMOSELLIDAE Brown, 1952

Compiler and date details

July 2001 - Dr Philip Bock

Didymosellidae Brown, 1952.

Introduction

The Family Didymosellidae was introduced by Brown (1952) for Didymosella, erected by Canu & Bassler (1917) and Tubiporella, erected by Levinsen (1909). The type species of both genera had first been described from Victoria, by MacGillivray; D. larvalis in 1869 and T. magnirostris in 1883.
The colonies are loosely encrusting, semi-repent or erect, arising from an encrusting base. The ancestrula of D.larvalis has a complex spinous frontal shield (Cook & Chimonides 1981). The autozooids have a partially calcified basal wall (in D. larvalis) or septular pores leading to a colony-wide basal coelom, with extrazooidal calcification. The cryptocystidean frontal shield has an extensive hypostegal coelom loosely covered by a thick cuticle. The autozooids have prominent, marginal frontal septular pores and some other frontal pores. The calcification becomes very thickened and irregular with ontogeny, obscuring zooid boundaries. The primary calcified orifice is not well-defined, the operculum forming a flap at the distal end of the ascus wall. Peristomes are very long, and prominent early in ontogeny, later becoming immersed, with paired foramina frontally. Alternatively, the frontal shield may have a spiramen opening just proximally to the operculum. Avicularia are adventitious and usually unilateral, arising from frontal septulae, with a large subrostral chamber with marginal pores. The rostrum is orientated laterally, and is acute, sometimes channelled terminally for reception of the elongated mandible which is hinged on a bar, and usually hooked and may be expanded and fringed laterally. Brooding zooids are dimorphic, but the difference is barely detectable in the shape of the peristome: the brood chamber is a distal expansion of the peristome, above the operculum.
The family includes two major generic groups. The type species of Didymosella, D. larvalis, often encrusts algae or seagrass (Bock 1982), and occurs from Western Australia, South Australia, Victoria, Tasmania and New South Wales. Other Recent species occur from Brazil, Cuba, and the Philippines. The genus has a long fossil history extending from the Middle Eocene of France and the Upper Eocene of Spain and Florida. Species are also known from the Oligocene of New Zealand and the Miocene of Victoria. Tubiporella magnirostris occurs from Victoria, Tasmania, southern Western Australia, and the Amirante Islands, and is also known from the Victorian Tertiary. Other species are known in the southwestern Pacific (Cook & Chimonides 1981).