Family OTIONELLIDAE Bock & Cook, 1998

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Family OTIONELLIDAE Bock & Cook, 1998

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Otionellidae was introduced by Bock & Cook (1998) for the genus Otionella, which was restricted to its American, Eocene representatives, the genus Helixotionella, and Otionellina, which included all the Australasian species hitherto assigned to Otionella. The genus Petasosella, which included several Tertiary and two Recent taxa, was also added to the family, as was the genus Kausiaria, which had two fossil species. The family thus includes five genera with a wide temporal and geographic range, and species with spiral as well as radial budding patterns.

In general, zooidal opesia are small and rounded, although they are large in Kausiaria and subtriangular in Petasosella, where they may also have opesiules. Avicularia are often large, with an open or cribriform opesia, condyles are paired, often fused at the tips, and asymmetrical. Mandibles are usually elongated, expanded and marginally serrated, but do not have the hooped strengthening structures of Selenaria. Brooding zooids are often large, with wide opesiae and opercula, but may be undifferentiated from autozooids. They occur in submarginal and marginal series in Otionellina and Helixotionella, but are scattered in other genera. No morphologically polymorphic male zooids have been found. In Otionellina and Helixotionella, the peripheral avicularia of mature colonies may encroach onto the basal surface, and have mandibles which differ from those occurring frontally.

Colonies are not very large, and are often thickened basally and 'bun-shaped'; cloning by regeneration from small fragments occurs in some species of Otionellina and Petasosella. The family includes a very wide range of morphologies, which at one end approach those of some Cretaceous species of Lunulites, in Otionellina exigua. At the other end of the range, one species, O. affinis, resembles Selenaria in the characters of its avicularia. The genera Helixotionella and Otionellina share a distinctive early astogenetic pattern in which the ancestrula has one distal and one proximally placed avicularium.

The genus Otionellina is known from New Zealand and Australia, four species occurring from the Tertiary and/or Recent of both regions. No fewer than 12 species are known from Australia, 6 of which are found as fossils only, with a Late Eocene to Oligocene range. Five species have a Tertiary to Recent range, and only one, minute species, O. minuta, which has mature colonies less than 2 mm in diameter, has a Recent distribution only (Cook & Chimonides 1985; Parker & Cook, 1994, Bock & Cook 1999). The great majority of Australian records is from Bass Strait and South Australian waters, the only area to have been systematically examined for lunulite species. However, there are some records from Western Australia, Queensland and New South Wales, all from a depth range varying from 30-100 m. Autozooids in Otionellina have a small rounded opesia, and those of the brooding zooids are peripheral and enlarged. Most variation among species occurs in avicularian morphology. Most species develop avicularia at the periphery which open onto the basal surface. The mandibles of these avicularia are often far less robust than those on the frontal side. Unlike living species of Selenaria, locomotion does not occur: colonies of Otionellina have been seen only to clean the upper surface and stabilise the colony with the avicularian mandibles (Cook & Chimonides 1978).

In Helixotionella (Cook & Chimonides 1984b) all colonies are budded, at the earlier astogenetic stages at least, in a pair of interdigitating spirals. The genus is known only from Australia, and includes H. spiralis and H. scutata, which occur from Western Australia and South Australia, from a narrow depth range of 137-148 m. Both species have a fossil record from Victoria, H. scutata occurring in the Miocene, and H. spiralis in a large number of localities from the Late Eocene to the Pliocene (Bock & Cook, 1999). H. rubra has larger colonies and is known, rarely, from New South Wales and Queensland, from 48 - 93 m.

The genus Petasosella resembles Otionella sensu stricto in its early astogeny and large avicularia, which often have an extensive opesia. The autozooids have subtriangular to oval opesia and distinct female and male zooids have not been recognised from skeletal evidence. Recent species have scattered embryos in undifferentiated zooids. The avicularian mandibles are long and have narrow, lateral serrated wings. In P. moderna they greatly resemble those of Otionellina squamosa. Petasosella was well represented in the Victorian Tertiary (Cook & Chimonides 1985) and is known today principally from Bass Strait and South Australia westward across the Great Australian Bight, where two species, P. moderna and P. parkeri occur (Bock & Cook 1998).

The genus Kausiaria has no Recent representatives. It possesses an interesting mosaic of characteristics which appear, scattered among the other lunulite genera. Colonies appear to have no initial substratum, and are heavily calcified. Avicularia are small and have alternating symmetries. The genus ranges from the Late Eocene to the Miocene of Victoria (Bock & Cook, 1998).

Diagnosis

Colony free-living, cup-shaped or lenticular, solid or hollow basally, budded radially or spirally from ancestrula encrusting sand grain. Basal surface with traces of extrazooidal compartments, and marginal avicularia in some species. Zooids usually with a small, rounded to bell-shaped opesia. Colonies include autozooids and brooding zooids, which are sometimes enlarged and marginal. Avicularia budded among zooids, sometimes enlarged and in radial series, mandibles elongated, with lateral expansions, or setiform. Colony regeneration from small fragments possible.Colony free-living, cup-shaped or lenticular, solid or hollow basally, budded radially or spirally from ancestrula encrusting sand grain. Basal surface with traces of extrazooidal compartments, and marginal avicularia in some species. Zooids usually with a small, rounded to bell-shaped opesia. Colonies include autozooids and brooding zooids, which are sometimes enlarged and marginal. Avicularia budded among zooids, sometimes enlarged and in radial series, mandibles elongated, with lateral expansions, or setiform. Colony regeneration from small fragments possible.