Asteronyx luzonicus Döderlein, 1927

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 : 14-18

Asteronyx luzonicus Döderlein, 1927

Figs 4–6

Asteronyx luzonicus Döderlein, 1927: 64 , pl. 7 figs 4–5, 6a–d.

Asteronyx luzonicus – Baker et al. 2018: 7–8 , figs 4–5.

Material examined

CHINA • 1 spec.; South China Sea, SE of Hainan Island , seamount; 18°31.76′ N, 112°40.56′ E; depth 1167 m; 27 Jun. 2019; collection event: stn SC002; MSV Shenhaiyongshi leg.; preserved in -80°C; GenBank: MZ 198757 , MZ 203265 ; IDSSE EEB-SW0003 • 1 spec.; same collection data as for preceding; depth 1162 m; 8 Jul. 2019; collection event: stn SC002; MSV Shenhaiyongshi leg.; preserved in -80°C; IDSSE EEB-SW0032 .

Description ( IDSSE EEB-SW 0003)

MEASUREMENTS. Disc diameter 13.5 mm.

DiSC. Flat, pentagonal. Entire dorsal disc covered by smooth, transparent, naked skin, but some small calcified scales between radial shields. Skin on center of dorsal disc becoming mesh-like and less smooth than at periphery of disc. Radial shields narrow, elongate, separate, covered by skin and extending to near disc center, but not meeting in center ( Fig. 4A ). Ventral (oral) surface of disc also covered by smooth skin ( Fig. 4B ). Oral shields slightly triangular. Adoral shield large, wider than long and slightly concave at distal margin, bordering proximal end of a depressed area near genital slit. Two tooth papillae, large and pointed, three smaller pointed lateral oral papillae, teeth also pointed. Two small, short, well separated genital slits in each ventral interradius ( Fig. 4C–D ).

ARMS. Simple, similar in size and length, five in number, with no abrupt change in width proximally, gradually tapering toward arm tip. No dorsal arm plates, arm covered with smooth translucent skin, leaving vertebrae visible ( Fig. 4E ). Ventral and lateral arm plates concealed by thick skin but slightly visible on proximal arm ( Fig. 4F ). Lateral arm plates meet at ventral midline, spines at ventrolateral margin extending onto ventral surface ( Figs 4F–G , 5A–B ). Starting from first free arm segment beyond disc, first two to three arm segments without spines at tentacle pores ( Fig. 4B–C ); third to fourth arm segments with one or two short arm spines, becoming hook-shaped or with one secondary tooth ( Fig. 4C ). Following tentacle pores with two to five hook-shaped arm spines and only uppermost arm spine elongated to simple hook shape, but ventralmost spines with one secondary tooth ( Fig. 5D ). Length of all arm spines decreasing to approximately half length of corresponding arm segment in middle of arm. On distal third of arm, arm spines half as long as corresponding arm segment and transforming into hooks without secondary tooth, except ventralmost arm spine. Ventralmost arm spine becoming cylindrical, blunt with thorny tip, as long as one arm segment ( Fig. 5A–F ). Tube foot elongate, cylindrical, slender, as long as an arm segment and positioned close to ventralmost arm spine ( Fig. 5A–C ).

COLOR. Dorsal disc light brown in center, naked skin between radial shields darker, radial shields whitish brown; ventral interradial areas light brown; arms whitish brown above and below ( Fig. 4 ).

OSSiCLE MORPHOLOGY. Lateral arm plate curved around vertebrae, bearing five spine articulations, each with small muscle opening, but lacking a separate nerve opening ( Fig. 6A–C ). Arm spine articulations at distal edge of lateral plate, raised outwards, pointing distalwards. A depression on inner side of lateral arm plate ( Fig. 6B ). Vertebrae with streptospondylous articulation, ventral side with a longitudinal groove along midline and no oral bridge ( Fig. 6D–H ).

