Riscodopa paucipora, Cook & Bock, 2002

Cook, P. L. & Bock, P. E., 2002, Notes on astogeny of some Petraliellidae (Bryozoa) from Australia, Journal of Natural History 36 (13), pp. 1601-1619 : 1608

Riscodopa paucipora sp. nov.

(gures 8–12)

HOLOTYPE. MOV P128374 , Late Eocene, Browns Creek , Victoria.

Etymology

From paucus (Latin)— few, and porus (Latin)—hole, referring to the lack of frontal pseudopores.

Description

Riscodopa with non-tatiform ancestrula. Autozooids almost vertical, ori ces occupying the major part of the frontal shield. Frontal shield imperforate except for a single series of marginal or submarginal pores, most of which appear to be frontal septular pores. Primary ori ce large, subterminal, with paired lateral denticles, and a narrow, hammer-shaped lyrula, which together de ne a pair of proximal sinuses. Five to six oral spines, proximal mucro small, with a terminal avicularium with a subtriangular rostrum, orientated proximally and frontally, and a complete bar. Paired disto-lateral avicularia on swollen subrostral chambers, orientated laterally. Basal surface of each zooid separated by a groove from its neighbours, with a curved lamina raised above its proximal end. Each wall with a crescent or small group of three to ve septular pores arranged transversely in the mid-line. Ovicell not found.

Measurements

Length of ancestrula 0.28 mm. Length of zooids 0.23–0.38 mm. Width of primary ori ce 0.17–0.19 mm.

Remarks

Only one colony has been found. The ancestrula is sunken; its basal wall is missing. The primary ori ce is so large that the ancestrula almost appears to be tatiform. Although slightly damaged, the ori ce shows one lateral denticle, which resembles a condyle, and a proximal avicularian mucro, but no trace of oral spines. The ancestrula is surrounded by a distal triad of primary zooids, and a proximolateral pair budded later in astogeny, one of which has an ori ce occluded by calci cation, which includes the spine bases. The zooid ori ces are so large, and the frontal wall so restricted, that the network of pseudopores typical of other species of Riscodopa is absent. The marginal series appear to be all septular pores. The paired avicularia are not raised on columnar processes as in R. biincisa . The presence of an avicularium on the ancestrula is unusual but has been reported in other species ( Hayward and Cook, 1979: 77). The basal septular pores diVer from those of R. biincisa in being more numerous and arranged in a crescent across the mid-line of the zooid. The curved proximal lamina is less robust, but similar to that occurring in some specimens of R. biincisa . It suggests that while the rest of the basal calci ed wall is an interior wall, the rhizoids of R. biincisa and R. paucipora may have had a swollen origin surrounded by a rim of exterior calci ed wall, which included several septular pores, like those of Parastichopora ( Cook and Chimonides 1981a) . The rhizoids of R. parva , R. cotyla and R. hyalina are numerous, but only one is produced by each septular pore.