Acropora (Acropora) rongelapensis, Richards, Zoe T. & Wallace, Carden C., 2004

Richards, Zoe T. & Wallace, Carden C., 2004, Acropora rongelapensis sp. nov., a new species of Acropora from the Marshall Islands (Scleractinia: Astrocoeniina: Acroporidae), Zootaxa 590, pp. 1-5 : 2-5

Acropora (Acropora) rongelapensis sp. nov.

Material examined

Holotype. G 57574 Marshall Islands, Rongelap Atoll lagoon, 11°46.1'N 166°.67.0'E depth 30m, coll. Z. Richards, date 26.VII.2003.

Paratypes. G 57575 Marshall Islands, Rongelap Atoll lagoon, 11°46.1'N 166°67.0'E, depth 32m, coll. Z. Richards, date 26.VII.2003.

G 57576 Marshall Islands, Rongelap Atoll lagoon, 11°46.1'N 166°67.0'E, depth 28m, coll. S. Pinca, date 08.IX.03

Skeletal characteristics (based on holotype)

Corallum. Side attached open branching plate 20 cm max. diameter, with horizontally flattened branches; main branches 4–12 mm wide and up to 100 mm long. Secondary branches up to 45 mm long. Branches round with a flattened base in cross­section, strongly tapered and distal branchlets upcurving.

Corallites. Axial corallites exsert up to 10 mm. Axial corallites outer diameter 1.2– 1.9 mm, inner diameter 0.5–0.8 mm. Calices round, primary septa present up to 2/3 R, a few to all secondary septa present up to ½ R. Radial corallites mixed sizes, not touching, appressed tubular or tubular exsert tending towards immersed or sub­immersed on main branch. Incipient axial corallites difficult to distinguish from tubular radial corallites. Incipient axial corallites and radial corallites occurring laterally along flattened branch tips are tubular. A few exsert tubular corallites are borne along the centre of branches.

Coenosteum

Densely arranged elaborated spinules throughout. Some degree of infilling evident as coenosteum has anamostozed towards branch bases.

Variation Based on Paratypes

Paratype G57576 resembles holotype in all characters except axial corallite diameters are slightly larger (outer diameter 1.9–2.7 mm, inner diameter 0.7–1.0 mm).

Paratype G57575 tends towards an open branching growth form and is apparently from a larger colony than the holotype. Branches are thicker than in the holotype, up to 18 mm diameter, but of similar length. Branches are round or round with a flat base in crosssection. Axial corallites are round and less extended, outer diameter larger than in holotype (1.8–2.9 mm), inner diameter same as in holotype.

Field Characteristics

Small colonies up to 20 cm in diameter, uniform light brown with a whitish glow due to the dense skeleton. Long, bare axial corallites are very prominent. Laterally flattened branches distinguish this species. Occurs subtidally in lagoonal locations. Found at 28–32 m depth.

Remarks

Types of A. rongelapensis show potential for variation in growth ranging from open branching, side­attached plates to open branching arborescent. Variation also exists in axial corallite size, with outer axial corallite diameter ranging from 1.2–2.9 mm and inner diameters range from 0.5–1.0 mm. It is considered that the samples collected thus far are not adequate to represent the full extent of skeletal variation as well as maximum colony size.

Comparisons

We have placed this species in the Acropora loripes group because it is most similar to A. simplex ( Wallace and Wolstenholme, 1998) . However, because of the reduced number of radial corallites and the particularly flattened branches, there is also some similarity to the A. elegans group, and further specimens may indicate a stronger affinity to that group. The molecular material may resolve this issue in the future.