Stephanocyathus (Stephanocyathus) imperialis, Cairns, 2004

Cairns, S. D., 2004, The Azooxanthellate Scleractinia (Coelenterata: Anthozoa) of Australia, Records of the Australian Museum 56, pp. 259-329 : 285-286

Stephanocyathus (Stephanocyathus) imperialis n.sp.

Figs. 4C–F

Records/Types. Holotype: Cidaris II 15–1, MTQ G55640 . Paratypes: Cidaris II 15–1, 2: 1, MTQ G56420, 1 , USNM 1008827 ; Cidaris III, 14–2, 3, MTQ G55642 and 56421. Type Locality: 13°29.08'S 147°12.68'E (Coral Sea off Cape York Peninsula , Queensland), 2442–2457 m .

Description. Corallum bowl-shaped, almost hemispherical, the holotype measuring 22.6 mm in CD and 9.3 mm in height. Most of theca worn or chalky in texture, only a thin band 2.5–3.0 mm wide adjacent to calice and corresponding to the region of edge zone is smooth and porcellaneous. In well-preserved coralla, theca corresponding to C1–3 within the region of the edge zone bears small granules arranged in a continuous zig-zag pattern. Calice circular and coarsely serrate in lateral view, each septum rising from a equilateral triangular-shaped base ( Fig. 4E). Corallum white.

Septa hexamerally arranged in 4 to 5 cycles, the fifth cycle never complete. There seems to be no absolute relationship between CD and number of septa, at least in the 6 specimens available for study, as the largest corallum (23.4 mm in CD) has only 48 septa, whereas the smallest corallum (18.4 mm CD) has 58 septa, and those of intermediate size have a range of 42 to a maximum of 60 septa. S1 only independent septa, extending to the columella without merging with any other septa. S1 only slightly exsert (1.8 mm) and rather narrow, following the curvature of the theca, but near the columella each S1 bears 1 or more poorly differentiated paliform lobes which have highly sinuous axial edges. S2 slightly less exsert (1.3 mm) but similar to the S1, also reaching the columella and bearing sinuous poorly-defined paliform lobe (s). Remaining septa (S3–5) equally exsert (1.2 mm), the S3 similar in shape to the S1– 2, but their axial edges loosely merging to their adjacent S2 near the columella. If unflanked by S5, the S4 extend about 2/3 the distance to the columella before loosely fusing to their adjacent S3; if flanked by a pair of S5, the S4 are similar in size and shape to an S3, and the S5 are then the smallest septa, similar in size and shape to an unflanked S4. Fossa relatively deep, containing an elongate columella consisting of 10–15 small intermingled papillae that are fused onto a circular base.

Remarks. Stephanocyathus imperialis differs from the three other congenerics known from the Australia region ( S. regius , S. platypus , and S. sp. sensu Cairns & Parker, 1992) in having poorly-developed, highly sinuous paliform lobes; a coarsely serrate calicular edge; and a smaller corallum with fewer septa. It is also found much deeper than the other three species.

Etymology. imperialis, Latin for “of the emperor”, in keeping with the names of several other species in this genus, as well as the genus name, that relate to aspects of royalty.

Distribution. Known only from the Coral Sea off Cape York Peninsula, 2436–2474 m.