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Synoptic Keys to the Genera of Ophiuroidea

Order Ophiurida Mueller & Troschel, 1840 — (syn. Myophiuroida Matsumoto, 1915.)

Order Ophiurida Mueller & Troschel, 1840
(syn. Myophiuroida Matsumoto, 1915.)

Key to the Suborders, Families and Subfamilies

1 (8)

Disc and arms covered by thick skin which may contain a mosaic of granules but does not overlie a layer of plates or scales. Arm-spines point downwards. Arms roll into vertical coils. Vertebrae articulate by broad, hourglass-shaped surfaces. . . (Suborder EURYALAE M. & T. p. 7.)

2 (7)

Vertebrae with a ventral furrow, so that the radial canal and nerve are not imbedded in stereom; distal arm-joints not long and slender.

3 (4)

Hooks on dorsal side of arms; the hooks have no lamina and lack regularly arranged perforations; gonads restricted to disc. . . (Family GORGONOCEPHALIDAE Ljungman, 1867, emend. Mortensen, 1933. p. 7.)

4 (3)

No hooks on dorsal side of arms; but at distal end of arm the lateral arm-spines are transformed into hooks which lack a lamina and lack perforations.

5 (6)

Gonads restricted to disc. (Fam. ASTERONYCHIDAE Verrill, 1899, emend. Mortensen, 1933. p. 11.)

6 (5)

Gonads extending to at least midway along the arms. . . (Fam. ASTEROSCHEMATIDAE Verrill, 1899, restr. Mrtsn., 1933; non Matsumoto, 1915. p. 11.)

7 (2)

Vertebrae with ventral furrow closed over, so that radial canal and nerve lie within the vertebrae; distal arm-joints long and slender; no hooks on dorsal side of arms, but at distal end of arm the lateral arm-spines are transformed into hooklets with a lamina perforated by serially arranged holes. (Fam. EURYALIDAE Gray, 1840, emend. Mortensen, 1933, p. 10.)

8 (1)

Disc and arms covered by scales or plates (sometimes invested by skin or granules). Arm-spines placed laterally on arms. Arms usually move horizontally (but in Fam. Hemieuryalidae they roll vertically). . . . (Suborder OPHIURAE Mueller & Troschel, p. 12.)

9 (10)

Arms rolling vertically into tight coils. Vertebrae with broad, saddle-shaped articulations, like those of the Order Euryalae. Usually epizoic upon gorgonian corals. . . . (Fam. HEMIEURYALIDAE Verrill, 1899. p. 12.)

10 (9)

Arms bending only sideways, in the horizontal plane. Vertebrae with ball-and-socket joints, or with interlocking processes. Usually free-living, only very rarely epizoic.

page 5
Representative ophiuroids illustrating characters of systematic significance. 1, ventral aspect and, 2, dorsal aspect, of Ophiura (Fam. Ophiuridae). 3, ventral aspect of Ctenamphiura (Fam. Amphiuridae). 4, dorsal aspect of arm-joint in Ophiacantha (Fam. Ophiacanthidae). 5, distal arm-hooklet with flattened lamina which is perforated and bears a secondary (i.e., lateral) tooth, in Astroceras (Fam. Euryalidae). 6, similar arm-hooklet but lacking the flattened lamina and perforations, in Astrothorax (Fam. Gorgonocephalidae).

Representative ophiuroids illustrating characters of systematic significance. 1, ventral aspect and, 2, dorsal aspect, of Ophiura (Fam. Ophiuridae). 3, ventral aspect of Ctenamphiura (Fam. Amphiuridae). 4, dorsal aspect of arm-joint in Ophiacantha (Fam. Ophiacanthidae). 5, distal arm-hooklet with flattened lamina which is perforated and bears a secondary (i.e., lateral) tooth, in Astroceras (Fam. Euryalidae). 6, similar arm-hooklet but lacking the flattened lamina and perforations, in Astrothorax (Fam. Gorgonocephalidae).

page 6
11 (12)

Disc without ventral interradial areas. Gonads arranged serially along the arms on either side, bulging visibly below the skin. Stomach sending a dorsal radial diverticulum into each arm. . . . (Fam. OPHIOCANOPIDAE Mortensen, 1933. p. 15.)

