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Synoptic Keys to the Genera of Ophiuroidea

Family Ophiomyxidae Ljungman, 1866

Family Ophiomyxidae Ljungman, 1866

1 (36)

Oral shields small; adoral plates long and slender, lying between the oral shield and the first lateral arm-plate. Vertebrae long and slender, their articular peg well developed (i.e., zygospondylous).

Subfamily Ophiomyxinae

2 (19)

Second oral tentacle-pores opening partly or entirely outside mouth-angles.

3 (16)

Teeth present, in a single vertical row.

4 (7)

Radial shields present.

5 (6)

Radial shields large, each with a conspicuous spine at the proximal end. . . . Ophiostyracium H. L. Clark, 1911.

*trachyacanthum H. L. C., 1911. North Pacific. 400 fms.

6 (5)

Radial shields small, and only their distal ends visible at arm-base. . . . Astrogeron Verrill, 1899.

H. L. Clark regards this as a synonym of Ophiogeron.

*Ophiogeron supinus Lym., 1883. West Indies. 200–400 fms.

7 (4)

No radial shields.

8 (9)

No ventral arm-plates, except on the first arm-segment. . . . Ophiocanops Koehler, 1922a.

Ophiocanops is keyed here as a practical convenience, as the characters of the gonads and stomach may escape notice. See Family Ophiocanopidae, p. 15.

9 (8)

Ventral arm-plates present.

10 (11)

Disc delicately scaled above. Oral papillae, teeth spiniform. Spines on outer segments are replaced by minute umbrella-shaped spinules. . . . Ophiohelus Lyman, 1880.

*umbella Lyman, 1880. West Indies. 100 fms.

11 (10)

Disc without scales.

12 (15)

Oral angles devoid of oral papillae.

13 (14)

Disc covered by naked skin. . . . Ophiogeron Lyman, 1878.

*edentulus Lyman, 1878. Fiji. 1,350 fms.

14 (13)

Disc covered by finely granulated skin. . . . Ophiosciasma Lyman, 1878.

*attenuatum Lyman, 1878. E. Brazil. 350 fms.

15 (12)

Oral angles bearing spiniform oral papillae, which resemble the teeth and tooth papillae. . . . Ophioscolex (s.s.) Mueller & Troschel, 1842. The genus was restricted by Mortensen (1933); synonym Ophiocynodus H. L. Clark, 1911.

*glacialis M. & T., 1842. Arctic. 100 fms.

page 14
16 (3)

Teeth vestigial; resembling spinules.

17 (18)

Uppermost arm-spines of successive segments united to one another by a horizontal membrane running longitudinally along the arm. No dorsal arm-plates. . . . Ophiosyzygus H. L. Clark, 1911.

*disacanthus H. L. C., 1911. Japan. 100 fms.

18 (17)

No membrane uniting arm-spines: thin hyaline dorsal arm-plates. . . . Ophioleptoplax H. L. Clark, 1911.

*megapora H. L. C., 1911. North Pacific. 70 fms.

19 (2)

Second oral tentacle opening entirely within the mouth-angles.

20 (29)

Teeth and oral papillae acutely pointed.

21 (22)

Conspicuous radial shields, disc scaled above and below; dorsal arm-plates present: 1 tentacle scale: distal part of arm, the upper 2 arm-spines are modified into double hooklets. . . . Ophiolycus Mortensen, 1933c. *inermis Mrtsn., 1933c. S. Africa. 200 fms.

22 (21)

Radial shields not distinguishable from other plates, or lacking altogether. No dorsal arm-plates.

23 (24)

A conspicuous coating of large granules covers the dorsal surface of the disc and arms. . . . Ophiovesta Koehler, 1931.

*granulata Koehler, 1931. Indonesia. Littoral.

24 (23)

Platelets or granules form a conspicuous marginal border round the disc, which is otherwise covered by skin.

25 (28)

Genital cleft shorter than an arm-segment.

26 (27)

No tentacle scale: arm-spines hyaline with several hooklets. . . . Ophiostiba Matsumoto, 1915.

