Family BEANIIDAE Canu & Bassler, 1927

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Family BEANIIDAE Canu & Bassler, 1927

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The Family Beaniidae includes a group of loosely adherent, weakly calcified bryozoans with zooids linked by connecting tubes. Colony growth may be linear or spreading. The zooids are elongate bowl-shaped, with a frontal surface of membrane coinciding with the opesia. Marginal spines are present in many species, and pedunculate avicularia are also found in some species.

The family Beaniidae includes numerous species, and has representatives in all seas except the high Arctic. Eighteen nominal forms have been described from Australia (Harmer 1926; Hayward & Ryland 1995), and nearly as many from the Antarctic, subantarctic and southern oceans (Hastings 1943; Hayward 1995). The Beaniidae has been included in both the Bugulidae and the Bicellariellidae in the past, but was separated by Canu & Bassler (1927) for the genus Beania and its type species B. mirabilis Johnston (1840). Many of the species included are reputed to have very wide distributions, but require investigation: they have been illustrated in detail by Harmer (1926), Hastings (1943), Maturo (1966) and Fransen (1986).

The family is characterised by its discrete zooids, which are interconnected by calcified tubes which originate from pore-plates in the vertical walls. Colonies are semi-repent, anchored to, and supported above the substratum by rhizoids. The colony form depends to a great extent on the number and position of the interconnecting tubes, which are specific. Colonies in which the zooids have four to six tubes, placed proximally, have closely packed networks of erect zooids which form a turf on shells, stones, etc. Species with only one or two tubes, placed in the middle of the vertical walls, tend to be repent and form much more diffuse networks. Uniserial species form inconspicuous, runner-like colonies among other epizooic species. Most species are from shallow water, but one, at least, is abyssal, and occurs from western New Zealand (Gordon 1986; Cook 1988), and might well be found to be part of the deep-water Australian fauna in the future. The maximum known depth for Australian waters is 1264 m, off the eastern coast of Tasmania (unpub. record).

Several genera other than Beania have been proposed for different species in the past (Bassler 1953). Of these, only the genus Stolonella Hincks (1883) seems to differ sufficiently from all other species to maintain its separate status. S. clausa, the only species, has a semi-repent, jointed, kenozooidal stolon, anchored by branched adhesive discs. The zooids are isolated, each arising from the stolon and attached to it by an extended proximal, tubular gymnocyst. The frontal membrane is completely covered by a shield of medially fused, overarching spines, and there are four short oral spines. S. clausa was described growing, sometimes luxuriantly, over 'Fucus' from western Australia and Hincks remarked that it 'may safely be pronounced one of the loveliest of Polyzoa'. A closely similar species, B. pectinata, with an adherent, but not jointed, kenozooidal stolon, and zooids with an unfused frontal shield of spines, has been described from the Great Barrier Reef (Hayward & Ryland 1995).

Zooids of all species are boat-shaped, with an extensive frontal membrane and a proximal cryptocyst which is not usually large. Calcification is very thin, and although there are usually oral spines, marginal spines may be absent. A few species have numerous marginal, and even basal spines.

Avicularia are pedunculate, and when present are most frequently paired and oral. Although most are of the bird's-head type, some may have elongate, hooked mandibles. Embryos may be brooded in conspicuous, hyperstomial ovicells, or in interior ovisacs. The brooding method of many species is unknown.

Several species were first described from Australia, and a summary of their characters was given by MacGillivray (1886, 1890). Gordon (1984, 1986) has redescribed many species with an Australasian distribution, and new forms from Queensland have been described by Ryland & Hayward (1992), and Hayward & Ryland (1995). Two widely distributed species show the range of characters which may occur. B. mirabilis occurs in tropical to temperate waters in all oceans. It has uniserial colonies and the zooids have short marginal spines (Fransen 1986). B. magellanica has colonies forming a dense network, each erect zooid having six interconnecting tubes. There are no marginal spines, but the paired, oral avicularia are very large (Bock 1982). B. magellanica 'seems to be practically ubiquitous in tropical, subtropical and temperate sea' (Ryland & Hayward 1992). Although it has a circum-polar distribution in the subantarctic, it does not extend into the Antarctic (Hayward 1995). There are two endemic Antarctic species including B. erecta, which has even larger avicularia than B. magellanica (Hastings 1943; Hayward 1995).

Harmer (1926) suggested that the species of Beania might illustrate an evolutionary series, beginning with those with six interconnecting tubes, and ending with the uniserial forms. Despite the fragility of colonies, the Beaniidae has a fossil record. Labracherie & Sigal (1975) listed a species from the Lower Eocene of the Indian Ocean, and B. bermudezi was described by Lagaaij (1968) from the Middle and Upper Eocene of Cuba. The zooids had four tubes, marginal spine bases and a small ovicell. Avicularia were not evident.

Diagnosis

Colony of spreading sheets or uniserial chains of disjunct zooids, largely adnate, attached by rootlets to the substrate. Zooids weakly calcified, with extensive frontal membrane. Marginal and distal spines often present. Pedunculate avicularia present in many species, or absent. Ovicells generally absent, but occur as distal extensions of the zooid in some species.