Pentaceraster alveolatus (Perrier 1875)

Mah, Christopher L., 2023, A new species of Astrosarkus from Western Australia including new Mesophotic occurrences of Indian Ocean Oreasteridae (Valvatida, Asteroidea), Memoirs of Museum Victoria 82, pp. 143-165 : 157

Pentaceraster alveolatus (Perrier 1875)

Figure 9a–f

Pentaceros Perrier 1875: 243 (1876: 59); Koehler 1910: 95 Oreaste r Bell 1884: 73; Domantay and Roxas 1938: 212 Pentaceraster Döderlein, 1916: 428 ; Jangoux 1986: 126; Kohtsuka et al. 2020: 58

Diagnosis. Primary circlet and carinal series bearing large, conical spines, dorsolateral armament present primarily on the disk. Superomarginals and inferomarginals with prominent spines. Spination on disk and arms variably absent to abundant with lateral regions on disk and arms. Arms slender and elongate. Based on Marsh and Fromont (2020), Clark and Rowe (1970).

Comments. Pentaceraster alveolatus is a widely occurring and highly variable species, which apparently displays a significant amount of morphological overlap with other Pentaceraster species within its range. Although an identification has been made with the surest possible accounting, boundaries for differing species and variation observed in the specimens themselves present difficulty. Identification was based on the relatively few spines present along dorsal surfaces along the disk and arms, as outlined by Clark and Rowe (1970), but variation is inconsistent with published taxonomic definitions, as are other instances outlined herein. Revision is desirable.

USNM E37286 is most similar to a large specimen (R= 13 cm) figured by Doderlein (1936: Fig. XXV, Figs.2 & 3 ) identified as P. alveolatus , from the Philippines, showing pronounced spination on the lateral sides of the disk but more weakly on the mid to distal arm regions. However, Doderlein (1936) shows a wide range of spine expression for P. alveolatus from the Philippines to southern Japan, including several individuals with much less spinose abactinal surface and starkly different appearance.

USNM E37286 also shows one to few spines on the superomarginal plates of each interradius, which conflicts with the diagnostic keys in Clark and Rowe (1971). This result would suggest Pentaceraster horridus or Pentaceraster tuberculatus . Neither of these species concepts as outlined by Doderlein (1936) appears consistent with USNM E37286.

If correctly identified, USNM E327286 represents the first occurrence of this species from the African coast and one of the few records of this species from the Indian Ocean. Marsh and Fromont (2020) reported one specimen of this species from Western Australia, from 35 m depth. It is possible that this species only occurs at mesophotic depths in the Indian Ocean. If so, the morphology could be phenotypically variable owing to depth or indicative of a cryptic species .

Occurrence. Widely occurring throughout the Indo-Pacific. Southern Japan, China, Guam, New Caledonia,Samoa, Indonesia, Philippines, Western Australia (single occurrence), 1–54 m.

Range & depth extension. Somalia, 60–70 m.

Material examined. USNM E37286 SW of Gas Jinnah, Somalia, Indian Ocean. 9.68° N, 51.05° E, 60– 70 m. Coll . R / V Anton Bruun , 16 Dec. 1964. 1 dry spec . R=12.1, r=3.9.

Figures

Figure 2. Astrosarkus idipi. Maldives/Mayotte. a, Astrosarkus idipi (white/red form) from Mayotte, 75 m. Photo courtesy Thierry Mayotte; b, Astrosarkus idipi (white/red form) from Maldives. Photo courtesy Paris Stefanopoulis; c, Astrosarkus idipi (orange form) from St. Leu, Reunion Island. Photo by Patrick Plantard; d, Orange form with white highlights from Lifou Island, New Caledonia. Photo courtesy Laurent Ballesta.

Figure 3. Astrosarkus spp. from Australia. a, Astrosarkus sp. Northern Depths, Great Barrier Reef; b, Astrosarkus idipi from Coral Sea Marine Park. Distance between lasers is 10.0 cm.

Figure 9. Pentaceraster alveolatus USNM E37286 a, Abactinal view. Scale bar=2.0 cm; b, Abactinal-lateral view showing degree of spination along arm. Scale bar=0.5 cm; c, Abactinal-lateral view showing spination and superomarginal surface. Scale bar=0.5 cm; d, Actinal-lateral view showing marginal spination. Scale bar=0.5 cm; e, Actinal view. Scale bar=2.0 cm; f, Closeup of oral region and ambulacral spination. Scale bar=0.5 cm.