One or more basal lateral arm-plates greatly enlarged: genital clefts in-conspicuous or altogether lacking, as a result of the encroachment of the lateral plates upon the ventral interradii: disc covered mainly by primaries or radial shields.

Only the first lateral arm-plate enlarged.

Radial shields conspicuous: enlarged first lateral plates confined to ventral side of disc, and separated interradially by the oral shield: no dorsal arm-plates: tentacle-pores widely separated. . . . Ophiochorus H. L. Clark, 1939.

*granulatus H. L. C., 1939. Zanzibar. 1,500 fms.

Radial shields inconspicuous: the structures which Clark calls the "radial shields" in his description of the holotype are evidently enlarged first lateral arm-plates. Each enlarged lateral plate extending to meet its fellow of the adjacent arm, so that the whole circular disc is invested by a ring of laterals: disc therefore not sharply demarcated from arms: oral shield small, lying proximal to the contiguous laterals: small dorsal arm-plates present: tentacle-pores close together. . . . Ophiuraster H. L. Clark, 1939.

*perissus H. L. C., 1939. Aden. 1,100 fms.

Two or more basal lateral arm-plates enlarged.

First two basal lateral arm-plates enlarged, but both confined to ventral side of disc.

The first pair of lateral plates produced into several rounded lobes, which overlie and partly obscure the oral shield: the second pair of lateral plates with similar but smaller lobes overlying the genital cleft: dorsal and ventral arm-plates extending to the arm-tip. . . . Ophiochrysis Koehler, 1904.

*ornata Koehler, 1904. Indonesia. 700 fms.

The first pair of lateral plates meeting distally on the interradial midline, surrounding the small oral shield: small dorsal and ventral arm-plates on the proximal half of arm. . . . Ophiomisidium Koehler, 1914.

*speciosum Koehl., 1914. Off Brazil. 800 fms.

Five or more basal lateral arm-plates enlarged.

Lateral plates of the 5 proximal arm-joints widened, carry 2 or 3 broad flattened spines with serrate outer edge: the enlarged lateral plates do not become fused together to form a continuous pentagonal disc. . . . Ophiophycis Koehler, 1901.

*mirabilis Koehler, 1901. Azores. 600 fms.

Lateral plates of the first 9 arm-joints expanded inter-radially and fused to the disc-proper, to make a pentagonal suctorial structure, by which the animal adheres to substrate, with the help of the tube-feet: no oral shield: adoral shields separated, adjoining the first ventral arm-plate of the corresponding side: no genital clefts. . . . Astrophiura Sladen, 1879.

*permira Sladen, 1879. Madagascar. ? sublittoral.

Basal lateral arm-plates not enlarged.

13 (16) Disc covered above by soft skin, with only the distal ends of the radial shields exposed, though other scales may be revealed if the skin is dried: tentacle-pores bordered by papillae.

An arm-comb present: only scattered irregular scales embedded in dorsal skin of disc: 7 or 8 arm-spines. . . . Gymnophiura Lütken & Mortensen, 1897.

*mollis L. & M., 1897. Gulf of Panama. 1,300 fms.

No arm-comb: a complete covering of scales beneath the skin: 3 small arm-spines. . . . Ophiopleura Danielssen & Koren, 1877.

Syn.: Lütkenia Duncan.

*borealis D. & K., 1877. Arctic. 200 fms.

Disc covered above by naked plates or scales.

Each dorsal arm-plate fragmented into a central plate, with several lateral mosaic platelets on either side. . . . Ophionotus Bell, 1902.

*victoriae Bell, 1902. Antarctica. Littoral.

Dorsal arm-plates not fragmented.

Primary plates in direct contact with arm-bases, there being no radial shields: only 1 large scale-like oral papilla. . . . Ophiotypa Koehler, 1897.

*simplex Koehler, 1897. Indian O. 2,000 fms.

Primary plates not directly touching arm-plates.

First dorsal arm-plate divided longitudinally, on the midline, into 2 equal plates, each carrying a row of papillae on the outer edge, beside the main arm-comb. . . . Dictenophiura H. L. Clark, 1923.

*Ophiura carnea Ltk., 1858. N. Europe. 40–300 fms.

Not so.

Radial shields contiguous proximally, but separated distally by a conspicuous triangular plate wedged into the disc-margin: the three sides of this plate carry minute papillae: oral shield elongate, occupying most of the interbrachium below: arms flattened, broad at base. . . . Ophiocrossota H. L. Clark, 1928.

*Ophioglypha multispina Ljung., 1867. E. Australia. Littoral.

Radial shields not separated by a triangular plate whose margins carry papillae.

Fine granulation covers upper surface of disc and extends on to part of lower surface. Radial shields short, oval, widely separated by numerous small platelets and by granulation. No arm-comb. . . . Ophiogona Studer, 1876.

Syn.: Ophiagona Lütkin, 1877; Ophiomaria A. H. Clark, 1916.

*laevigata Studer, 8716. Kerguelen. Littoral.

Not so.

Tentacle-pores restricted to a few basal arm-joints.

Disc distinctly higher than the arms.

Genital clefts bordered on their proximal interradial side by several plates which distally are continuous with a row of papillae, forming a rudimentary arm-comb: dorsal side of disc bearing larger plates with belts of smaller ones around them: arms higher than broad: 2 arm-spines, 2 tentacle-scales. . . . Ophiurolepis Matsumoto, 1915, emend. Koehler, 1922.

*Ophiolepis carinata Studer, 1876. Kerguelen and Heard Is. 75 fms.

