Paracyathus darwinensis, Cairns, 2004

Cairns, S. D., 2004, The Azooxanthellate Scleractinia (Coelenterata: Anthozoa) of Australia, Records of the Australian Museum 56, pp. 259-329 : 282-284

Paracyathus darwinensis n.sp.

Figs. 4A,B

Records/Types. Holotype: 12°27.75'S 130°49.40'E (outside breakwater, Larrakeyah Naval Base), Darwin Harbour, NT (type locality), depth unknown, 20 August 1998, NTM C8139 . Paratypes: 12°29.00'S 130 51.00'E (wreck of “ Zealandia ”), Darwin Harbour, NT, 22 m, 29 July 1994, 5: 3, NTM C7963 and 2, USNM 1008826 ; Kunmunyah BG- 149 , 12°04.98'S 131°08.40'E (east of East Vernon Island ), NT, 26 m, 2, 10 October 1993, NTM C8035 ; Kunmunyah BG-141 , 12°07.02'S 131°07.02'E (northeast of Glyde Park , Vernon Islands), NT, 20 m, 4, 10 October 1993, NTM C8034 ; 12°28.17'S 130°50.51'E (off Pontoon , Stokes Hill Wharf), Darwin, NT, surface, 1 in alcohol 19 February 2002, NTM C8161 ; 12°28.35'S 130°50.57'E ( Iron Ore Wharf ), Darwin Harbour, NT, depth unknown, 1 in alcohol, 16 August 1998, NTM C8143 ; 12°28.29'S 130°50.80'E ( Fort Hill Wharf ) Darwin Harbour, NT, depth unknown, 1 in alcohol, 19 August 1998, NTM C8144 .

Description. Corallum ceratoid, the largest specimen (NTM 8161) 10.9×9.0 mm in CD and 9.5 mm in height, the holotype smaller, measuring 7.4×6.0 mm in CD and 9.0 mm in height. Calice elliptical, the GCD:LCD ranging from 1.07–1.27, younger coralla being more circular, larger more elliptical. Corallum attached by a robust pedicel (PD:GCD = 0.41–0.68), but not approaching subcylindrical. Costae flat to only slightly convex, all equal in width and prominence, all about 0.25 mm wide near calice, and separated by shallow, narrow intercostal striae. Corallum white, except for upper mm of theca and exsert portions of septa, which are light brown to light black in colour, appearing as a band or disconnected band around upper thecal circumference. Axial edges of S1–2 also pigmented the same colour, or, in rare cases, a light blue.

Septa hexamerally arranged in 5 cycles, the last cycle not complete.A complete fourth cycle (48 septa) is achieved at a GCD of 4–5 mm; above this GCD pairs of S5 are progressively inserted, usually in end half-systems, such that the largest specimen of GCD 10.9 mm has 80 septa, or 16 pairs of S5. Septal formula: S1–2>S3>S4>=S5. S1–2 moderately exsert (1.0– 1.3 mm), with straight axial edges, each of which bears a single, slender, vertical paliform lobe, the lobes (P2) associated with the S2 being slightly larger and rising slightly higher in the fossa than those on the S1. S3 slightly less exsert (0.6 mm), about 0.8 width of the S1– 2, each S3 bearing a prominent paliform lobe that rises higher in the fossa than the P1–2 and usually bears 3–4 smaller teeth that are inclined obliquely upward. This axial dentition blends into and is almost indistinguishable from the columellar elements. S4 about 0.5 mm exsert, and at upper thecal edge fuse to their adjacent S1 or S2, thus producing a characteristically jagged, or lancetted, thecal edge. S3 about 0.6 width of an S1–2, each bearing a very small paliform lobe, invariable fused to the adjacent much larger P3. If S5 present in a half-system, they assume the shape of the S4 as just described, and the flanked S4 assumes the shape and paliform lobe of the S3 as described above. Fossa deep, containing a well-developed columella composed of 20–25 slender papillose elements.

Remarks. It may seem inadvisable to describe yet another species of Paracyathus , when there are 17 species known from the Indo-West Pacific, most known only from their type specimens and rather terse descriptions (e.g., Alcock, 1893: northern Indian Ocean; Duncan, 1889: Mergui Archipelago). Nevertheless, P. darwinensis has a combination of characters that allows it to be distinguished from all congenerics previously described, i.e., a distinctive pigmentation of its upper theca and septa and the lancetted thecal edge. To a lesser extent its ceratoid corallum and number of septa are also of use in distinguishing it.

Etymology. Named for the town of Darwin, Australia, the type-locality of the species.

Distribution. Known only from the Darwin region, 0– 26 m.