Ophiactidae Matsumoto, 1915

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 : 46-47

Family Ophiactidae Matsumoto, 1915

Type genus

Ophiactis Lütken, 1856 .

Other genera

Hemipholis Lyman, 1865 .

Description

ARM.Arm shape unbranched; length 3– 4× disc diameter, or length more than 4× 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 in shape. Arm spine cross section round. The ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.6–0.9, or 0.9–1. Arm spines pointed; mainly lateral; predominantly erect, standing perpendicular to arm axis. Longest arm spines between half and one segment long, or 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; cross section oval. Position of lateral arm plate (LAP) arched (wrapped around the arm). Dorsal and/or ventral edge(s) of LAPs without constriction. Ventral position of LAP projecting ventro-proximalwards. Ventro-distal tip of LAP not projecting ventralwards. Arm spine articulation with dorsal and ventral lobes; without sigmoidal fold; arranged over entire distal LAP edge; larger in middle of arm. Distance between spine articulations dorsalwards increasing. Nerve and muscle openings separated by small ridge if at all. Nerve opening approximately as large as muscle opening.

DORSAL DISC. Disc pentagonal or circular; high (above arm level). Integument not obscuring plates. Dorsal disc without granules; with obvious primary plates; with scales; with spines. Dorsal disc scale/plate without tubercles. Radial shield present; without granules/spines; length more than half of the disc radius; scalene (oblique) triangular.

VENTRAL DISC. Gonads restricted to the disc. Ventral interradii without granules/spines. Scales on ventral interradii covering the whole area of an interradius. The number of scales on H line of an interradius about 14–21. Ventral teeth single. Infradental papillae on oral plate present. Buccal scales on OP present. Accessory oral papillae on OP absent. Lateral oral papillae on OP absent. Adoral shield spine present. Lyman’s ossicle present. Oral shield covering less than one third of interradius; much longer than wide or about as long as wide. Madreporite one; with one pore. Adoral shield meeting in front of the oral shield. 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 of equal width all over, or dorsal half widest; entire (single plate). Dental sockets slit-shaped; equal to or more than 50% of the width. At least one socket on DP as perforation with septum. Teeth block-like (with square tip). Teeth on DP arranged as single row.

VERTEBRAE. Vertebrae zygospondylous; beyond segment 5 with short keel; without oral bridge.