Ophiotomidae Paterson 1985

Family Ophiotomidae Paterson, 1985

Ophiotoma Lyman, 1883.

Ophiocomina Koehler in Mortensen, 1920; Ophiocopa Lyman, 1883; Ophiomitra Lyman, 1869; Ophiopristis Verrill, 1899; Ophiotreta Verrill, 1899.

ARM. Arm shape unbranched; length 3–4× 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 oval. The ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.6–0.9 to 0.9–1 (in Ophiocopa more pointed than in Ophiotreta). Arm spines flat; mainly lateral; predominantly erect, standing perpendicular to arm axis. Longest arm spines between one and two segments long, or longer than two segments (Ophiocopa). Tentacle scales present; pores visible along most of the arm; nearly as long as wide (Ophiotreta), or slightly longer than wide (Ophiocomina); 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 not projecting ventro-proximalwards. Ventro-distal tip of LAP not projecting ventralwards.Arm spine articulation with dorsal and ventral lobes; with a fully developed sigmoidal fold; arranged over entire distal LAP edge; dorsalwards increasing in size. Distance between spine articulations dorsalwards increasing. Nerve and muscle openings separated by small ridge if at all. Nerve opening smaller than muscle opening.

DORSAL DISC. Disc circular; high (above arm level). Integument obscuring plates. Dorsal disc with granules; with concealed primary plates; with scales; with spines. Dorsal disc scale/plate without tubercles. Radial shield present; with granules; length less than one third of the disc radius; scalene (oblique) triangular.

VENTRAL DISC. Gonads restricted to the disc. Ventral interradii with granules. Scales on ventral interradii covering the whole area of an interradius. The number of scales on H line of an interradius more than 21. 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; single row of lateral papillae; rounded (Ophiotreta) or spiniform (Ophiocomina). Adoral shield spine present. Lyman’s ossicle present. Oral shield covering less than one third of interradius; about as long as wide (Ophiotreta), or much wider than long (Ophiocomina). 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 ventral half widest; entire (Ophiocomina) or fragmented (Ophiotreta, Ophiocopa). Dental sockets slit-shaped and circular; less than 50% of the width or equal to or more 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 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.