Family HELIODOMIDAE Vigneaux, 1949

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Family HELIODOMIDAE Vigneaux, 1949

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Heliodomidae was introduced by Vigneaux (1949) and the name is a senior synonym of Setosellinidae, which was later introduced by Hayward & Cook (1979) for the free-living genera Setosellina and Heliodoma. Colonies typically encrust very small substrata, becoming free peripherally. Each autozooid has an interzooidal avicularium distally or disto-laterally, with a long, setiform mandible. Ovicells are large and closed by the operculum.

Colonies of Setosellina are budded in disto-lateral series early in ontogeny, and differ from those of Heliodoma, which are formed from a pair of laterally budded, interdigitating spiral series (Harmelin 1977). Setosellina has zooids with a narrow cryptocyst, and is a frequent member of any warm-water 'sand fauna'. Specimens of an unnamed species of Setosellina have been found in samples of bottom sediment from Western Australia, but have not been described. The genus is almost certainly present in other Australian waters, but not recorded, as the colonies are very small.

The genus Cranosina was introduced by Canu & Bassler (1933) for Membranipora coronata, which Hincks (1881) first described from 'Singapore or the Philippines'. Cranosina has often been referred to the Hincksinidae (Fransen 1986, Chimonides & Cook 1994), but this family is inappropriate because the type species of Hincksina is referable to the family Flustridae (Hayward & Cook 1979). C. coronata differs from other Heliodomidae in colony form, budding pattern, avicularian morphology and mandible length, and in ovicell structure. However, the discovery of one species from Hawaii, C. spiralis, which has spirally budded colonies (Chimonides & Cook 1994), allows Cranosina to be provisionally assigned to the Heliodomidae, although it almost certainly requires a family grouping of its own.

Cranosina coronata encrusts shell and coral without any markedly spiral patterning. Zooids have a thick, brown cuticle forming the frontal membrane and avicularian mandibles. The most noticeable feature is the rim of large pore chambers at the base of the vertical zooid walls. The avicularia are laterally orientated and have a elongated mandible which is hooked terminally, and may have lateral serrations or expanded wings of cuticle on either side. Embryos are brooded in shallow ovicells which are little more than an expansion of the distal wall; but, like those of the other genera, are closed by the operculum. Brooding zooids may be slightly raised distally (Fransen 1986).

Cranosina coronata has a very wide reported distribution, and some populations show correlated sets of differences which may mean that they are referable to distinct taxa (Chimonides & Cook 1994). Specimens have been recorded from the north and east Indian Ocean to Japan, and the Philippines and New Guinea. One population has been found more than once in the Caribbean (Fransen 1986). C. coronata has been reported, as Biflustra, by MacGillivray (1891), from Western Australia and the Torres Straits (Harmer 1926), and from Queensland and the Great Barrier Reef (Hastings 1932, Ryland & Hayward 1992).

Diagnosis

Colony small, lightly calcified, encrusting minute substrata, such as a sand grain, becoming a little free peripherally, but without basal coelomic compartments. Zooids budded radially or spirally, cryptocyst narrow, opesia large, rounded. Avicularia interzooidal, usually rigidly patterned, with a very long, setiform mandible. Brooding zooids with large terminal ovicells.