Euryalidae Gray, 1840

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 : 20-21

Family Euryalidae Gray, 1840

Type genus

Euryale Lamarck, 1816 .

Other genera

Asteromorpha Lütken, 1869 ; Asteroschema Örstedt & Lütken, 1856 ; Asterostegus Mortensen, 1933 ; Astrobrachion Döderlein, 1927 ; Astroceras Lyman, 1879 ; Astrocharis Koehler, 1904 ; Ophiocreas Lyman, 1869 ; Squamophis Okanishi Okanishi, O'Hara & Fujita, 2011 ; Sthenocephalus Koehler, 1898 ; Trichaster Agassiz, 1836 .

Description

ARM. Arm shape branched; length more than 4× disc diameter; covering with granules. Arm combs absent. Dorsal arm plate absent. Accessory dorsal arm plate absent. Ventral arm plate present or absent. Accessory ventral arm plate absent. Girdle of tiny hooks on the arms absent. Spines not all similar in shape.Atypical arm spines are hook-shaped.Arm spine cross section round. The ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.9–1. Arm spines cylindrical; 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 present; pores visible along the arm; nearly as long as wide; shorter than the spine nearby; cross section round. Position of lateral arm plate (LAP) only lateral. Dorsal and/or ventral edge(s) of LAPs without constriction ( Fig. 2J ). Ventral position of LAP not projecting ventro-proximalwards. Ventro-distal tip of LAP not projecting ventralwards. Arm spine articulation without dorsal and ventral lobes; restricted to (the ventral or central) portion of the distal edge; all similar. Distance between spine articulations not applicable (two spine articulation). Nerve and muscle openings separated by large, prominent ridge or regular stereom. Nerve opening approximately as large as muscle opening ( Fig. 3A–B ).

DORSAL DISC. Disc pentagonal; flat (about same level as arms). Integument not obscuring plates. Dorsal disc with granules; with concealed primary plates; without scales; without spines. Dorsal disc scale/plate without tubercles. Radial shield present; with tubercles grown out of plate; length more than half of the disc radius; bar-like.

VENTRAL DISC. Gonads not restricted to the disc (extending into the basal portion of the arms) or restricted to the disc ( Asteroschema ). Ventral interradii without granules/spines. Scales on ventral interradii absent. Ventral teeth single. Infradental papillae on oral plate present. Buccal scales on OP absent. Accessory oral papillae on OP absent. 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 multiple; with one pore, or 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; fragmented. Dental sockets slit-shaped; equal to or more than 50% of the width. At least one socket on DP as depression or perforation without septum. Teeth flat (with round or slightly pointed tip, but never spine-like). Teeth on DP arranged as single row.

VERTEBRAE. Vertebrae hourglass-shaped (streptospondylous); beyond segment 5 non-keeled; with oral bridge ( Fig. 3E ).

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.