Brisingaster robillardi, : de Loriol, 1883

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 9-12

Brisingaster robillardi deLoriol 1883

Figure 2A–F

Brisingaster robillardi: de Loriol 1883: 55 ; Fisher 1917: 419;1919: 502; 1928: 5, 1940: 205, Spencer & Wright 1966: U78; Clark & Downey, 1992: 464, Mah, 1999: 535; McKnight 2006: 77; Novodinia helenae Rowe 1989: 274 .

Diagnosis. Elongate arms (R/r=approximately 18.7) number 11–12. Skeleton on disk and arms reticulate. Papulae present between reticulate skeletal regions on disk and arm areas. Adambulacral plates vertebrae-shaped but squat with distinct tissue-filled space between plates. Each plate with single adambulacral spine, with variable tips. Adambulacral spines adjacent to mouth and those from midpoint onwards with pointed tip, but those adambulacrals located proximally with wide, club-shaped tips

Comments. Brisingaster robillardi was identified based on the reticulate skeleton and prominent papulae present on the disk and arms, as summarized in Mah (1999). This species was initially described from a single specimen collected in the Indian Ocean near Mauritius (deLoriol 1883). It was subsequently reported by Rowe (1989) but misidentified as Novodinia . Mah (1999) synonymized Novodinia helenae Rowe 1989 with Brisingaster robillardi deLoriol 1883 and re-described this species primarily based on new specimens from Norfolk Ridge and New Caledonia. Mah (1999) noted that Pacific specimens differed from the description of the Indian Ocean material by one character (adambulacral spine tip morphology) and suggested that subsequent evidence could separate the two species from one another. However, further examination of Indian Ocean specimen indicates that both spine types are present in the Pacific and Indian Ocean specimens, suggesting that, at least from morphological evidence there does not appear to be a distinction between the two species.

Morphological variation between the collected individual (USNM 1453671) and other specimens appears to be minimal. For example, the Samoan specimen and those reported by Mah (1998) from New Caledonia, and some Japanese individuals all display 12 arms whereas at least one Japanese specimen (E 7485 in the NMST collection) possessed eleven.

In addition to observations of this species from specimens in Japan (Mah, unpublished data), new observations of this species collected by Okeanos Explorer and specimens present in the MNHN have further identified this species occurrence throughout shallower, deep-sea depths in the central Pacific. ROV observations of this species from Sodwana Bay, South Africa have noted this species in as shallow as 100 m.

Ecological Observations. NOAA ship Okeanos Explorer recorded Brisingaster robillardi from the Marianas region, American Samoa and the central Pacific ( Figs 2A–B ). These individuals were perched on dead coral or sponge stalks, likely climbed to access more optimal water current flow which may have been unavailable closer to the substrate.

As with other observed specimens, especially those from New Caledonia ( Roux 1994), it appears the overall arm length of this species (R/r ratio) is shorter than those in other brisingids, which is consistent with its basal position in the brisingid phylogenetic tree ( Mah 1998) relative to more derived brisingids (e.g., Brisinga , Hymenodiscus , etc.) and freyellids. This suggests that the suspension feeding postures of this species are different from other more derived brisingids which can form a full parabolic fan similar to those in comatulid crinoids. This might also account for the slightly unusual posture of the individuals observed in situ relative to other brisingids observed on stalks. Brisingenes margoae uses its proximally located adambulacral spines to anchor itself to its substratum ( Mah 2016b) and it is possible other brisingids with similar spine morphology do as well.

Indian Ocean specimens of B. robillardi display both the round, club-like adambulacral spine tips ( de Loriol 1883) as well as the bifid spine tips of Rowe (1989). Spine tip variation appears related to distribution along the arm with more proximal adambulacral spines showing the two pronged spines and midpoint to distal spines showing the rounder more clavate tip types.

Occurrence: PACIFIC: Japan (Okinawa region), American Samoa (Tutuila seamount), Central Pacific (Anuu’u seamount), Vanuatu, Fiji Islands, New Caledonia. INDIAN: Western Australia, Mauritius, Madagascar, Sodwana Bay, South Africa, Walters Shoal (southern Indian Ocean). 100-1220m.

Description. Arms elongate, 11–12 (R/r=18.75), disk round, dome-like, interradial arcs acute. Disk and proximal arm region (first 25% of arm length) wider and with proximal inflated arm cavity ( Figs 2A–D ) covered by reticulate plates. Distalmost arms with weakly expressed to absent plates with skin covering ambulacral ossicles extending along remainder of arm length ( Fig. 2E ).

