Family MONOPORELLIDAE Hincks, 1882

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Family MONOPORELLIDAE Hincks, 1882

Compiler and date details

July 2001 - Dr Philip Bock

Monoporellidae Hincks, 1882.

Introduction

The genus Monoporella is represented by a species complex usually referred to as M. nodulifera. Although Hayward (1974) concluded that several of the taxa referred to by other names could all be assigned to M. nodulifera, comparison of SEM illustrations shows that there are significant differences between Australian and European populations.

Colonies are encrusting and unilaminar, rarely forming large expanses, and following irregularities in the substratum in small lobes several zooids wide. The autozooids have an extensive cryptocystal frontal, with an opesia and an operculum coterminous with the primary uncalcified orifice. The cryptocyst is raised around the operculum to form a secondary calcified orifice. The cryptocyst has minute pores, and a central ridge with paired lateral depressions. There are two small opesiules. The operculum is dark brown and the orifice is bordered by 2-8 black spines.

The ovicells of Monoporella are unique among cheilostome Bryozoa, and have been described in detail by Cheetham & Cook (1983). No fewer than four zooids are involved in accommodation of the embryo, an example of colony integration. The ovicell is very large, its frontal shield is a cryptocyst derived by proximal development from the cryptocyst of the zooid distal to the maternal zooid. The cryptocyst is deficient laterally, leaving paired slits. The frontal membrane of the distal zooid extends proximally to cover the entire ovicell, except for the slits. The ovicell cavity extends distally from the end of the maternal zooid, and is closed by the operculum. The orificial spines of the maternal zooid are hidden by the ovicell cover. The pairs of disto-lateral zooids bordering the ovicell are modified. Their cryptocysts are depressed on that side which borders the adjacent slit in the ovicell cover, but the cuticle of their frontal membranes is thickened on that side and closes the slit. As the calcification of the orifice area of the maternal zooid increases, it closes the orifice above the spines, and the embryo cannot escape in the normal way. The embryo is a large one, filling the ovicell cavity. Its only route is by means of one of the lateral slits, but this can only be opened by depression of the frontal membrane of the distal lateral zooid and the modified lateral depression in its cryptocyst. Thus in both structure and behaviour, Monoporella exhibits integrative features not found elsewhere.

Monoporella is distributed from the Aegean Sea and eastern Mediterranean, the Cape Verde Islands, and the Torres and Bass Straits (Hincks 1881; Harmer 1926; Hayward 1974).

Maplestone (1911) illustrated a species very close to M. nodulifera from the Tertiary of Victoria.

Diagnosis

Colony encrusting. Zooids with flat to convex cryptocyst with numerous pores and a pair of small opesiules proximal to opesia. Opesia semicircular, coterminous overlying operculum; distal oral spines present. Ovicellular complex contributed to by four zooids, with slit-like lateral openings. No avicularia.