Aquilonastra aileenae, Kobayashi & Yamamoto & Arai & Woo & Fujita, 2025

Genus Aquilonastra O’Loughlin View in CoL in O’Loughlin and Waters, 2004 Aquilonastra aileenae n. sp. ( Figs 2 View Fig , 3 View Fig )

Material examined. Holotype: USMCRC-Echi 0031 ( R = 8.2 mm, r = 5.8 mm), 20 August 2020, Pantai Pasir Hitam , Langkawi Island, Langkawi Islands, Malaysia, 6°26.007′N, 99°47.773′E ( Fig. 1), at an intertidal depth, fixed in 99% ethanol. GoogleMaps

Paratypes: USMCRC-Echi 0032 ( R = 9.1 mm, r = 6.4 mm), 0033 ( R = 7.7 mm, r = 4.6 mm), 0034 ( R = 6.4 mm, r = 4.5 mm), 0035 ( R = 5.5 mm, r = 3.6 mm), data as for holotype; USMCRC-Echi 0036 ( R = 8.7 mm, r = 6.5 mm), 0037 ( R = 5.6 mm, r = 4.1 mm), 0038 ( R = 3.3 mm, r = 2.9 mm), 2 March 2017, Singa Besar Island , Langkawi Islands, Malaysia, 6°13.548′N, 99°44.603′E, at an intertidal depth, fixed in 99% ethanol GoogleMaps .

Description of holotype. R, 8.2 mm; r, 5.8 mm. Arms five, broadening proximally, gradually tapering toward arm tips, forming broad stellate body ( Fig. 2A, B View Fig ). Abactinal skeleton convex, exhibiting regular close meshwork ( Fig. 2B View Fig ). Each mesh smaller than surrounding abactinal plates, containing one papula ( Fig. 2B, C View Fig ). Papulae absent on interradii and lateral side of arms ( Fig. 2B View Fig ). Abactinal plates ovate or 3–6-lobed, with glassy convexities ( Figs 2D View Fig , 3A View Fig ), regularly arranged in longitudinal and transverse series ( Fig. 2B View Fig ). Carinal abactinal plates distinct, partially imbricated by flanked abactinal plates, regularly arranged in a longitudinal series. Primary radial plates four-lobed, arranged in circular series around anal area ( Fig. 2E View Fig ). Madreporite single, adjacent to two of five primary radial plates. Secondary abactinal plates absent ( Fig. 2B View Fig ). Each abactinal plate bearing 6–14 abactinal spinelets arranged in crescent form rows ( Fig. 2C View Fig ). Abactinal spines 0.03–0.05 mm in length, straight, domed to short conical, distally smoothed or with serration ( Figs 2C View Fig , 3B View Fig ).

Superomarginal plates round to rounded triangular, as large as or slightly larger than adjacent abactinal plates, arranged in regular longitudinal series at abactinolateral portion of arms ( Fig. 2F View Fig ). Inferomarginal plates transversely elongated rectangles with abradially rounded corners, twofold larger than corresponding superomarginal plates, arranged in regular longitudinal series along body fringe. Each supero- and inferomarginal plate bearing 7–13 spinelets and 24–43 spinelets and spines ( Fig. 2G View Fig ), respectively. Supero- and inferomarginal spinelets 0.03–0.04 mm in length, straight, conical, with splayed thorns distally ( Figs 2G View Fig , 3C View Fig ). Two types of inferomarginal spines: on lateral side of plate, 0.11 mm in length, straight, spatulate, distally serrated ( Figs 2G View Fig , 3D View Fig ); on actinal side of plate, same shape as actinal spines.

Actinal plates round to ovoid, arranged in five regular longitudinal series ( Fig. 2H View Fig ). Actinal series extend over half arm length, longest in first series, gradually shortening toward fifth series. Each actinal plate bearing 2–5 actinal spines ( Fig. 2I View Fig ). Actinal spines 0.12–0.15 mm in length, curved, sacciform, conical, distally serrated ( Figs 2I View Fig , 3E View Fig ).

Adambulacral plates transversely elongated, longitudinally constricted at median section of each plate ( Fig. 2H View Fig ). Each adambulacral plate bears 3–7 furrow spines on adradial part of plate and 1–5 subambulacral spines on abradial section ( Fig. 2I View Fig ). Furrow and subambulacral spines each arranged in one curved series, similar shape, 0.19–0.23 mm in length, straight, spatulate, blunt tip ( Figs 2I View Fig , 3F View Fig ).

Ambulacral plates transversely elongated, medially narrowed ( Fig. 2J View Fig ). Adradial triangle part of plate projects proximally, overlapping preceding plate. Superambulacral and superactinal plates bridge corresponding ambulacral/actinal, and actinal/abactinal plates internally. Tube feet with suckered disks, arranged biserially.

Pedicellariae absent.

Gonads attached on abactinal body wall ( Fig. 2J View Fig ). Gonopores unobservable.

Body color mottled brown or olive ( Fig. 2A View Fig ).

Variations in paratypes. Shown in Table 1.

Distribution. Aquilonastra aileenae is documented solely from Pantai Pasir Hitam, Langkawi Island, Malaysia, and Singa Besar Island, Malaysia, under locks in the intertidal zone with living and dead corals.

Etymology. The specific name is dedicated to the honor of Professor Dato’ Dr. Aileen Tan Shau Hwai (CEMACS, Universiti Sains Malaysia) who has contributed significantly to the study of marine invertebrate biodiversity in Malaysia.

Remarks. Eight examined Aquilonastra aileenae specimens exhibit a flat and stellate body, regularly arranged abactinal and actinal plates, a distinct carinal series, glassy convexities on the abactinal plates, and superambulacral and superactinal plates ( Figs 2 View Fig , 3 View Fig ), aligning closely with the diagnosis of the genus Aquilonastra by O’Loughlin and Waters (2004). Out of 33 recognized Aquilonastra species, A. aileenae is most closely related to three western Indian Ocean species, namely A. lorioli (Koehler, 1910) , A. marshae O’Loughlin and Rowe, 2006 , and A. samyni O’Loughlin and Rowe, 2006 , sharing five arms, a single madreporite, gonads attached to the abactinal body wall, and distinctive domed to short conical abactinal spinelets ( O’Loughlin and Rowe 2006). However, the present specimens lacked secondary abactinal plates ( Fig. 2B View Fig ), distinguishing them from the three related species, which possess secondary abactinal plates ( O’Loughlin and Rowe 2006). Additionally, A. aileenae possesses 15–43 superomarginal spinelets and 2–5 actinal spines on each plate ( Table 1), whereas A. lorioli and A. marshae have fewer than 11 superomarginal spinelets and A. samyni has 8–14 actinal spines ( O’Loughlin and Rowe 2006).

All eight A. aileenae specimens possess either five arms or (exceptionally) four arms, a single madreporite, and gonads attached to the abactinal body wall ( Fig. 2A, E, J View Fig ). These morphological characters suggest that this new species is not fissiparous and have pelagic development (refer to Byrne 2006; O’Loughlin and Rowe 2006), distinguishing it from the 11 fissiparous and 3 benthic development species within the genus Aquilonastra ( O’Loughlin and Rowe 2006; O’Loughlin and Bribiesca-Contreras 2015).