Asteronychidae Ljungman, 1867

Goharimanesh, Mona, Stöhr, Sabine, Mirshamsi, Omid, Ghassemzadeh, Fereshteh & Adriaens, Dominique, 2021, Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions, European Journal of Taxonomy 766 (1), pp. 1-63 : 19-20

Family Asteronychidae Ljungman, 1867

Type genus

Asteronyx Müller & Troschel, 1842

Other genera

Astrodia Verrill, 1899 ; Astronebris Downey, 1967 ; Ophioschiza H.L. Clark, 1911 .

Description

ARM.Arm shape unbranched;length more than4× disc diameter; covering without granules/spines/tubercles. Arm combs absent. Dorsal arm plate absent.Accessory dorsal arm plate absent. Ventral arm plate present. Accessory ventral arm plate absent. Girdle of tiny hooks on the arms absent. Spines not all similar in shape ( Fig. 2F–H ). The atypical spines are hook-shaped ( Fig. 2G ). Arm spine cross section round. The ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.2–0.6. Arm spines tapering (conical); at proximal segments only on ventral side of arms; predominantly erect, standing perpendicular to arm axis. Longest arm spines shorter than half a segment. Tentacle scales absent. Position of lateral arm plate (LAP) only lateral ( Fig. 3J–K ). Dorsal and/or ventral edge(s) of LAPs without constriction. Ventral position of LAP not projecting ventro-proximalwards. Ventro-distal tip of LAP not projecting ventralwards ( Fig. 2L ). Arm spine articulation without dorsal and ventral lobes; arranged over entire distal LAP edge; all similar. Distance between spine articulations ventralwards increasing. Nerve and muscle openings separated by large, prominent ridge or regular stereom. Nerve opening smaller than muscle opening.

DORSAL DISC. Disc pentagonal to circular; high (above arm level). Integument obscuring plates. Dorsal disc without granules; with concealed primary plates; without scales ( A. loveni Müller & Troschel, 1842 ) or a few ( O’Hara et al. 2018); without spines. Dorsal disc scale/plate without tubercles. Radial shield present; without granules/spines; length more than half of the disc radius; bar-like.

VENTRAL DISC. Gonads restricted to the disc. Ventral interradii without granules/spines. Scales on ventral interradii absent. Ventral teeth several (tooth papillae). Infradental papillae on oral plate absent. Buccal scales on OP absent. Accessory oral papillae on OP present. Lateral oral papillae on OP absent. Adoral shield spine absent. Lyman’s ossicle absent. Oral shield covering less than one third of interradius; about as long as wide. Madreporite one; with numerous pores. Adoral shield meeting in front of the oral shield. Abradial genital plate not twisted. Number of genital slits one per bursa. Genital slit shorter than half interradius. Genital papillae absent. Dental plate of equal width all over; entire (single plate). Dental sockets slit-shaped to circular; less than 50% of the width. At least one socket on DP as depression or perforation without septum. Teeth spine-shaped. Teeth on DP arranged as covering the entire dental plate evenly.

VERTEBRAE. Vertebrae hourglass-shaped (streptospondylous); beyond segment 5 with short keel ( Fig. 3C, E ); without oral bridge.

Figures

Fig. 2. SEM images of various brittle star ossicles. A–E. Disc structures.A. Dorsal disc, radial shield with tubercles (Ophiomusa lymani (Wyville-Thomson, 1873)). B. Dorsal disc (Ophiolimna bairdi (Lyman, 1883)). C. Ventral disc (Ophionereis porrecta Lyman, 1860), the interradius is assumed as a triangle and H gives its height. D. Dorsal disc, triangular radial shield (Ophiactis savignyi (Müller & Troschel, 1842)). E. Ventral disc, mouth (Ophioderma sp.). – F–H. Atypical arm spines. F. Umbrella-shaped arm spine (Ophiotholia spathifer (Lyman, 1879)). G. Hook-shaped arm spine (Asteronyx loveni Müller & Troschel, 1842).H. Bristle spines (Ophiernus vallincola Lyman, 1878). – I–L. Lateral arm plates (LAP). I. LAP with constriction (Ophioscolex glacialis Müller & Troschel, 1842). J. Dorsal and ventral part of LAP without constriction (Ophiura ophiura (Linneaus, 1758)). K. Ventral part of LAP projecting ventro-proximalwards (Ophiopallas paradoxa Koehler, 1904). L. Ventral part of LAP not projecting ventro-proximalwards (Ophiosphalma fimbriatum (Koehler, 1922)).

Fig. 3. SEM images of various ossicle structures in brittle stars. A. Muscle and nerve opening on LAP separated by small ridge if at all (Amphiura chiajei Forbes, 1843). B. Muscle and nerve opening on LAP separated by large, prominent ridge or regular stereom (Ophiolycus purpureus (Düben & Koren, 1846)). C. Non-keeled vertebra (Amphiura chiajei). D. Keeled vertebra (Ophiothrix fragilis Abildgaard, 1789). E. Vertebra with oral bridge (Euryale aspera Lamarck, 1816). F. Sockets indicate teeth and tooth papillae on dental plate as single row (Amphilepis norvegica (Ljungman, 1865)). G. ½ single row of teeth and ½ tooth papillae (Ophiothrix fragilis). H. ⅔ single row of teeth and ⅓ tooth papillae (Ophiocamax vitrea Lyman, 1878). I. Sockets on dental plate covering evenly (Asteronyx loveni Müller & Troschel, 1842). J–K. LAP not arched = position lateral. L. LAP arched = wrapped around the arm.