Riscodopa hyalina, 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 : 1610

Riscodopa hyalina sp. nov.

(gures 13, 14)

HOLOTYPE. MOV F52874 , SEAS (South Eastern Australian Slope, ‘ Franklin’ Cruise), Station SLOPE 2 , oV Nowra , New South Wales, 34 ss 57.09 ¾ S, 151 ss 8.00 ¾ E, 503 m, 11 July 1986, epibenthic sled, bryozoa and shell bottom.

PARATYPES. MOV F52875 , SLOPE 2 as above, and MOV F52876 , SLOPE 56 , from 34 ss 55.79 ¾ S, 151 ss 08.06 ¾ E, 429 m to 34 ss 56.06 ¾ S, 151 ss 06.86 ¾ E, 466 m, 22 October 1988, epibenthic sled, muddy coarse shell bottom.

Etymology From hyalinos (Greek)—glassy, referring to the semi-transparent calci cation.

Description

Riscodopa with tatiform ancestrula with nine marginal spines. Colony fan-shaped at rst, becoming lunulitiform later in astogeny, ancestrula surrounded by a ring of six zooids. Autozooids small, semi-erect, very thinly calci ed; frontal shield with 20–40 pseudopores and two to four frontal septular pores. Primary ori ce large, with paired proximo-lateral denticles, and a small, variably shaped lyrula, which may occasionally be absent. Four oral spines, the lateral pair with large spine bases; no proximal mucro. Paired latero-oral avicularia, with subtriangular mandibles orientated laterally. Ovicells present, or developing on zooids of the third to fourth astogenetic generation. Basal walls with a single, large, multiporous septular pore, placed just distally to the centre, giving rise to a rhizoid.

Measurements

Length of ancestrula 0.42 mm. Length of zooids 0.31–0.52 mm. Width of primary ori ce 0.16–0.18 mm.

Remarks

The specimens comprise four colonies, two of which are fractured and incomplete. They measure 1.5, 3.0, 3.5 and 5.0 mm in diameter, and include nine, 30, 30 and 31 zooids, respectively. Only one colony ( MOV F52876 ) has a lunulitiform shape, and has the only complete ovicell present. This is prominent, longer than wide, with a straight proximal edge and nely tuberculate surface. The smallest colony, which has an ancestrula, has not yet developed a complete ring of primary zooids (gure 14). A single rhizoid appears to have been produced by one of the second generation zooids, but accumulations of particles make this diYcult to see clearly, and the colonies are so delicate that it is not possible to remove the cuticular parts without damaging the zooids. Numerous rhizoids, 1.0– 1.50 mm long, occur in the three larger colonies, each arising from one of the basal septular pores. The zooidal ori ces are the same size as those of R. parva , but appear proportionately larger because of the smaller extent of the frontal shield. Riscodopa hyalina lacks a proximal mucro, and the lateral denticles and lyrula are less strongly developed than in other species. The oral avicularia are also similar to those of R. parva , but are placed more proximally.