12 (11)

Disc with conspicuous ventral interradial areas. Gonads and stomach confined to disc.

13 (16)

Thick soft skin covers the plates of disc and arms, but the underlying plates and scales become visible after drying. Arm-spines erect. . . . (Fam. OPHIOMYXIDAE Ljungman, 1866. p. 13.)

14 (15)

Oral shields small. Adoral plates long and slender, lying between the oral shield and the first lateral arm-plates. Vertebrae long and slender, the articular peg well-developed. . . . (Subfam. OPHIOMYXINAE Ljungman, 1866, restr. Matsumoto, 1915, p. 13.)

15 (14)

Oral shields and adoral plates fused together, massive. Adoral plates proximal to oral shield. Vertebrae short, thick, the articular peg rudimentary or lacking. . . . (Subfam. OPHIOBYRSINAE Matsumoto, 1915, p. 15.)

16 (13)

Disc and arms not covered by thick skin. Scales and plates easily visible, though they may carry spines or granules more or less concealing them on the disc.

17 (20)

Spiniform tooth-papillae forming a cluster at the apex of each jaw.

18 (19)

Oral papillae border each jaw. (Fam. OPHIOCOMIDAE Ljungman, 1867. p. 25.)

19 (18)

No oral papillae. (Fam. OPHIOTHRICIDAE Ljungman, 1867. p. 23.)

20 (17)

No tooth-papillae.

21 (22)

Paired infradental papillae at the apex of each jaw. . . . (Fam. AMPHIURIDAE Ljungman, 1867, p. 20.)

22 (21)

An unpaired infradental papilla at the apex of each jaw.

23 (28)

Arms inserted laterally into the disc and firmly fused to it.

24 (25)

Granulation covers over the disc-scales of both upper and lower surfaces, often also covering the jaws. . . . (Fam. OPHIODERMATIDAE Ljungman, 1867. p. 26.)

25 (24)

No granulation. . . . (Fam. OPHIURIDAE Lyman, 1865. p. 28.)

26 (27)

Second oral tentacle-pore opens more or less entirely outside the oral slits. . . . (Subfam. OPHIURINAE Lyman, 1865, restr. Matsumoto, 1915, p. 28.)

27 (26)

Second oral tentacle-pore opens entirely within the oral slit. (Subfam. OPHIOLEPIDINAE Matsumoto, 1915, p. 32.)

28 (23)

Arms inserted ventrally below the disc and partly overlain by the disc, the arms and disc not firmly fused together.

29 (36)

Free margins of jaw bear a continuous series of uniform oral papillae.

30 (33)

No granulation or spinules on disc.

31 (32)

Arms robust, not constricted at the nodes. A ventral keel on the midline of each ventral arm-plate, often also a similar keel on the dorsal arm-plates. Disc large, flat. . . . (Fam. OPHIOCHITONIDAE Matsumoto, 1915, p. 26.)

32 (31)

Arms slender, elongate, with no ventral or dorsal keels. Vertebrae long, slender, often divided longitudinally by a series of pores. . . . (Fam. AMPHILEPIDIDAE Matsumoto, 1915. p. 23.)

page 7
33 (30)

Granules or spinules present on disc. Arms slender, often constricted at the nodes. Mainly abyssal forms.

34 (35)

Arm-spines numerous, long, conspicuous, erect. . . . (Fam. OPHIACANTHIDAE Perrier, 1891. p. 15.)

35 (34)

Ann-spines few, small, inconspicuous, adpressed. . . . (Fam. OPHIOLEUCIDAE Matsumoto, 1915. p. 19.)

36 (29)

Free margins of jaw do not bear a continuous series of uniform papillae; instead, there is a diastema separating the lateral oral papillae from the dissimilar infradental papillae at the apex of the jaw. . . . (Fam. OPHIACTIDAE Matsumoto, 1915. p. 23.)