Notes on the Family Lekythoporidae (Bryozoa, Cheilostomata) P. L. Cook Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD P. J. Hayward Department of Zoology, University College of Swansea, SA2 8PP Introduction (a) Cheilostome Ovicells In recent years, several kinds of cheilostome ovicell have been investigated, and the origins and relationships of the various body wall layers involved have been traced through ontogeny. As a result, it has become obvious that the ovicell, which may be regarded as all the walls defining and protecting the brood chamber and the contained embryo, has several very different origins. Ovicells may be derived wholly, or in part, from diverticula of terminal walls or from extensions of frontal walls and, or, frontal shields. They may be derived wholly, or in part, from one or more zooids. They may be modified, interzooidal, frontally budded kenozooids, or may be formed from one or more kenozooids budded from the maternal zooid, which produces the ovum, or from a sequentially distal zooid or zooids (see Cook, 1979 for brief review). The general term 'ovicell' may therefore be defined functionally, but not morphologically, and it appears that the protective coverings for brood chambers have often been evolved convergently and show only superficial similarities. All ovicells which have been investigated in detail, and all those which may be inferred by inspection to have analogous ontogeny, are 'distal' in position to the opening edge of the operculum of the maternal zooid. Generally, this 'distal' orientation is also the same as the direction of budding of zooids 'away from' the ancestrula as the colony develops. Even in colonies with 'reversed frontal budding' (where the distal part of the orifice is directed towards the ancestrular region, see below), the opening of the ovicell is placed close to the orifice of the maternal zooid, on that side of the operculum which opens to allow protrusion of the lophophore (see Cook & Lagaaij, 1976). This position is correlated with the position of the coelomopore through which the ovum passes to the exterior. In all cheilostomes which have been investigated, the coelomopore is placed at the base of the 'distal' pair of tentacles. Passage of ova into ovicells is achieved by protrusion of the lophophore and apposition of the coelomopore to the ovicell orifice (see Silen, 1 945). Proximally placed ovisacs, which are principally uncalcified have been reported in the anascan genus Aetea, but their ontogeny may be intussusceptive and quite unlike that of other known ovicells (Cook, 1977). Proximal calcified ovicells have also been described in several cheilostome ascophoran genera, which were grouped together in the family Lekythoporidae by Levinsen (1909), and further reviewed by Canu & Bassler (1929). The reported occurrence of 'proximal' ovicells infers that the position of the coelomopore, or at least the behaviour of the maternal lophophore, is radically different from all other cheilostomes in only one group, the Lekythoporidae. Such a difference would be fundamental, although it could be postulated for the genus Inversiula (Microporellidae), which is apparently equally aberrant, and where the operculum is hinged distally (see Bull. Br. Mus. nat. Hist. (Zool.) 45 (2): 55-76 Issued 28 July 1 983 55
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