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Bryozoa
Microporella morrisiana (Busk, 1859)
Nomenclature
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Family: MicroporellidaeGenus: Microporella
SUMMARY
Colonies are multiserial, forming encrusting unilamellar sheets. The growing edge is stepped and reveals large distal and distolateral pore chambers around the newly budded zooids. The ancestrula is tatiform with an egg-shaped opesia about 0.17 mm long by 0.12 mm wide and surrounded by 9 spine bases, the most proximal of which is in the midline of the zooid. Two distolateral buds are apparently produced from the ancestrula, the remaining four periancestrular zooids budding from post-ancestrular zooids. Autozooids from the zone of astogenetic change are smaller than subsequent autozooids but otherwise identical, supporting a single adventitious avicularium.
Autozooids are about 0.44-0.50 mm long by 0.34-0.45 mm wide, elongate rhomboidal in outline shape, the proximal and distal sides markedly shorter than the two proximolateral and two distolateral sides. The frontal shield is a convex cryptocyst evenly perforated by pseudopores and marginal areolar pores, and coarsely pustulose. The orifice is hemielliptical with a straight proximal edge, wider than long, averaging about 0.07 mm long by 0.10 mm wide. There are normally 4 but occasionally 5 oral spines. The crescent shaped ascopore is surrounded by a thick, transversely elliptical wall often more raised proximally than elsewhere. Ovicells are broken in all available specimens.
Adventitious avicularia are borne on all budded autozooids, singly, either on the left or right side of the zooid, positioned midway between the ascopore and the mediolateral corner of the zooid. They are directed distolaterally and have a semielliptical opesia, a calcified crossbar, and a triangular rostrum with slightly concave edges which is raised towards the channeled tip of the avicularium.