Family RHABDOZOIDAE MacGillivray, 1887

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• Rhabdozoidae Macgillivray, P.H. 1887. A catalogue of the marine Polyzoa of Victoria. Transactions and Proceedings of the Royal Society of Victoria 23: 187-224.

Introduction

The Family Rhabdozoidae contains the single species Rhabdozoum wilsoni Hincks, described in 1882. A distinct family for the genus was first named, without definition, by MacGillivray (1887). Levinsen (1909) recognised the similarity with the family Scrupocellariidae (Candidae herein), and the family Rhabdozoidae was not defined adequately until Gordon (1989) described material from New Zealand.

The Rhabdozoidae is characterised by its unique budding pattern, where a zooid in a branch is closed and develops a frontally budded tubular stalk which extends proximally to form a calyciform zooid. Further branches arise from the calyciform zooid (Cook & Bock, 1994).

The family is represented by a single genus and species, Rhabdozoum wilsoni, which occurs from shallow to upper slope depths (10-800 m) from southeastern Australia, Tasmania, and the South Island of New Zealand (Bock 1982; Gordon 1989).

Colonies erect, 5-6 cm high, profusely ramified, supported and anchored by a rhizoid mass. The ancestrula is erect, vase-shaped, attached by a minute basal disc; its opesia is terminal, surrounded by 14 long, jointed spines.

All branches are calcified, with thin, translucent imperforate calcification covered by transparent cuticle. The stalks leading to branches are weakly calcified and flexible. Zooidal branches are budded distally from the ancestrula, and are at first biserial, then becoming triserial to quadriserial, and bifurcating two to three times, forming a cluster of closely apposed branches. The origin of new branch clusters is unique. A closed zooid opesia develops a frontally budded, elongated calyciform zooid. This has a tubular proximal gymnocyst, which is spirally annulated at its origin and termination, and sometimes halfway down its length. It expands distally to form a calyx with a circular opesia surrounded by 12-16 long, jointed spines. This zooid buds a pair of distal autozooids which form the base of the next branch cluster. All branches have zooids in obliquely sloping series, most facing outward. All autozooids have an elongated, tubular gymnocyst, a small oval opesia and a pair of minute lappets beside the terminal operculum. Outward-facing zooids have 8 large, proximal, curved, jointed spines, decreasing with each astogenetic generation to two spines. Inward-facing zooids have a single distal-lateral spine only. Proximal spines may be replaced by a triangular avicularium with a swollen subrostral chamber and a hooked rostrum. The ovicell is hyperstomial, smooth, with a large frontal area, not closed by the operculum. Rhizoids arise from pores in the gymnocyst.

Diagnosis

Colony erect, profusely branched, attached by rhizoids, composed of calcified internodes connected by the modified gymnocysts of special, frontally budded zooids. Zooids with a long gymnocyst and opesia surrounded by long, jointed spines. Avicularia sessile. Ovicells hyperstomial with a frontal area

General References

Bock, P.E. 1982. Bryozoans (Phylum Bryozoa). pp. 319-394 in Shepherd, S.A. & Thomas, I.M. (eds). Marine Invertebrates of Southern Australia. Handbook of the Flora and Fauna of South Australia Adelaide : Government Printer Part 1 491 pp.

Cook, P.L., & Bock, P.E. 1994. The astogeny and morphology of Rhabdozoum wilsoni Hincks (Anasca, Buguloidea). pp. 47-50 in Hayward, P.J., Ryland, J.S. & Taylor, P.D. (eds). Biology and Palaeobiology of Bryozoans. Fredensborg : Olsen & Olsen.

Gordon, D.P. 1989. The marine fauna of New Zealand: Bryozoa: Gymnolaemata (Cheilostomida Ascophorina) from the western south Island continental shelf and slope. New Zealand Oceanographic Institute Memoir 97: 1-158

Hincks, T. 1882. Contributions towards a general history of the marine Polyzoa. X. Annals and Magazine of Natural History 5 10: 160-170

Levinsen, G.M.R. 1909. Morphological and systematic studies on the cheilostomatous Bryozoa. Copenhagen : Nationale Forfatteres Forlag 431 pp.

Macgillivray, P.H. 1887. A catalogue of the marine Polyzoa of Victoria. Transactions and Proceedings of the Royal Society of Victoria 23: 187-224

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