Family SELENARIIDAE Busk, 1854

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Family SELENARIIDAE Busk, 1854

Compiler and date details

July 2001 - Dr Philip Bock

Selenariadae Busk, 1854.

Introduction

The family Selenariidae was first introduced by Busk (1854), as Selenariadae, and included the genera Cupularia (= Cupuladria), Lunulites and Selenaria, in that order. Cupuladria belongs to the family Cupuladriidae, and Lunulites has been revised to include species referred to two families, the Lunulitidae and Lunulariidae.

The family Selenariidae is here restricted to the genus Selenaria alone (Bock & Cook, 1998). Generally, and apart from some isolated, unrevised reports, the family is known only from Australasia, and with one exception, S. concinna, all records are exclusively from Australian waters.

Selenaria is characterised by the zonation of its colonies. The central ancestrular area has small zooids, which are frequently closed by a lamina of cryptocyst at sexual maturity, and are then incapable of feeding. They may provide a region of passive excurrent water involved in a colony-wide feeding current (Chimonides & Cook 1981). The next concentric zone in the radially budded astogenetic series is composed of autozooids. This is followed by a zone of brooding zooids, and mature colonies, which grow no further, are completed by a peripheral zone of male zooids, which have enormously long, paired, unciliated tentacles. These are controlled by very large muscles, and no viscera are present, so that male zooids are incapable of feeding. The skeletal characters of each of the different kinds of zooid are distinct and specific (Cook & Chimonides 1978).

Avicularia are usually large, far larger than the autozooids, in several species. They may have an open opesia, or a complete, porous cryptocyst, and are budded among the zooids in a distinct pattern. The setiform mandibles may be very long and are circular in section, strengthened by a series of hoops of thickened cuticle. Mandibles are slung on fused condyles which may be twisted to form an S- or C-shape. The mandibles are capable of movement in all planes and all directions over the colony surface. They are usually serrated, and in addition to cleaning the zooid frontals, and stabilising the colonies within and upon the sediment, are also able to sustain locomotion of the entire colony (Cook & Chimonides 1978; Chimonides & Cook 1981).

The autozooids are radially budded and are usually nearly as wide or wider than long, with an oval or subtriangular opesia. A significant number of species have a small opesia and paired proximal opesiules (Cook & Chimonides 1985). Brooding zooids are always larger than autozooids and are raised distally. In a few forms the distal edge of the opesia is considerably raised and flanged distally. The embryo is brooded in an interior ovisac, and small ovocytes are often found in the visceral coelom. The presence of sperm heads in these ovocytes suggests that precocious fertilization may occur, and the ovocyte will grow before eventual cleavage. Marcus (1938) has discussed this phenomenon in several species (Chimonides & Cook 1981).

Male zooids have a large cystid, which is filled by the withdrawn tentacles and the very large muscles which control them. Colonies frequently aggregate, and the extended male tentacles are the same length as the mature colony radius. When fully extended on all sides they double the diameter of the circle occupied by the colony. Sperm are disseminated from the tips of the tentacles which are protruded for only 2-10 seconds at a time, making rapid flickering movements and then being withdrawn. Complete withdrawal often takes several muscular contractions, and the tips of the tentacles are often twisted round one another before the very small male operculum can close.

The elongated tentacles and lack of viscera of the male zooids, together with their behaviour, is very similar to that seen in species of Hippoporidra (Cook 1985), and in Odontoporella adpressa (Busk), described by Gordon (1968). The colonies of both these genera are almost always, sometimes specifically, associated with gastropod shells inhabited by pagurid crabs. A similar association occurs between Hagiosynodos lata and gastropod shells (Cook 1985, as Hippopodinella; Bishop & Hayward 1989). It is not known if male zooids occur in H. lata, but nearly all specimens of Hippoporidra examined from west Africa encrusted shells inhabited by pagurids. It is interesting that similar male zooid morphologies and behaviour should occur in one anascan and one ascophorine family, where the colonies have the potential for mobility. In the cases of Hippoporidra, O. adpressa and Hagiosynodos lata, the locomotion is dependent upon the pagurid, whereas in Selenaria the colony itself is capable of sustained movement.

Species of Selenaria have been reported from all coasts of Australia. most commonly from 20 to 100 m depth, although some very shallow records occur from near Townsville (Chimonides & Cook 1981). There are 25 presently known Australian species, 10 of which occur only as fossils. Of the remainder, only one, S. occidenta from the northwest region, has no fossil record. All the other Recent species have a record extending to the Miocene at least, and five species are known from the Late Eocene to Recent (Bock & Cook 1999).

The great majority of species is known from South Australia and Bass Strait (Bock 1982 and Cook & Chimonides 1987), but this is probably because this is the only area where fine fractions of bottom sediment have been routinely examined.

Colonies are frequently the substratum for other bryozoan species such as Mollia patellaria which grow on the basal surface. A species of the ctenostome Sundanella has been found growing on the mandibles and on and within empty cystids of Selenaria (Chimonides & Cook 1981, Parker & Cook 1994).

The Selenariidae seem to have the closest relationship with some genera of the Otionellidae, particularly the genus Otionellina.

Diagnosis

Colonies free-living, cap-shaped or lenticular, budded radially from ancestrula attached to sand grain. Basal side well calcified, with extrazooidal radial compartments. Zooids arranged in concentric regions consisting of autozooids, female brooding zooids with a small distal chamber, and marginal male zooids. Autozoooids with depressed imperforate cryptocyst; opesia semicircular or subrounded; opesiules present or absent, or as opesiular indentations in the proximal margin. Brooding zooids submarginal in mature colonies, with elevated or reduced distal ovicell cover. Male zooids often with minute opesia with a distal tooth, very long, paired tentacles, complex muscle systems and no other viscera. Interzooidal or vicarious avicularia interspersed with zooids. Avicularia large, with long setiform mandibles slung from an asymmetric curved condyle system. Avicularian frontal wall may be porous, or with an open opesia.