Family THALAMOPORELLIDAE Levinsen, 1902

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Family THALAMOPORELLIDAE Levinsen, 1902

Compiler and date details

July 2001 - Dr Philip Bock

Thalamoporellidae Levinsen, G.M.R. 1902. Studies on Bryozoa. Videnskabelige Meddelelser fra Dansk Naturhistorisk Forening i Kjøbenhavn 54: 1-31 [21].

Introduction

The family Thalamoporellidae was first introduced by Levinsen (1902), but quoted again as a new family in 1909. Levinsen also referred all species which had earlier been assigned to the genus Thairopora to Thalamoporella. Some species which have been placed in both these genera are here referred to Diploporella, Marsupioporella or to Dibunostoma (see below). In addition, an aberrant genus of Thalamoporellidae, Hesychoxenia, introduced by Gordon & Parker (1991), which is known only from Australia, is also included here. The subfamily Hesyxocheniinae was introduced for this genus only, with all other genera placed in the subfamily Thalamoporellinae.

The family is characterised by zooids with a well-developed, porous cryptocyst, small rounded opesia, and paired, often asymmetrical opesiules. Raised, hollow, adoral areas occur on either side of the orifice. Many species are associated with algae or seagrasses, but others have erect, vinculariform or even nodal colonies. All genera posses calcareous spicules within the coelomic spaces of zooids. These may be numerous especially at the growing edges of encrusting expanses, and include two types, calipers and compasses. The spicules are bilaterally symmetrical and curved, or V-shaped with a very obtuse angle.

Brooding structures are varied, and not known in many cases. Bivalved ovicells occur in Thalamoporella, ovisacs are inferred for Thairopora and Diploporella, and proximally placed 'marsupia' are only suspected of having a brooding function in Marsupioporella. Nearly all genera, and the majority of species, have interzooidal avicularia, often occurring in distinct patterns among autozooids.

Species of Thalamoporella are found in warm, and warm temperate waters throughout the world. One species has been reported to survive in a salinity of 67.5‰ (Lagaaij & Cook 1973). Species of the other genera are limited to the Indo-west Pacific, and many are entirely confined to Australia.

The type species of the genus Thalamoporella has a problematical history, and a neotype was indicated for T. rozieri by Soule et al. (1992). Thalamoporella is characterised by autozooids with a rounded opesia, co-terminous overlying operculum, and a descending cryptocyst which forms asymmetrical opesiules inserted on the basal wall. Avicularia are often large, with a distinct proximal cryptocyst, which may have opesiules (Cook 1964). Mandibles may be acute or spatulate, and are directed distally.

The majority of species develops large, bivalved ovicells, formed by expansion of the hollow adoral areas. They are thus not homologous with most other forms of anascan ovicell, although Harmer (1926) noted the similarities in their structure with those of the genus Alysidium. Several embryos may be brooded simultaneously. The characters of the genus, and the structure of autozooids and avicularia have been thoroughly illustrated by Soule et al. (1992).

Thalamoporella was introduced by Hincks (1887) for T. rozieri from the Red Sea. The Australian fauna includes more than 10 nominal species, the first record being described as a form of Steginoporella rozieri by Hincks (1880). T. falcifera has small, curved avicularia and was recorded from Western Australia. Maplestone (1905) reported it from Lord Howe Island, but the avicularia in his illustration are not curved, and it may be another species.

Several of the species introduced by Levinsen (1909) as varieties appear to warrant specific rank and include T. granulata, T. prominens, T. sparsipuncta and T. stapifera, all from Queensland (Harmer 1926; Ryland & Hayward 1992). Colony forms vary from encrusting in T. stapifera to erect and nodal in T. prominens. Other species recorded from the Northern Territory or northern Queensland include T. hamata Harmer and T. novaehollandiae (Haswell 1881), which both have erect, tubular anastomosing colonies.

Harmer (1926) noted that the distribution of species of Thalamoporella in Australia was more northerly than those of Thairopora, and the records of T. granulata and T. stapifera from Heron Island are among the most southerly for the genus (Ryland & Hayward 1992).

Thalamoporella has a long fossil history extending from the Eocene of Sulawesi (Celebes) (Pouyet & Braga 1993); in Australia, several erect species occur from the Victorian Tertiary (Soule et al. 1992).

