Woodipora holostoma (Wood, 1844)
Colonies are multiserial, forming encrusting sheets, up to 11 mm in diameter in the holotype which encrusts the concave interior of a bivalve shell. Early astogenetic stages are unknown (damaged in the holotype).
Autozooids are broad, about 0.6 mm long by 0.4 mm wide, ovoidal to rhomboidal in outline shape with convex distal and concave proximal edges. The frontal wall is an extensive, slightly depressed, granular cryptocyst containing a pair of oval opesiules with their long axes oriented approximately tangentially to the proximolateral corner of the adjacent opesia, A thick, raised, densely granular mural rim surrounds the cryptocyst. The opesia is ovoidal, slightly broader than long, the length approximately 0.18 mm, with a proximal edge more gently curved than the distolateral edges. Ovicells have not been observed.
Vicarious avicularia are developed at zooid row bifurcations, constituting one of the two daughter zooids. They are approximately the same length as an autozooid but significantly narrower, measuring about 0.3 mm in width. The cryptocyst is granular and contains small, comma-shaped marginal pits at the shoulders on either side of the rostrum, the latter having the form of a high rounded arch. The opesia is longitudinally elliptical, variably and slightly constricted at approximately mid-length a little below the level of the comma-shaped pits. Autozooids distal and lateral of an avicularium tend to be slightly torqued such that the axes of their opesia are oriented towards the avicularium.
This rare species most closely resembles Manzonella fissurata. However, the oval opesiules of Woodipora holostoma contrast with the long, curved opesiules found in M. fissurata, and the autozooids are more equidimensional in shape. Although vicarious avicularia are developed at zooidal row bifurcations in both of these species, they have trifoliate opesia in M. fissurata but elliptical opesia in W. holostoma.
Pliocene, Late Zanclean–Early Piacenzian, Coralline Crag Formation, Suffolk, UK. The provenance of the holotype is unknown. A second, poorly preserved specimen of this species in the K. J. Tilbrook Collection was collected from the Aldeburgh Member of Aldeburgh Hall.
Also recorded by Lagaaij (1952, p. 38) from the Scaldisian of The Netherlands; see Bishop & Hayward 1989, figs 29-30 for SEM micrographs of one of Lagaaij’s specimens.