Genital clefts without proximal interradial plates: well-developed arm-comb of prominent spinules: dorsal side of disc mainly covered by large primary plates: 3 arm-spines, 1 or no tentacle-scales. . . . Aspidophiura Matsumoto, 1915.

*watasei Mats., 1915. Japan.

Disc low and flat.

No distinct tentacle-scales: first tentacle-pore large, the others very small: disc covered by scales. . . . Ophioplinthus Lyman, 1878.

(The tentacle-pores are sometimes provided with an ill-defined "burr" or vestigial scale.)

*medusa Lyman, 1878. Antarctica. 2,000 fms.

Tentacle-scales distinct: disc covered by tumid plates.

Arm-spines minute; primary plates large, circular, with smaller plates between. . . . Homalophiura H. L. Clark, 1915.

*Ophioglypha inornata Lyman, 1878. Mid-Atlantic. 1,850 fms.

Arm-spines not minute.

A large keel-like plate at the base of the arm, more or less obscuring the radial shields: arms compressed, triangular in sections, because the dorsal plates stand high and keel-like, giving a serrated outline to the arm: 5 or more similar arm-spines. . . . Ophiosteira Bell, 1902.

Syn.: Ophiomages Koehler, 1923.

*antarctica Bell, 1902. Antarctica. Littoral. 100 fms.

Three arm-spines, whereof the middle one becomes transformed into a hyaline up-turned hooklet on distal arm-joints. . . . Ophiuroglypha Hertz, 1926.

*Ophioglypha lymani Ljung. W. Antarctica. 100 fms.

Tentacle-pores occurring over most of the arm, though the proximal pores are much larger than the distal ones.

Disc high, arms not broader than high: primary plates large and conspicuous.

Arm-comb present: tentacle-pores large, with numerous scales.

Arms cylindrical, gradually tapering, with a blunt extremity: arm-spines arranged in a single row, well-spaced from one another: oral shield large. Amphiophiura Matsumoto, 1915.

*Ophioglypha bullata Wyrille Thomson, 1873. Bermuda. 2,800 fms.

Arms higher than broad, wide at the base and tapering rapidly to an acute extremity: arm-spines numerous, often dimorphic and arranged in 2 rows. Stegophiura Matsumoto, 1915.

*Ophiura nodosa Luetk., 1855. Arctic. Littoral.

No arm-comb.

No tentacle-scales: ventral interbrachium covered with fine granulation: arms short and thick: a few arm-spines. . . . Haplophiura Matsumoto, 1915.

*Ophiozona gymnopora H. L. C., 1909. E. Australia. Littoral.

Tentacle-scales present: ventral interbrachium covered by naked scales.

Centrodorsal plate small, star-shaped, with five acute interradial rays: dorsal arm-plates restricted to 2 basal arm joints, and ventral arm-plates not extending beyond the 5–7th joint: one spiniform tentacle-scale. . . . Anthophiura H. L. Clark, 1911.

*axiologa H. L. C., 1911. Aleutians. 1,200 fms.

Centrodorsal plate large, pentagonal or rounded.

One to three tentacle-scales on basal pores, one or none beyond the arm-base: adoral shields well-developed: oral papillae more or less fused together. . . . Ophiomastus Lyman, 1878.

*tegulitius Lym., 1878. Indo-W. Pacific. 1,000 fms.

Three to six tentacle-scales in basal pores: oral papillae distinct. . . . Ophiopyrgus Lyman, 1878.

(H. L. Clark (1939) has proposed O phiopyrgoides (*Ophiopyrgus trispinosus Koehler) for forms in which the dorsal arm-plates occur over most of the arm, and in which the disc-plates are relatively flatter. However, it seems probable that some species of Ophiomastus and Ophiopyrgus are growth-stages of other ophiuroids, and the generic distinction of O phiopyrgoides, in order to accommodate these forms, is dubious.)

*wyvillethomsoni Lyman, 1878. Tonga. 250 fms.

Disc low and flat, arms broader than high.

Upper surface of disc covered by regularly arranged rounded plates in two sizes, the smaller ones each with 1 prominent tubercle and arranged so as to surround the larger ones. Tentacle-pores large, rounded, with 4 spiniform tentacle-scales (fewer distad). . . . Ophiochalcis Koehler, 1931.

*aspera Koehler, 1931. Indonesia, 60 fms.

Not so.

Primary plates more or less conspicuous, but not covering much of the disc : edge of disc not emarginated at the arm-base : basal dorsal arm-plates well developed, each one sometimes carrying a transverse row of spinules : arm-comb usually continuous across arm-base. . . . Ophiocten Lütken, 1855.

*Ophiura sericea Forbes, 1852. Arctic. 100 fms.

Primary plates inconspicuous: no transverse spinules on dorsal arm-plates: tentacle-scales papilliform, on both outer and inner edges of pores, more numerous on basal arm-joints.

No arm-combs. Three small, adpressed arm-spines. . . . Ophiotjalfa Mortensen, 1915.

*vivipara Mrtsn., 1915. N. Atlantic.

Arm-comb usually present, but not continuous across arm-base: edge of disc emarginated at arm-base, and the notch so formed is occupied by several rudimentary dorsal arm-plates. . . . Ophiura Lamarck, 1801 (emend. auctt.)

Syn.: Ophioglypha Lyman, 1860. Ophioglyphina Ludwig, 1886; Ophiozea A. H. Clark, 1920.

*Asterias ophiura Linné, 1758. Europe. Littoral.