Remarks

The here examined specimens were collected on a deep-sea seamount, attached to a gorgonian. Asteronyx luzonicus was first described by Döderlein (1927) from the Philippines. However, there are few published descriptions of A. luzonicus ( Baker et al. 2018) and the species has not been imaged well before. Döderlein (1927) mentioned an elongated, slender ventralmost arm spine, as long as an arm segment, parallel to the longitudinal arm axis, as a distinguishing morphological feature of A. luzonicus , because in other species of Asteronyx , the ventralmost spine is usually placed transversally to the longitudinal axis of the arm and often reaches twice the length of an arm segment. Dried specimens of A. luzonicus are particularly strikingly dark and a main distinguishing morphological feature of A. luzonicus is the presence of black spots on the disc of sexually mature specimens ( Baker et al. 2018). Specimens from our collection were not sexually mature and only had darker skin on both the dorsal and ventral disc, but they concur with a Baker et al. (2018) in the calcified scales.

Recent studies on species of Asteronyx suggested that features of the dorsal disc surface, as well as the position and length of the genital slit may be important characters to distinguish the six species in this genus (Okanishi et al. 2018). Döderlein did not describe the dorsal disc surface and mentioned few morphological characters to distinguish his new species from other species in the genus Asteronyx , i.e., in characters of the tentacle scale and darker disc spots in sexually mature specimens. Specimens of Asteronyx in our collection are immature but similar in size. Therefore, a comprehensive morphological analysis can be used to distinguish A. loveni from A. luzonicus such as: hook-shaped arm spines with at most one secondary tooth along the arm in A. luzonicus , whereas A. loveni has hook-shaped arm spines with more than one secondary tooth ( Figs 2F , 4F , 5 ); in A. luzonicus the dorsal disc surface is flatter than in A. loveni and becoming rough, mesh-like in the center ( Figs 2A , 4A ); the first two to three arm segments in A. luzonicus have only a tentacle foot and no arm spine, but in A. loveni only the first arm segment is without a single spine ( Figs 2B , 4B ). The ventralmost arm spine is as long as one arm segment, cylindrical, tapered, with a blunt, thorny tip ( Fig. 5H–J ). Asteronyx reticulata Okanishi, Martynov & Fujita, 2018 is similar to A. luzonicus , but differs in having mesh-like skin on its ventral disc (Okanishi et al. 2018).

Distribution

109–2963 m depth. South China Sea, Sibuyan Sea, Samar Sea, Bohol Sea, East China Sea, Andaman Sea, Southern Mozambique ( Baker et al. 2018).

Family Euryalidae Gray, 1840

Genus Asteroschema Örsted & Lütken in Lütken, 1856

Figures

Fig. 4. Asteronyx luzonicus Döderlein, 1927 (IDSSE EEB-SW0003). A. Dorsal disc. B. Ventral disc. C. Ventral arm base (start of first arm spine highlighted). D. Oral frame. E. Dorsal arm. F–G. Ventral arm (proximal and distal region). Abbreviations: ars = arm spine; as = adoral shield; cs = calcified scales; gs = genital slit; tp = tentacle pore. Scale bars: A–B = 2 mm; C–E, G = 1 mm; F = 500 µm.

Fig. 5. Asteronyx luzonicus Döderlein, 1927 (IDSSE EEB-SW0003). A–F. Various shapes of arm spines along the arm. Abbreviations: ars = arm spine; las = lowermost arm spine; st = secondary tooth; tf = tube foot. Scale bars: A = 500 µm; B–F = 200 µm.

Fig. 6. Asteronyx luzonicus Döderlein, 1927, SEM (IDSSE EEB-SW0003). A–C. Lateral arm plates (internal, external). D–H. Vertebrae. D. Proximal view. E. Distal view. F. Ventral view. G. Dorsal view. H. Lateral view. Abbreviations: asa = arm spine articulation; D = dorsal; d = depression; Dist = distal; mo = muscle opening; Prox = proximal; V = ventral. Scale bars: A–B = 300 µm; C = 200 µm; D, G–H = 500 µm; E–F = 800 µm.

Fig. 2. Asteronyx loveni Müller & Troschel, 1842 (IDSSE EEB-SW0002). A. Dorsal disc. B. Ventral disc. C. Oral frame. D. Genital slit. E. Dorsal arm. F. Arm spines. Abbreviations: ars = arm spines; gs = genital slit; rs = radial shield; tp = tentacle pore. Scale bars: A–B = 2 mm; C–E = 1 mm; F = 200 µm.