Large colonies, up to about 10 cm in diameter, which are tabular or somewhat hemispherical in shape. Vertically sectioned specimens reveal concentric layers composed of subcolonies united at their edges. The upper surface of each subcolony has bundles of zooids (fascicles) arranged in a stellate pattern. Individual fascicles are enclosed by exterior wall calcification, marked by the traces of zooidal boundary walls, and are subquadrate in cross-section. New subcolonies are formed through the upward growth and radial expansion of selected fascicles, which then develop their own fascicles on the upper surface and coalesce at their edges with neighbouring subcolonies to produce a new layer of growth.
Autozooids are long and polygonal in section, with apertures averaging 0.16 mm in diameter opening at the distal ends of the fascicles.
Gonozooids are rare, located between fascicles, roofed by smooth exterior wall, and irregular in shape. The ooeciopore has not been identified.
This species is the rarest of the four large globular cyclostomes found in the Coralline Crag, and is currently recorded from only one locality, Ramsholt Cliff. Colonies tend to be more tabular than those of the other three species (Blumenbachium globosum, Meandropora aurantium and M. tubipora) and the strong concentric layering visible in sectioned or broken colonies together with the cup-shaped morphology of the subcolonies invites close comparison only with the first of these species. However, B. globosum lacks the fascicles characteristic of M. debenensis, while the latter species never shows the pattern of polygonal ridges frequently developed on the outer surfaces of B. globosum colonies.
Pliocene, Late Zanclean–Early Piacenzian, Coralline Crag Formation, Ramsholt Member, Ramsholt Cliff, Suffolk, UK (Balson & Taylor 1982).