Family PETRALIIDAE Levinsen, 1909

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Family PETRALIIDAE Levinsen, 1909

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Petraliidae was introduced by Levinsen (1909) for one genus, Petralia MacGillivray (1869), who erected it for P. undata from Victoria. The family is characterised by its unilaminar, curved, fan-shaped and fenestrate colonies, which are anchored in sandy sea-bottoms by numerous soft cuticular rhizoids.

The autozooids are well calcified, with a cryptocystidean frontal shield with frontal septulae and numerous pseudopores. The orifice is circular, and sometimes bears teeth, or a proximal lyrula. Avicularia are usually present near each orifice, and in P. undata, a vicarious avicularium is placed on the proximal side of each fenestra. On the 'basal', convex colony face, the zooids are marked by the insertion of lateral walls, and the basal walls are pierced by numerous septulae, which may give rise to rhizoids on the proximal side of the colony. Colonies arise from a minute triad of zooids and are anchored progressively as they become larger. Fenestrae are produced regularly by the bifurcation and anastomoses of zooidal series, which are 4-5 zooids wide.

There are three Australian species. P. undata forms a curved fan, with the convex 'basal' side upward, and the concave zooidal side inclined downward. Colonies may grow to a width of 15 cms, and are dark, purplish-brown in colour with lighter growing edges (Bock 1982). The orifice is circular; ovicells are large, prominent and finely porous. They are not closed by the operculum. P. livingstonei Stach (1936) was introduced for specimens from South Australia called P. undata by Livingstone (1928). It differs from P. undata in its smaller, cream coloured colonies, which have large, more elongated fenestrae. The autozooids have fewer pseudopores and the orifice has a proximal lyrula. Although the lateral avicularia adjacent to a fenestra are enlarged, there are no vicarious avicularia.. The ovicells resemble those of P. undata. The third species is P. ingens, which was described by Harmer (1957) for a species from west of Waigeu Island, northwest New Guinea. In this species the orifice contains two small teeth, the 'extraopercular teeth' of Levinsen (1909), similar in appearance to condyles, delimiting a rounded pseudosinus. The structure is not homologous with the condyles and sinus in lepralioid/cryptocystidean bryozoans such as Schizoporella. Harmer described the rare occurrence of a vestigial lyrula in P. ingens. This species is present in dredged samples from offshore western Australia, in the collection of the Queensland Museum.

P. undata has been found on areas of stabilized sandy substrata from South Australia and Victoria. It is 'particularly abundant near Port Phillip Heads' (Bock 1982). P. livingstonei has been reported from New South Wales and South Australia. The record from Tasmania given by Stach (1936) was of material in the Australian Museum, and this was later reexamined and identified as P. undata by Wass & Yoo (1983).

Diagnosis

Colony well calcified, brightly pigmented, erect, unilaminar, curved, fan-shaped and usually fenestrate, anchored by rhizoids. The zooids have lepralioid frontal shields with numerous pseudopores, the orifice is circular, with some marginal teeth or a lyrula. Avicularia small, oral, and adventitious, or large, sub-fenestral and vicarious. Ovicells prominent, hyperstomial and finely porous.