Ophiacantha aster, 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 : 57-61

Ophiacantha aster sp. nov.

urn:lsid:zoobank.org:act:6AB8A891-700D-4BF2-8873-5CD18178795E

Figs 31–33

Diagnosis

Disc slightly pentagonal, interradially excavated and covered by conical pointed granules with wide, round base. Single small, broad, triangular, pointed tentacle scale. Adoral shields larger than oral shield. Jaw with one large, blunt, wide ventralmost tooth and four to five lateral oral papillae. Top of radial shields and center of disc creamy white, dark brown lines radiate from disc center to arms.

Etymology

The specific name is derived from the Greek word for ‘star’, alluding to the shape and color of the dorsal disc.

Material examined

Holotype

CHINA • South China Sea , SE of Zhongsha Islands, seamount; 13°59.70′ N, 115°24.81′ E; depth 516 m; 20 Sep. 2020; collection event: stn SC011; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 203275 ; IDSSE EEB-SW0026 .

Paratypes

CHINA • 1 spec.; same collection data as for holotype; GenBank : MZ 203276 ; IDSSE EEB-SW0027 • 12 specs; same collection data as for holotype; IDSSE EEB-SW0046 to EEB-SW0057 .

Description (holotype)

MEASUREMENTS. Disc diameter 8.5 mm.

DiSC. Disc slightly pentagonal, interradially excavated, covered by oval disc scales, each bearing a conical pointed granule with wide, round base ( Fig. 31A–B ). At disc periphery and lateral disc, granules lower and less pointed, near oral shields no granules on scales ( Fig. 31C–F ). In disc center, granules spine-like ( Fig. 31C ). Ventral disc reduced to oral frame ( Fig. 31B ). Radial shields long, narrow, parallel to each other, but well separated, distal ends exposed ( Fig. 31A, E ). Genital slits conspicuous, short, extending from oral shield to periphery of disc ( Fig. 31E ). Oral shield broadly triangular, with acute proximal angle, with straight, convex or wavy distal edge. Adoral shields larger than oral shield, trapezoid extending along concave proximal edges of oral shield, not separating it from arm ( Fig. 31F ). Jaw with one large, blunt, wide ventralmost tooth, four to five lateral oral papillae, first three elongated, spiniform, first possibly infradental papilla, distal two papillae larger, distalmost one scale-like (possibly adoral shield spine) ( Fig. 31F ). Dorsal teeth square, with straight proximal edge ( Fig. 31F ).

ARMS. Moniliform. Dorsal arm plates fan-shaped, distal edge convex, acute proximal angle, straight to slightly concave proximolateral edges, completely separated ( Fig. 31G ). Ventral arm plates pentagonal to broadly rectangular, wider than long, concave lateral edges around tentacle pore, distal edge straight with small inward curve, separated ( Fig. 31H ). Lateral arm plates with a high spine-bearing ridge, meeting dorsally and ventrally ( Fig. 31I–K ). Eight transparent, rounded arm spines, more or less thorny ( Fig. 31J–K ). Four dorsalmost spines longest, with rough surface, as long as three arm segments, meeting at dorsal midline, length gradually decreasing ventralwards. Ventral arm spines tapering, rougher than dorsal arm spines, one to two arm segments in length ( Fig. 31I–K ). Tentacle pore on proximalmost and second arm segments half to two-thirds arm segment in length ( Fig. 31B ). One to three arm segments covered by disc and only possessing ventral arm spines ( Fig. 31I ). Arm spines on fourth to sixth arm segments longer than those on middle or dorsal arm segments ( Fig. 31I–J ). Arm spines on first six arm

segments tapered, smooth, but distal to sixth segment spines rough or thorny ( Fig. 31K ). One small, broad, triangular, pointed tentacle scale, one third as long as ventral arm plate ( Fig. 31B ).

COLOR. Top of radial shields and center of disc creamy white, but dark brown lines radiate from disc center to arms, outside radial shields, a third line between each pair of radial shields continues along center of each arm. Similar longitudinal, lighter brown line on ventral arms ( Fig. 31 ).

OSSiCLE MORPHOLOGY. Proximal lateral arm plate short, strongly curved and arm spine articulations well developed, with large muscle opening and small nerve opening ( Fig. 32A ). Spine articulations volute-shaped perforated lobe ( Fig. 32A–B ). Arm spines with sparse thorns ( Fig. 32C ). Vertebrae

with a short streptospondylous articulation, as wide as long, proximal end with podial basins. Dorsal end of vertebrae distally triangular, proximally slightly curved inwards, with shallow dorsal furrow ( Fig. 32D–H ). Ambulacral groove without oral bridge ( Fig. 32F–G ).

