Sphenotrochus excavatus Tenison-Woods, 1878

Cairns, S. D., 2004, The Azooxanthellate Scleractinia (Coelenterata: Anthozoa) of Australia, Records of the Australian Museum 56, pp. 259-329 : 300

Sphenotrochus excavatus Tenison-Woods, 1878

Figs. 9G,H

Sphenotrochus excavatus Tenison-Woods, 1878b: 308 , pl. 4, figs. 1A–C (NSW).– Squires, 1961: 19 (listed).– Wells, 1964: 109 (listed).– Veron, 1986: 606 (listed).–Cairns, 1997: 25 (listed).

New records. None.

Types. The holotype is deposited at the Macleay Museum; it is uncatalogued. Type Locality: Port Jackson , New South Wales, depth unknown .

Redescription of holotype. Corallum 5.80× 4.07 mm in CD ( GCD:LCD= 1.43) and 9.44 mm in height. Costae continuous (not fragmented), all costae but the 4 C3 flanking the medial C2 reach the base, those 4 C3 reaching only about 90% of that distance. Costae on thecal faces wide near calice (0.38 mm), narrowing to about 0.16 mm near the base, but then widening to about 0.60 mm width at the base, producing a slightly bulbous basal region. Edge costae of uniform width, about 0.40 mm. Intercostal grooves deep, about 0.22 mm wide. Vertical faces of costae in region adjacent to calice and base, and entire length of principal costae an the costae that flank principal costae, are finely ridged or fluted, such that about 10 carinae occur every mm. Septa hexamerally arranged in 3 cycles (24 septa) according to the formula: S1–2>S3, but the 4 S2 adjacent to the principal S1 are somewhat smaller than those occurring in the lateral systems. S1–2 about 1 mm exsert and have vertical axial edges that bear small teeth that project horizontally into the fossa. S3 about 0.5 mm exsert, but are essentially vestigial inside the calice. Fossa quite deep, containing a small, deep-set, lamellar columella .

Remarks. This species is redescribed based on a reexamination of the holotype. It is unique, in that it is known from only one specimen and is quite unlike any of the other nine Recent species belonging to the nominate subgenus of Sphenotrochus . It differs from other species by having a full corallum shape with a relatively high GCD:LCD, a bulbous base, fluted costal edges, and a deeply-set columella. Given the large amount of collecting in the Sydney region since 1878, even though this species is relatively small, it is surprising that it has not been re-collected.