Astroksarkus idipi Mah 2003

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 : 144-148

Astroksarkus idipi Mah 2003

Figure 1a–e , Figure 2a–d , Figure 3a–b

Mah 2003: 685; Kogure et al., 2009: 73; Wheeler and Pennak, 2013: 94; Conand et al., 2018: 114; Mulochau et al., 2019: 21; Mulochau et al., 2020: 17.

Diagnosis. Body massive, lateral edge rounded, outline weakly stellate, arm tips round. Thorny tubercles absent. Furrow spines 10–11, subambulacral spines 2–5, but only approximately 1.5– 2 times the size of the adjacent furrow spines.

Comments. The collected specimen represents the first individual recovered from the Maldives and the first from the north Indian Ocean. The first such specimen from the Indian Ocean was the paratype from the Indian Ocean ( Mah, 2003). The red/orange and white morphotype in Fig. 1 has been documented from Guam ( Kogure et al., 2009). As summarised herein, this species is widespread throughout the Indo-Pacific, extending from southern Japan, Guam, New Caledonia and northern Australia to the western Indian Ocean ( Mayotte, the Maldives, and Reunion Island). The observed colouration appears variable and may represent infraspecific variation. Further testing for cryptic species is desirable.

Australian individuals (based on video). The Cape York individual (referred to as Cape York video under Videos Referenced) displays a solid red-orange on the abactinal surface with large, mottled white patches along the lateral surface and smaller irregular patches present on each of the convex mounds on the abactinal surface. The video captures only two arms and the lateral surface ( Fig. 3a ).

Body shape stellate, or weakly so. Arms short, but relatively well developed. A species identified by the arms distinctly set off from the disk with the abactinal surface covered by pronounced tumid convexities covered by small, translucent papulae, approximately 500–700 per mound. Singular discrete irregular circular areas possibly pedicellariae, but exact determination is unclear. Ambulacral furrow upturned along arm radius extending to abactinal surface.

The Tegrosse Reef video ( Fig. 3b ) captured a view of the abactinal surface, but with no closeups. Appearance of this specimen was consistent with the description of this species as outlined in the type ( Mah, 2003) with a massive body, short, thick arms with rounded tips and the surface covered by numerous shallow mound-shaped regions, developed in transverse series across the arms.

Colour trends. Colour variation in A. idipi follows two general trends. One color morph is solid orange variably with white highlights and/or mottling on the papular regions, especially on the actinal surface around the mouth. This form has been observed from New Caledonia, Palau, Enewetak, Okinawa, Cape York, and Tegrosse Reef in the Coral Sea, off Queensland, Australia. The second colour form is primarily bright orange or red with bright white papular regions, which are confluent and forming an almost mixed colouration. This latter form has been observed in Guam, Mayotte, Maldives and Reunion Island. Discerning trends with colouration is difficult, given the relatively few observations at hand, but most of the deeper water individuals seem to be the solid-orange colour variant.

Ecological comments. The Cape York , Australia, video observation shows this species in situ on a rocky underhang in close proximity to a cluster of abundant encrusting metazoans, including octocorals, hydroids, sponges and possibly stylasterid corals. While a clear predation event was not evident, it seems likely that one of these types of metazoans is/are a prey item for this species. This would be consistent with an image of Astrosarkus ( Fig. 2b ) with one arm over what appears to be sponges and other encrusting organisms in Mayotte at 91 m.

The specimen from South Diamond Islet/Tegrosse Reef, off Queensland, Australia was observed amidst a mixed field of rhodoliths (unattached algal nodules) and sandy sediment at 151 m. Its coloration, surface texture and absence of apparent spination or tubercles (although closeups were not obtained) suggested that this was A. idipi . Based on the laser scale of 10 cm, this individual was approximately R=20.0, r=15.0 cm, consistent with other occurrences of this species. A small unidentified pufferfish, Canthigaster , was observed adjacent to the animal during the video, but its relationship (which could simply be incidental) to Astrosarkus is unclear.

The individual observed on Lifou Island, New Caledonia (110 m) is consistent with the colour and overall shape ( Mah, 2003) of individuals from Palau and the South Pacific. The degree of arm development seems slightly more pronounced in this individual than in others. This specimen was observed on hard substrate covered by epizoic and encrusting organisms.

Occurrence/distribution. Palau, American Samoa, Southern Japan, Maldives, Mayotte, Reunion Island, 67–210 m

New occurrence. northeastern coast Australia (Queensland), 151 m.

New occurrence. Lifou Island, New Caledonia, 110 m

Specimen referenced. MAL1_330 (unique ID number), Addu , Maldives, 85 m. MAL 1 330, 22/9/2022, site D. 1 wet spec. R =~18.0, r=~12.5

Videos referenced. 1. Tregrosse Reef , South Diamond Islet Australia, - 17.80118148° S, 150.63650088° E, 151 m. Observed by R / V Falkor, ROV SuBastian, dive 365. Video: https://www. youtube.com/watchv=LllPt9v0 URM &list=PLJGVqQI3okzah 21Nq70K57SJs1D54QjkX&index=6&t=22855s

2. Cape York , 500 m-tall detached reef offshore of Cape York, off Queensland, Australia, - 12.39211352° S, 143.85684846° E, 116 m. Observed by RV Falkor voyage FK200930, Northern Depths of the Great Barrier reef, ROV SuBastian, dive S0401. Video: https://www. youtube.com/watch?v=RnUVnNX7yrw&list=PLJGVqQI3okz byfrJeAfGKLJ2SX-3fu4it&index=15&t=5731s

Figures

Figure 1. Astrosarkus idipi Maldives, specimen ID MAL1_330. a, Abactinal surface, specimen showing living coloration. Scale bar=4.0 cm; b, Abactinal surface of arm region. Scale bar=2.0 cm; c, Actinal surface, preserved specimen. Scale bar=4.0 cm; d, Actinal surface, oral region, closeup. Scale bar=1.0 cm; e, Actinal surface, showing furrow, adambulacral plates. Scale bar=2.0 cm.

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.