Flabellum (Ulocyathus) sexcostatum Cairns 1989

Flabellum (Ulocyathus) sexcostatum

DESCRIPTION.—Corallum laterally compressed basally but campanulate distally, the change occurring at a height of 12–15 mm. Basal thecal edge angle 55°–75°, upper thecal edge angle 115°–130°. Inclination of basal lateral faces 61°–73°, upper thecal faces only 29°–36°. Largest paratype 49.3 × 30.4 mm in calicular diameter and 40.4 mm tall. Theca fragile, white to pale reddish brown. C1 ridged (up to 2 mm high) for about 15 mm beginning at a height of 12–15 mm and corresponding to the region at which the thecal edges and faces are inflected upward. In the holotype, C2 are also slightly ridged, but much less than the C1. Pedicel elliptical in cross section, about 2.0 × 1.5 mm in diameter, the greater diameter aligned with the principal costae. Ratio of GCD: LCD = 1.5–1.6.

Septa hexamerally arranged in five cycles, the fifth cycle complete at a greater calicular diameter of about 45 mm. S1–2 large and exsert, with straight, vertical inner edges. S3 about size of S1–2, each forming a small triangular apex about 1.5 mm tall. S4 about width of S3 but slightly more exsert than S3, each S4 together with its adjacent S1 or S2 projecting upward in a triangular extension 4–5 mm tall. S5 small, extending only about distance down theca. Septal granules small and sparse, about 0.11 tall.

Fossa extremely deep and narrow. Columella rudimentary, formed by a loose fusion of the lower, inner edges of the S1–2; inner edges of S3 attain the columella but do not significantly enlarge it.

azooxanthellate

685-1121 m