Nearly all species of genus Thairopora are exclusively Australian, except for T. lunti, and one aberrant species, T. harmeri, which has ovicells ( Soule et al. 1991). Thairopora forms strap-shaped encrustations on algae or seagrass, and the colonies do not develop ovicells. The genus was introduced by MacGillivray (1882), for four species described in 1869, from which Harmer (1926) selected Membranipora dispar as type species. M. mamillaris MacGillivray (1860) was also included in Thairopora, but was selected as the type species of the genus Pergensina by Jullien (1888). It does not appear to differ significantly from Thairopora and was placed in synonymy by Harmer (1926). Pergensina was not mentioned by Soule et al. (1991). The zooidal cryptocyst in Thairopora is formed by the partial coalescence of four calcified plates, which leave uncalcified sutures on their inner margins. The opesiules are formed by openings in these sutures. The opesia is distal and rounded, like that of Thalamoporella, and the operculum is also coterminous, and slightly raised above it. The sutures in the cryptocyst calcification appear to be correlated with the occurrence of species on flexible substrata.

Colonies are frequently budded in verticillate series, forming regular lateral rows across the substratum. In T. dispar, a series of very large zooids, with unilaterally enlarged adoral tubercles is followed by a row of alternating , much smaller autozooids and avicularia. This is followed by a row of slightly larger autozooids, before the pattern is repeated. The avicularia generally are orientated distally in all species, and have acute mandibles, which close upon a raised equivalent of the adoral areas of autozooids.

Six nominal species of Thairopora have been described from Western Australia, South Australia and Victoria, usually encrusting red algae; their distribution being distinctly more southern than that of Thalamoporella. One species, T. armata, has also been reported from New South Wales by Whitelegge (1889). Hayward & Ryland (1995) reported a new species, T. calcarata, from the Great Barrier Reef, growing on Sargassum, which develops large, branched, hollow adoral areas which overhang the frontal membrane.

The genus Diploporella was first established by MacGillivray (1881) using the preoccupied name Diplopora. In 1885 he emended the name. The type species is Membranipora cincta Hutton (1878), but this is a junior synonym of Cellepora alata Lamouroux (1821), as described by Gordon & Parker (1991c). D. alata was recorded, as Thairopora cincta, by Bock (1982). Although very similar to Thairopora, D. alata differs in having raised lateral 'alae' of gymnocyst which become very prominent. The adoral areas are also raised as spinous tubercles, which are unequally developed. D. alata and the closely similar D. woodsii (MacGillivray 1869) are widely distributed on algae from Western Australia to Victoria. Bock (1982) noted that brown and purple colonies of D. alata grew 'encircling stems of algae or the seagrass Amphibolis, the rows of zooids curved circumferentially'.

Another genus, Marsupioporella, was introduced by Soule et al. (1992) for Thairopora whittelli MacGillivray (1889) from South Australia. M. whittelli resembles Diploporella closely, but the lateral gymnocystal areas are raised and medially fused above the cryptocyst, forming a globular cavity proximal to the operculum. It is not known if these cavities function as brooding structures (Soule et al. 1991).

The genus Dibunostoma was introduced by Cheetham (1963) for Calpensia reversa Harmer (1926). D. reversa has small, paired opesiules, adoral areas, small, proximally orientated avicularia , and has been found to have coelomic calcareous spicules. Dibunostoma is thus certainly referable to the Thalamoporellidae. Thalamoporella expansa Levinsen (1909) was redescribed by Harmer (1926) from Torres Strait, and also belongs to Dibunostoma. The colonies are encrusting and the zooids have small paired opesiules and the small avicularia are orientated proximally, like those of D. reversa. Dibunostoma appears to be a senior synonym of Thalamotreptos Soule et al. (1991), as noted by Gordon & Parker (1991).

Hayward & Ryland (1995) have recently described a new species of Thairopora from Heron Island, Great Barrier Reef, encrusting Sargassum.

One further genus of Thalamoporellidae is the monospecific and aberrant Hesychoxenia, introduced by Gordon & Parker (1991) for Membranipora praelonga MacGillivray (1890). H. praelonga encrusts seagrasses from western and southern Australia. The autozooids, and marginal kenozooids, possess numerous calcareous spicules. The elongated autozooids are membraniporiform, and the frontal membrane is underlain by a very thinly calcified, bilobed cryptocyst. Opesiules, avicularia and ovicells are apparently absent. Colonies have a distinctive astogeny, which includes the development of undifferentiated 'giant buds' at the periphery (Gordon & Parker 1991).

The closest relatives of Thalamoporellidae appear to be Siphonoporella and Labioporella, as well as the Steginoporellidae.

Diagnosis

Colonies erect or encrusting. Zooids subrectangular, with extensive perforate cryptocyst; opesia semicircular or with a broad convex proximal margin, with an coincident operculum. Opesiules large, paired or single, delimiting a central or lateral polypide tube. Single or paired tuberculate prominences may occur at the distal end of a zooid. Avicularia vicarious, with spatulate, pointed or triangular mandible. Ovicells prominent, inflated and thinly calcified, or absent. Internal calcareous spicules normally present.