Variations in paratypes

Paratypes generally similar to holotype, disc diameters 3.9–9.0 mm, but some morphological variations were observed. Only dorsal arm spines tapered or thorny in some specimens ( Fig. 33 ). One paratype had black dots scattered near periphery of disc ( Fig. 33A ). Disc color of some paratypes slightly lighter than in holotype and interradials not as strongly excavated as in holotype, radial shields more widely separated ( Fig. 33B ). Smallest paratype with 3.9 mm disc diameter and similar to holotype, except fifth arm segments with thorny spines. Lateral oral papillae four to six, distalmost one varies from scalelike, flat to narrower and pointed, ventralmost tooth much larger than oral papillae ( Fig. 33C–D ). Disc granules varied in shape; some specimens with taller spines in disc center ( Fig. 33E ).

Remarks

The arm spine articulation is here interpreted as a variation of the zygospondylous type, not uncommon in the family Ophiacanthidae , typical of epizoic species. The deeply interradially excavated disc is a character used by Paterson (1985) to distinguish the no longer valid subfamily Ophioplinthacinae Paterson, 1985 ( Martynov 2010), but the narrow, long radial shields and the oral frame fit with the genus Ophiacantha . Ophiacantha aster sp. nov. differs from most species of the genus by having deep incisions in the disc along with five (more or less) lateral oral papillae. Ophiacantha antarctica Koehler, 1900 resembles O. aster sp. nov. by having long narrow radial shields with a more or less excavated interradial disc, four elongated lateral oral papillae and tapering long uppermost arm spines, but it differs in having a thickened integument that covers the disc scales, conical granules on the scales with two to five fine spinules, and near the periphery of the disc the granules are less elongated and more cylindrical. Ophiacantha antarctica has seven arm spines with a thin pointed tip ( Koehler 1900), frequently has disc spines on the dorsal arm plates and transversely split dorsal arm plates dividing them into a small proximal and larger distal section (observation from anonymous reviewer).

Another species that resembles Ophiacantha aster sp. nov. is O. veterna Koehler, 1907 , known from the Atlantic Ocean (2200 m), which has similar morphological characteristics in its disc shape, oral shield, adoral shield, oral papillae and arm spines, but differs mainly in having dense small granules on both ventral and dorsal disc and in the shape of the ventral arm plate along the arm ( Koehler 1907 a). The new species is unusually colorful among deep-water species.

Distribution and habitat

Found on a seamount near the Zhongsha Islands, South China Sea (516 m) as a colony attached to a dead coral branch. The vertebrae of Ophiacantha aster sp. nov. are almost streptospondylous and suggest an epizoic life-style, typical of suspension feeders.

Figures

Fig. 31. Ophiacantha aster sp. nov., holotype (IDSSE EEB-SW0026). A. Dorsal disc. B. Ventral disc. C. Center of disc (elongated conical granules highlighted). D. Distal edges of radial shield. E. Lateral disc. F. Oral frame. G. Dorsal arm. H. Ventral arm. I–K. Lateral arm. Abbreviations: as = adoral shield; dap = dorsal arm plate; das = dorsal arm spine; gra = granule; gs = genital slit; lap = lateral arm plate; os = oral shield; rs = radial shield; ts = tentacle scale; vap = ventral arm plate; vas = ventral arm spine. Scale bars: A–B, G–K = 1 mm; C–F = 500 µm.

Fig. 32. Ophiacantha aster sp. nov., SEM, paratype (IDSSE EEB-SW0027). A–B. Lateral arm plate. C. Base of dorsal arm spine. D–H. Vertebrae. D. Proximal view. E. Distal view. F. Ventral view. G. Dorsal view. H. Lateral view (broken distal end). Abbreviations: asa = arm spine articulation; D = dorsal; Dist = distal; dl = dorsal lobe; mo = muscle opening; no = nerve opening; Prox = proximal; V = ventral; vl = ventral lobe; vs = volute-shaped. Scale bars: A–D, F–H = 500 µm; E = 300 µm.

Fig. 33. Ophiacantha aster sp. nov., paratypes. A–B. Dorsal disc. C–D. Ventral disc. E. Center of disc (elongated conical granules highlighted). F. Dorsal arm. G. Ventral arm. Scale bars A, C = 1 mm; B, D, F–G = 2 mm; E = 500 µm.