Family VESICULARIIDAE Hincks, 1880

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Family VESICULARIIDAE Hincks, 1880

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Vesiculariidae was introduced by Hincks (1880) in the British Marine Polyzoa, for the genus Vesicularina, which is not known from Australia, although its colonies somewhat resemble those of Amathia (see below), having long, spinous kenozooids at the ends of branches. Embryos are brooded, usually singly, in the tentacle sheath, and there are usually 8-10 tentacles. Three genera occur from Australia and exhibit increasing integration, or colony control, in their budding patterns.

The first is the genus Bowerbankia, which has creeping stolons and semi-erect branches, with the cylindrical autozooids budded irregularly in small groups. The autozooids have a prominent gizzard. The records from Australia have not been fully documented, but this essentially northern genus is probably represented by fouling forms like B. gracilis and B. imbricata, both of which occur in New Zealand (Gordon & Mawatari 1992). The record given by Brock (1985) is not of Bowerbankia, but of Buskia. A species of Bowerbankia, B. antarctica, with very large zooids, was described by Winston & Hayward (1994) inhabiting the empty skeletons of calcified bryozoans from the Antarctic.

The second genus is a monospecific one, and is also part of a world-wide fouling fauna. Colonies of Zoobotryon verticillatum are characterised by their long chains of semi-transparent, bluish gelatinous autozooids and somewhat flaccid, very wide stolons, which may exceed a metre in length. The autozooids are arranged in two almost continuous series on either side of each stolon (Bock 1982). They have 8 tentacles and a gizzard. Larvae are brooded in the tentacle sheath and are very large (0.50 mm in diameter). Another unusual feature is that colonies are deciduous, losing autozooids at the onset of unsuitable conditions. Small sections of creeping stolon may also become thick-walled and opaque and function as hibernacula, growing multiple stolon kenozooids when conditions improve. The ancestrular development has been described by Zimmer & Woollacott (1977). A pre-ancestrula is first produced from metamorphosis of the settled larva. This produces a stolon which forms an adhesive disc on the substratum. The preancestrula is then lifted off the substratum by further growth of the stolon and concludes its development.

Z. verticillatum is a major fouling species (Gordon & Mawatari 1992), and it is interesting that colonies themselves produce an anti-fouling product which is able to discourage epizoic species growing on younger parts of the colony (Dayton, 1994 New Scientist). The older parts of colonies however, are usually the substratum for other bryozoans, particularly species of Bugula. West African colonies have a small, species-specific nudibranch predator, Favorinus (Cook 1985). The species was recorded from Moreton Bay by Macdonald (1857). Macdonald made no identification, but his description is so clear that the identification is obvious. This early record implies that it was either indigenous to Australia, or was introduced at a very early time in colonisation.

The genus Amathia is characterised by the relatively rigid, branching stolon systems and regularly patterned groups of cylindrical zooids which are superficially arranged in biserial rows, towards the end of each section of stolon. The zooids are connate for much of their length and may occur in short 'tooth-brush' like groups, or extensively spiral formations (Chimonides 1987). Each species appears to have a distinctive budding pattern which includes bifurcations, trifurcations and even tetrafurcations of the stolon structure, and may also include terminal spinous kenozooid patterns. Rhizoids arise at the more proximal parts of stolons and grow backwards to anchor the colony as it enlarges.

Like Bowerbankia, the tentacle numbers range from 8-10; a gizzard is present but is not usually as prominent as in Bowerbankia. Colonies may grow to more than 10 cms in diameter and height, and Chimonides (1987) noted that in some species the zooid groups were arranged to open within the relatively sheltered internal space, formed by the branches. Although they have been collected from greater than 500 m depth, species are generally from shallower waters, less than 50 m, and often from exposed localities, where current velocities are high (Bock 1982). The older parts of colonies are the substratum for many epizoic species, including bryozoans (Gordon & Mawatari 1992).

Larvae are brooded in the tentacle sheath. The larva of Amathia has been illustrated, and the ancestrula and early budding described for Bowerbankia. The larva is elongated and coronate; the erect ancestrula possesses two precocious buds and these become kenozooidal stolons, which further attach and stabilise the colony before budding more stolons and autozooids (Zimmer & Woollacott 1977; Hayward 1985).

Associates of Amathia include the gastropod Microginella minutissima which lives on A. biseriata in Australia. The entire life cycle is spent on the bryozoan, the occurrence of which 'actually determines the mollusc's distribution' (Murray 1970; Chimonides 1987).

The genus Amathia has a world-wide distribution, but is particularly abundant and diverse in Australian waters. The genus was introduced by Lamouroux (1812) after the examination of Australian specimens, even though a European form became the type species of the genus (Chimonides 1987). Tenison Woods (1877; 1880), Kirkpatrick (1888b) and MacGillivray (1895) described a number of species from South Australia, Tasmania and Victoria, and Bock (1982) noted that about 14 species had been recorded from this region. Records of Amathia have been made from all Australian coasts except the Northern Territory, but the great majority is from South Australia, Victoria and Tasmania. It is interesting that four Australian species are known from South Africa (Chimonides 1987).

Amathia has been reported from the Late Cretaceous (Maastrichtian) of Europe as a bioimmurated fossil (Voigt 1972).

Diagnosis

Colonies very large, erect, branched, attached by rhizoids, or small and creeping. Zooids budded in contiguous groups from kenozooidal stolons, often regularly and profusely patterned. Orifices terminal, gizzard present or absent. Larvae brooded in the tentacle sheath.