Ophiomoeris petalis, Nethupul & Stöhr & Zhang, 2022

Nethupul, Hasitha, Stöhr, Sabine & Zhang, Haibin, 2022, New species, redescriptions and new records of deep-sea brittle stars (Echinodermata: Ophiuroidea) from the South China Sea, an integrated morphological and molecular approach, European Journal of Taxonomy 810 (1), pp. 1-95 : 61-64

Ophiomoeris petalis sp. nov.

urn:lsid:zoobank.org:act:656A30A3-A81A-4A87-9C19-4007F194788A

Figs 34–35

Diagnosis

Disc with deep interradial incisions with seven lobes and ring of irregular scales bearing a few granules around centrodorsal plate and overlapping with radial shields. Seven thin arms curled under disc.

Etymology

The specific name is derived from the Latin word for flower petals, alluding to the shape of the disc.

Material examined

Holotype

CHINA • South China Sea , SE of Zhongsha Islands, seamount; 13°58.65′ N, 114°52.09′ E; depth 1550 m; 25 Sep. 2020; collection event: stn SC013; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 203278 ; IDSSE EEB-SW0029 .

Paratypes

CHINA • 5 specs; same collection data as for holotype; IDSSE EEB-SW0058 to EEB-SW0062 .

Description (holotype)

MEASUREMENTS. Disc diameter 2.2 mm, heptamerous specimen.

DiSC. Disc heptamerous with deep interradial incisions and a lobe above each arm, four large lobes, three smallest lobes and one intermediate lobe (signs of regeneration after fission). Arms differ in width in groups of 3, 3, 1 arms. Lobes formed by large drop-shaped radial shields, largest one a third of disc diameter in length and two to three times as long as wide ( Fig. 34A–C ). Radial shields distally connected, separated proximally by large triangular scales, covered by small conical granules ( Fig. 34E ). Center of disc sunken and covered by large, round centrodorsal plate without granules ( Fig. 34A, C ). Ring of irregular plates bearing a few conical granules around centrodorsal plate and overlapping with radial shields ( Fig. 34A, C ). Genital slits small, half as long as interradial ventral disc ( Fig. 34F ). Oral shields swollen, much smaller than adoral shields, as wide as long, fan-shaped with pointed proximal angle, slightly concave lateral edges and convex distal edge; size varies among radials ( Fig. 34B, D, F ). Adoral shields swollen, twice as wide as long, with angled, concave proximal edges of oral shield, not separating it from arm ( Fig. 34F ). Jaw as wide as long bearing one pointed ventralmost tooth and three spiniform lateral oral papillae, proximalmost one spine-like, other two shorter and rounded ( Fig. 34F ). All teeth spiniform like ventralmost tooth ( Fig. 35B, D, F ).

ARMS. Seven thin arms, curled under disc. Dorsal arm plates fan-shaped, two times as wide as long, with convex distal edge and always separated ( Fig. 34G ). Ventral arm plate much wider than long on proximal segments, but reduced to small, round, thin scales, embedded in a strand of thick skin running along entire arm distally, always present along arm and always separated ( Fig. 34H ). Four thick, conical, smooth arm spines, two thirds arm segment in length ( Fig. 34D, H ). One minute tentacle scale clearly visible on proximal arm segments ( Fig. 34D ).

COLOR. In alcohol, entire specimen creamy white.

OSSiCLE MORPHOLOGY. Arm spine articulation formed by two thick, smooth, curved lobes, ventral lobe smaller than dorsal lobe, positioned at angle to distal edge of lateral plate, with large muscle opening and small nerve opening, the latter large in dorsalmost articulation. Volute-shape not well defined, absent in dorsalmost articulation, dorsal and ventral articular lobes connected but separating in ventral articulations ( Fig. 35A–C ). Vertebrae elongated, with streptospondylous articulation, dorsal and lateral furrows absent, middle section much lower than proximal part and distal muscle flanges, with straight ambulacral groove. Podial basins at distal end, tongue-like with round hole ( Fig. 35D–F ).

Variations in paratypes

Five heptamerous paratypes, with disc diameter ranging from 1.45 mm to 1.87 mm. All with similar morphological features as holotype, having conical granules on disc plates/scales and large, drop-shaped radial shields. Most paratypes with arms curled under disc.

Remarks

The oral frame arrangement and the lobe-like shape of the disc concur with the genus Ophiomoeris , which was recently transferred to Ophiacanthidae ( O’Hara et al. 2018) . The arm spine articulation of this genus is interpreted as a variation of the volute-shape typical of the family Ophiacanthidae . Previously only four species of Ophiomoeris were recognized and all of them are pentamerous: O. obstricta ( Lyman, 1878) , O. exuta Stöhr, 2011 , O. nodosa ( Koehler, 1905) and O. tenera ( Koehler, 1897) . The seven-fold symmetry is consistent in all our specimens. This is the first record of a sevenarmed (or indeed non-pentamerous) species in the genus Ophiomoeris , and this distinguishes it from all congeners. The size differences among the seven sections of the animals suggests that it is a fissiparous species. Morphological characters to differentiate species in the genus Ophiomoeris are otherwise difficult to interpret due to their high morphological variation among individuals. Taking geographic distribution into account, there may be several cryptic species complexes in the genus Ophiomoeris that can only be resolved by a molecular study ( O’Hara & Stöhr 2006; Stöhr 2011).

Distribution and habitat

South China Sea (1550 m), found on a deep-sea seamount near the Zhongsha Islands.

Order Amphilephidida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017

Suborder Gnathophiurina Matsumoto, 1915

Superfamily Ophiactoidea Ljungman, 1867

Family Ophiactidae Matsumoto, 1915

Genus Ophiactis Lütken, 1856

Figures

Fig. 34. Ophiomoeris petalis sp. nov., holotype (IDSSE EEB-SW0029). A. Dorsal disc. B. Ventral disc. C. Dorsal disc (SEM). D. Ventral disc (SEM). E. Dorsal disc lobe (SEM). F. Oral frame (SEM). G. Dorsal arm. H. Ventral arm. Abbreviations: ars = arm spine; as = adoral shield; dap = dorsal arm plate; gra = granula; gs = genital slit; os = oral shield; ts = tentacle scale; vap = ventral arm plate. Scale bars: A, C = 500 µm; B, G–H = 200 µm; D = 1 mm; E = 250 µm; F = 300 µm.

Fig. 35. Ophiomoeris petalis sp. nov., SEM, paratype (IDSSE EEB-SW0031). A–C. Lateral arm plate. D–F. Vertebrae. D. Dorsolateral view. E. Ventral view. F. Lateral view. Abbreviations: Dist = distal; dl = dorsal lobe; mo = muscle opening; no = nerve opening; Prox = proximal; vl = ventral lobe; vs = volute-shaped. Scale bars: A–B, E = 200 µm; C–D, F = 100 µm.