Abactinal plates cover disk and arms with thick, reticulate plates ( Fig. 2D ). Disk with concentric rings of plates including thick plates forming distinct, thick peripheral ring around disk edge with “Y” shaped projection onto proximal arm region ( Fig. 2C–D ). Central disk plates weakly expressed but covered by thick, jagged spines each covered by fleshy, sacculate coverings, each embedded with pedicellariae. Proximal arm region covered by five to six widely separated costate plates with papulae-present in skin between the skeletal ribs ( Fig. 2D ). Two to 30 papulae present per field between arm plates and between disk plates. Along midpoint to distal arm region, costae present every three or four ambulacral ossicles. Large, pointed spines, four to 12 spines per costa on the arms, widely spaced along plates and covered by sacculate sheath. Pedicellariae three-piece, primarily composed of two large valves with large shank-like teeth, valves with 10-15 shorter teeth in 2 to 3 series flanked by two enlarged hooks ( Fig. 2F ). Lateral edges of each valve with three to four evenly spaced shank-like teeth.

Marginal and actinal intermediate plates absent. Post-proximal arm region with widely spaced regular lateral spine arrays, two to three spines every three to four ambulacral plates. Spines larger, more pronounced from midpoint to distal region on arm with larger, more clavate ensacculate sheath forming pronounced teardrop outline around each lateral spine, especially near armtip ( Fig. 2E ).

Adambulacral plates vertebrae-shaped but squat with distinct tissue-filled space between plates. Each plate with single adambulacral spine, tips variable. Adambulacral spines adjacent to mouth and those from midpoint onwards with pointed tip, but those adambulacrals located proximally with wide, club-shaped tips ( Fig. 2F ). Proximal adambulacrals weakly fused (in syzygy, following other brisingid terminology).

The observed specimen was tightly wrapped around a woody stalk, obscuring the oral region an not permitting a clear oral spine count but at least one spine was observed projecting into mouth with two suboral spines present on each oral plate, one enlarged and similar to oral spine and a secondary smaller spine, approximately 10% of height present at base of larger suboral spine.

Based on specimens observed by Okeanos Explorer and from Japanese and South African imagery, this species shows a bright white abactinal disk and arm surface overlying a deep red to orange lateral surface ( Fig. 2A ). Distal ambulacral plates yellow to orange with deep-orange or red lateral surfaces. Lateral spines white to tan.

Material Examined: Pacific. USNM 1453671 , Tutuila Seamount , American Samoa, South Pacific Ocean. -14.316667, -170.65, 257 m, Coll . NOAA ship Okeanos Explorer with ROV D2, EX 1702 ., image: EX1702 _ IMG_20170301 T011018 Z_ ROVHD.jpg. 1 wet spec. R =approximately 15.0, r=0.8. MNHN-IE _2009-2061. W. Epi, Vanuatu. -16.539499; 168.004837, 561-564 m. Coll. N / O Alis, MUSORSTOM 8, CP 1052. 1 wet spec.;MNHN- IE-2013-12872, S Efaté, Vanuatu. -17.879; 168.436. 294-295 m. Coll. Bouchet & Richer de Forges-IRD, N/ O Alis, MUSORSTOM 8, 1 wet spec. MNHN-IE-2013-5133 Between Epi and Tongoa, Vanuatu. 16° -49.62, 168.503, 464-472m, Coll. Bouchet & Richer de Forges-IRD, N/ O Alis, MUSORSTOM 8, CP 1039. 1 wet spec. MNHN-IE- 2013-12873 SE Viti Levu, Fiji Islands. -17.517, 178.64, 244 -252. Coll. Bouchet & Richer de Forges-IRD,N/) Alis, MUSORSTOM 10, CP 1349. 1 wet spec .

Indian Ocean: MNHN-IE-2007-3958, Fort Dauphin region , Southern Madagascar, -25.525, 47.29, 140-144 m. Coll. Nosy B e II, ATIMO VATAE expedition CP 3512. 1 wet spec .

Images Examined

Tutuila seamount, American Samoa, -14.32297358, -170.6478761 , 257.0 m.

EX 1702_IMG_20170301 T 011018Z_ ROVHD.jpg

Aunuu Unit , central Pacific, -14.28145183, -170.5016792, 239 m.

EX 1705_IMG_20170428 T 025627Z_ ROVHD.jpg

BRISINGIDAE

Figures

FIGURE 2. Brisingaster robillardi deLoriol, 1883. A. In situ image of USNM 1453671, American Samoa, 257 m. Scale bar=3.0 mm. B. In situ image from Aunuu Unit, central Pacific, 239 m. Red laser dots = 10 cm distance. USNM 1453671C. Abactinal surface, disk and arms. Scale bar=3.0 mm. D. Costae (skeletal ribs), abactinal surface on arms. Scale bar=3.0 mm. E. Distal surface of arm showing off lateral spines.Scale bar=3.0 mm. F. Furrow spines. Scale bar=1.0 mm. G. SEM of pedicellariae. 850x magnification. Scale bar=20µm.