Sibogaster nieseni Mah, 2016

Mah, Christopher L., 2025, New Australian deep-sea Goniasteridae (Asteroidea; Valvatacea), Memoirs of Museum Victoria 84, pp. 49-88 : 83-85

Sibogaster nieseni Mah, 2016 .

Figures 17A–D

Sibogaster nieseni Mah, 2016: 136 , Figs. 10A–E.

Material Examined. Indian Ocean. Western Australia. WAM Z100738 . Ningaloo , Western Australia. 22º 15' 59" S, 113º 0' 39" E, 2105.5 m. Coll. Wilson N, Rouse, G., Kirkendale, L., Ritchie, J. aboard RV Falkor March 2020. 1 wet spec. R = 6.7 r = 3.0.

WAM Z100641 . Ningaloo, Western Australia. 21º 53' 9" S, 113º 0' -48" E, 2519.9 m. Coll . Wilson N, Rouse, G., Kirkendale, L., Ritchie, J. aboard RV Falkor March 2020. 1 wet spec . R = 4.5 r = 2.5

WAM Z110291 . Gascoyne Marine Reserve , 22º 16' 11.6832" S, 112º 57' 46.2672" E, 2073 m. Coll. Alvarez, B., Naughton, K.M., Moore, K., Unteidt, C. CSIRO, barcode 10059270, 25 November 2022, 1 wet spec . R = 4.0 r = 1.6.

WAM Z110110 . Site 009, Gascoyne Marine Preserve , ca 113 km WNW of Ningaloo Reef, Western Australia, 22º 14' 22.9344" S, 112º 36' 56. 3976" S, 3747 m. Coll. J. Keesing, et al . CSIRO aboard RV Investigator , barcode 10052707, 26 November 2022. 1 wet spec . R = 5.4 r = 2.2

NMV F241948 , Off Fraser Island , Queensland, Australia. - 25° 19' 31.0794" N, 154° 4' 4.8" E, 2342–2350 m. Coll . T. O’ Hara et al. INV2017 _ V03 , abyss Marine Invertebrates team, 6 Nov 2017, 1 wet spec . R = 3.8 r = 1.6

NMV F307918 . Santa Ridge , Cocos (Keeling) Islands, Indian Ocean, Australia, 13º 33' 42" S, - 13º 33' 10" S, 96º 22 06" E - 96º 22' 56" E, 2418– 2156 m. Coll. by T. O’ Hara , 22 November 2022, 1 wet spec . R = 2.1 r = 0.9.

NMV F307968 . Balthazar Seamount , Christmas Island, Indian Ocean, 11º 21' 33" S 11º 22' 16" S, to 104º 02' 53" S, 104º 3' 28" E, 3510–3611 m. Coll. by T. O’ Hara , 7 October 2022. 1 wet spec . R = 5.4 r = 2.3.

NMV F307970 . Balthazar Seamount , Christmas Island Territory , Indian Ocean, Australia. 11º 21' 33" S to 11º 22' 16" S, 104º 02' 53" E, 3611– 3510 m Coll. by T. O’ Hara , 22 November 2022, 1 wet spec . R = 6.4 r = 2.6.

NMV F307971 . Balthazar Seamount , Christmas Island Territory, Indian Ocean, Australia. 11º 21' 33" S to 11º 22' 16" S, 104 02' 53" E, 3611– 3610m, 1 wet spec . R = 5.3 r = 2.1.

NMV F 307972 . Balthazar Seamount , Christmas Island, Indian Ocean, 11º 21' 33" S, 11º 22' 16" S, to 104º 02' 53" S 104º 3' 28" E, 3611– 3610 m. Coll . T. O’ Hara , 7 Oct 2022. 1 wet spec . R = 3.4 r = 1.1.

Diagnosis. Body stellate (R/r = 3.1 to 6.4). Abactinal plates polygonal in shape, flat, smooth, glassy tubercles absent. Superomarginal plate surfaces smooth to rough, bare, lacking granules. Inferomarginal and actinal plates covered by granules. Paddle-like pedicellariae present. Furrow spines 6 to 10.

Comments. Sibogaster nieseni is a widely occurring species recorded from the Pacific, Atlantic, and now the Indian Ocean, observed between 2000 and 5000 m depths. Figure 17A shows an in situ image of a specimen (WAM Z 100738) of this species off Ningaloo at 2105.5 m on a soft-sediment bottom, which is consistent with other observations of this species. Other observations suggest deposit feeding and predation on sponges (Mah 2024/ 2025 in review).

Description. Body stellate (R/r = 1.88 to 3.0), arms elongate, triangular in shape. Interradial arcs curved to linear.

Abactinal plates round to polygonal, homogenous, flat and variably smooth to rough, with no surficial accessories (no granules, etc.). Each plate periphery surrounded by discrete ring of granules, 20–25, each oval to quadrate in outline. Peripheral granules are large, occupying 25–30% of the total width of each plate, including the peripheral granule. Glassy tubercles absent. Papulae 3–6 per plate present at plate angles.

Marginal plates 24–36 per interradius. Surface of each plate flattened, smooth, flat devoid of surficial accessories. Inferomarginal plates bare on lateral surface adjacent to superomarginals, but actinal surface covered by granules.

Actinal intermediate regions covered by granules, 8–30, hemispherical to pointed. Pedicellariae variably present or absent on abactinal, marginal and actinal plate surfaces. Pedicellariae small (~ 0.25 cm), tong-like with blunt, paddle-like blades, inset into a shallow pit.

Furrow spines 6–10, mostly 7 to 8, quadrate in cross-section with blunt tips. Subambulacral spines 3–5, round to polygonal in cross-section with variable morphology in Atlantic versus Pacific individuals. Adambulacral pedicellariae one or two, elongate, tong-like in shape, thick with complementing valves, taller than furrow spines. Pedicellariae elongate valves, variably present on adambulacral plates sitting adjacent to subambulacral spines, occurring irregularly from the third adambulacral and distally along the furrow series. Oral plates with 8–10 furrow spines.

Variation in Indian Ocean (Western Australian) specimens. WAM Z100738 and WAM Z100641, from the Ningaloo region displays specimens with smooth superomarginals surfaces showing glassy tubercles on the plate surface. Actinal surface covered by rounded granules. Pedicellariae absent from adambulacral plates. Furrow spines 5 to 10 in linear series, space separates from subambulacral accessories in irregular series. Nearest with 3 blunt short spines, covered by 6–8 variably pointed short granules. Others are short, similar to actinal granules with pointed tips.

Occurrence/Distribution. Australia-Indian Ocean. Western Australia, Ningaloo, Gascoyne Marine Preserve, Balthazar Seamount off Christmas Island, off Fraser Island, Queensland. 2106–3747 m

North Pacific. Taney Seamounts B and C, “ NESCA ” Clam sites ( North Pacific ), Patton Seamount and Patton Escarpment , Cascadia Plain , west of Cortez Bank , Hawaiian Islands and Johnston Atoll regions, Musicians Seamount , Japan (2597– 3450 m), Celebes Sea , Indonesia, 2100–4175 m .

East Pacific. Galapagos, 3012 m.

Tropical Atlantic. Off coast of Mauritania, 2114–3162 m