Ophiohelidae Perrier, 1893

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 : 27

Family Ophiohelidae Perrier, 1893

Type genus

Ophiohelus Lyman, 1880 .

Other genera

Ophiomyces Lyman, 1869 ; Ophiothauma H.L. Clark, 1938 ; Ophiotholia Lyman, 1880 .

Description

ARM. Arm shape unbranched; length 3× disc diameter; covering without granules/spines/tubercles. Arm combs absent. Dorsal arm plate present. Accessory dorsal arm plate absent. Ventral arm plate present. Accessory ventral arm plate absent. Girdle of tiny hooks on the arms absent. Spines all similar ( Ophiomyces ) or not similar in shape. The atypical spines are umbrella-shaped ( Ophiotholia and Ophiohelus ) ( Fig. 2F ). Arm spine cross section round ( Ophiotholia ), or oval ( Ophiomyces ). The ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.2–0.6, or 0.9–1. Arm spines tapering (conical), or flat ( Ophiomyces ), or cylindrical ( Ophiotholia ); mainly lateral; predominantly parallel to arm axis (adpressed). Longest arm spines between one and two segments long. Tentacle scales present; pores visible along most of the arm; slightly longer than wide; shorter than the spine nearby. Position of lateral arm plate (LAP) arched (wrapped around the arm). Dorsal and/or ventral edge(s) of LAPs with constriction ( Ophiotholia ), or without constriction ( Ophiomyces ). Ventral position of LAP projecting ventro-proximalwards. Ventro-distal tip of LAP projecting ventralwards ( Fig. 2K ). Arm spine articulation with dorsal and ventral lobes; without sigmoidal fold; arranged over entire distal LAP edge; ventralwards increasing in size. Distance between spine articulations equal. Nerve and muscle openings separated by small ridge if at all. Nerve opening smaller than muscle opening.

DORSAL DISC. Disc circular; a sac-like shape (much higher than wide). Integument obscuring plates. Dorsal disc without granules; with concealed primary plates; with scales; with spines. Dorsal disc scale/plate without tubercles. Radial shield absent.

VENTRAL DISC. Gonads restricted to the disc. Ventral interradii without granules/spines ( Ophiotholia ), or with spines ( Ophiomyces ). Scales on ventral interradii absent. Ventral teeth several (tooth papillae). Infradental papillae on oral plate present. Buccal scales on OP absent. Accessory oral papillae on OP absent. Lateral oral papillae on OP present; multiple rows of lateral papillae; paddle-shaped. Adoral shield spine absent. Lyman’s ossicle absent. Oral shield covering less than one third of interradius; much longer than wide. Madreporite no data. Adoral shield separated. Abradial genital plate not twisted. Number of genital slits one per bursa. Genital slit longer than half the length of an interradius. Genital papillae absent. Dental plate ventral half widest; entire (single plate). Dental sockets circular; less 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 a single row on ⅔ and a cluster of tooth papillae on ⅓ of dental plate.

VERTEBRAE. Vertebrae zygospondylous; beyond segment 5 with short keel; 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)).