*hidekii Matsumoto, 1915. Japan. 300 fms.

27 (26)

Single tentacle-scale: arm-spines not hooked. . . . Ophiomora Koehler, 1907.

*elegans Koehler, 1907. East Africa.

28 (25)

Genital cleft as long as 4 arm-segments: 6 or 7 short, blunt arm-spines. . . . Neoplax Bell, 1884.

*ophiodes Bell, 1884. Indian O. Littoral.

29 (20)

Teeth and oral papillae broadly expanded with denticulate free margins.

30 (33)

Disc plates present around the margin, disc otherwise covered by skin.

31 (32)

Dorsal arm-plates entire: radial shields rudimentary: arm-spines modified as compound hooks. . . . Ophiohyalus Matsumoto, 1915.

*gotoi Matsumoto, 1915. Japan.

32 (31)

Dorsal arm-plates fragmented; radial shields conspicuous: arm-spines not hooked, save at tip of arm. . . . Ophiomyxa Mueller & Troschel, 1840.

*Ophiura pentagona Lmk., 1816. Mediterranean.

33 (30)

No marginal disc-plates.

34 (35)

No radial shields: arm-spines webbed. . . . Ophiohymen H. L. Clark, 1911.

*gymnodiscus H. L. C., 1911. North Pacific. 100 fms.

35 (34)

Radial shields present: arm-spines free. . . . Ophiodera Verrill, 1899.

*serpentaria Lyman, 1883. N. Atlantic. 350 fms.

H. L. Clark (1915) refers the type to Ophiomyxa. Mortensen (1927) synonymizes Ophiodera with Ophiomyxa.

36 (1)

Oral shields and adoral plates fused together and very thick: adoral plates lying proximal to the oral shields. Vertebrae short, thick, their articular peg page 15rudimentary or absent (i.e., streptospondylous). . . .

Subfamily Ophiobyrsinae

37 (38)

Only 1 genital cleft in each interradius: oral shield present in only 1 interradius. . . . Ophioschiza H. L. Clark, 1911.

*monacantha H. L. C., 1911. Bering Sea. 300 fms.

38 (37)

Genital clefts paired: 5 oral shields.

39 (44)

Radial shields conspicuous, elongate, bearing spinules.

40 (41)

No dorsal arm-plates: arm-spines very long and serrated. . . . Ophiophrixus H. L. Clark, 1911.

*acanthinus H. L. C., 1911. Japan. 100 fms.

41 (40)

Fragmented dorsal arm-platelets occur: arm-spines not long, nor serrated.

42 (43)

Oral papillae forming a regular lateral row along the sides of the oral angle: ca. 5 spiniform teeth at jaw-apex, as well as dental papillae. . . . Ophiobyrsella Verrill, 1899.

*serpens Lyman, 1883. Caribbean. 70 fms.

H. L. Clark (1915) refers the type to Ophiobyrsa.

43 (42)

Only 1 oral papilla, and no teeth: a few spiniform dental papillae at the jaw-apex. . . . Ophiobyrsa Lyman, 1878.

*rudis Lyman, 1878. Australia. Littoral.

44 (39)

Radial shields inconspicuous or absent.

45 (46)

Only lateral arm-plates on arm: 1 oval tentacle-scale. . . . Astrogymnotes H. L. Clark, 1914.

Referred by H. L. Clark and Doederlein to Trichasteridae: but Mortensen states vertebrae are zygospondylous: the solitary genotype is hexamerous, and this character may prove to be generic.

*catasticta H. L. C., 1914. W. Australia. 100 fms.

46 (45)

Ventral arm-plates as well as lateral arm-plates.

47 (48)

Disc bearing spinules: oral and dental papillae spiniform. . . . Ophiobrachion Lyman, 1883.

*uncinatus Lyman, 1883. Cuba. 250 fms.

48 (47)

Disc free from spinules: oral and dental papillae, and teeth, all alike, stout, stumpy, blunt and thorny at the tip. . . . Ophiosmilax Matsumoto, 1915.

*mirabilis Matsumoto, 1915. Japan. 300 fms.