Ophiuroidea Gray 1840

Conventional identification key to the families of the Ophiuroidea with respect to the species listed in Table 1

1. Longest arm spines shorter than half a segment........................................................................ 2

– Longest arm spines between half and one segment long........................................................ 12

– Longest arm spines between one and two segments long....................................................... 20

– Longest arm spines longer than two segments........................................................................ 32

2(1). Arm spines tapering (conical) (Fig. 5)...................................................................................... 3

– Arm spines flat (Fig. 5)........................................... Ophiodermatidae Ljungman, 1867 [p. 34]

– Arm spines cylindrical (Fig. 5).................................................................................................. 4

– Arm spines pointed (Fig. 5)....................................................................................................... 6

3(2). Arm combs present (Fig. 1F); dorsal arm plate present; spines all similar in shape (Fig. 5); arm spines mainly lateral......................................................... Ophiopyrgidae Perrier, 1893 [p. 25]

– Arm combs absent; dorsal arm plate absent; spines not all similar in shape (Fig. 2F–H); arm spines at proximal segments only on ventral side of arms.... Asteronychidae Ljungman, 1867 [p. 19]

4(2). Radial shield scalene (oblique) triangular (Fig. 1E)......... Astrophiuridae Sladen, 1879 [p. 24]

– Radial shield isosceles (mirror-symmetric) triangular to pear-shaped (Fig. 1F)....................... 5

– Radial shield bar-like (Fig. 1B).................................................. Euryalidae Gray, 1840 [p. 20]

5(4). Arm combs present (Fig. 1F); arm spines mainly lateral; tentacle scales more than two times as long as wide; dorsal disc scale/plate without tubercles (Fig. 2B–D)..................................................................................................................................... Ophiopyrgidae Perrier, 1893 [p. 25]

– Arm combs absent; arm spines at proximal segments only on ventral side of arms; tentacle scales nearly as long as wide; dorsal disc scale/plate with tubercles (Fig. 2A).............................................................................................................................. Hemieuryalidae Verrill, 1899 [p. 40]

6(2). Tentacle scales nearly as long as wide....................................................................................... 7

– Tentacle scales slightly longer than wide.................................................................................. 8

– Tentacle scales more than two times as long as wide.............................................................. 10

7(6). Tentacle scales shorter than the spine nearby; tentacle scales cross section round; disc pentagonal; dorsal disc with spines (Fig. 2B–D)................... Ophiosphalmidae O’Hara et al., 2018 [p. 22]

– Tentacle scales as long as the spine nearby; tentacle scales cross section oval; disc circular; dorsal disc without spines (Fig. 1A–B, D–F).............................. Astrophiuridae Sladen, 1879 [p. 24]

8(6). Accessory dorsal arm plate present; dorsal disc with obvious primary plates (Fig. 2D); adoral shield meeting in front of the oral shield; distance between spine articulations dorsalwards increasing.................................................................... Ophiolepididae Ljungman, 1867 [p. 39]

– Accessory dorsal arm plate absent; dorsal disc with concealed primary plates (Fig. 1A–D); adoral shield separated (Fig. 4); distance between spine articulations equal....................................... 9

9(8). Arm spines predominantly parallel to arm axis (adpressed); integument obscuring plates (Fig. 1D); dorsal disc without scales; dorsal disc with spines (Fig 2B, D)..................................................................................................................................... Ophiopezidae O’Hara et al., 2018 [p. 35]

– Arm spines predominantly erect, standing perpendicular to arm axis; integument not obscuring plates (Fig. 1E–F); dorsal disc with scales (Fig. 2B, D); dorsal disc without spines (Fig.1A–B, D–F)............................................................................. Ophiomyxidae Ljungman, 1867 [p. 36]

10(6). Arm combs present (Fig. 1F); disc circular; genital papillae present; distance between spine articulations dorsalwards increasing.................................. Ophiopyrgidae Perrier, 1893 [p. 25]

– Arm combs absent; disc pentagonal; genital papillae absent; distance between spine articulations equal.........................................................................................................................................11

11(10). Arm spines predominantly parallel to arm axis (adpressed); tentacle scales longer than the spine nearby; tentacle pores visible only on proximal arm; dorsal disc with obvious primary plates (Fig. 2D)................................................................. Ophiomusaidae O’Hara et al., 2018 [p. 23]

– Arm spines predominantly erect, standing perpendicular to arm axis; tentacle scales shorter than the spine nearby; tentacle pores visible along most of the arm; dorsal disc with concealed primary plates (Fig. 1B–D)....................................................... Ophiomyxidae Ljungman, 1867 [p. 36]

12(1). Arm spines predominantly parallel to arm axis (adpressed)................................................... 13

– Arm spines predominantly erect, standing perpendicular to arm axis.................................... 16

13(12). Tentacle scales nearly as long as wide..................................................................................... 14

– Tentacle scales slightly longer than wide................................................................................ 15

– Tentacle scales more than two times as long as wide....... Ophiopyrgidae Perrier, 1893 [p. 25]

14(13). Arm spines cylindrical (Fig. 5); radial shield isosceles (mirror-symmetric) triangular to pearshaped (Fig. 1F); the ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.9–1 (Fig. 5); arm spines at proximal segments only on ventral side of arms................................................................................. Hemieuryalidae Verrill, 1899 [p. 40]

– Arm spines pointed (Fig. 5); radial shield scalene (oblique) triangular (Fig. 1F); the ratio of thickness of distal ⅓ of arm spine to maximum thickness (in a given cross-sectional plane) 0.6–0.9 (Fig. 5); arm spines mainly lateral................. Ophioleucidae Matsumoto, 1915 [p. 38]

15(13). Arm combs present (Fig. 1F); spines all similar in shape; arm spine cross section round (Fig. 5); integument not obscuring plates (Fig. 1E–F)...... Ophiuridae Müller & Troschel, 1840 [p. 24]

– Arm combs absent; spines not all similar in shape (Fig. 2F–H); arm spine cross section oval (Fig. 5); integument obscuring plates (Fig. 1D)......... Ophiernidae O’Hara et al., 2018 [p. 37]

16(12). Integument not obscuring plates (Fig. 1E–F); nerve opening approximately as large as muscle opening.................................................................................................................................... 17

– Integument obscuring plates (Fig. 1D); nerve opening smaller than muscle opening........... 18

17(16). Tentacle scales nearly as long as wide; radial shield length between one third and half of the disc radius; arm spine articulation ventralwards increasing in size........................................................................................................................................... Amphiuridae Ljungman, 1867 [p. 44]

– Tentacle scales slightly longer than wide; radial shield length more than half of the disc radius; arm spine articulation larger in middle of arm............... Ophiactidae Matsumoto, 1915 [p. 46]

18(16). Arm covering without granules/spines/tubercles; arm spine cross section round (Fig. 5); arm spines mainly lateral; genital slit longer than half the length of an interradius....................... 19

– Arm covering with granules; arm spine cross section oval (Fig. 5); arm spines at proximal segments only on ventral side of arms; genital slit shorter than half the length of an interradius.............................................................................. Gorgonocephalidae Ljungman, 1867 [p. 21]

19(18). Tentacle scales present; dorsal disc with scales (Fig. 2B, D); radial shield without granules/spines (Fig. 1B); ventral teeth single (Fig. 4)..................... Ophionereididae Ljungman, 1867 [p. 42]

– Tentacle scales absent; dorsal disc without scales; radial shield with granules (Fig. 1A); ventral teeth several (tooth papillae) (Fig. 4)........................ Ophiobyrsidae Matsumoto, 1915 [p. 29]

20(1). Integument not obscuring plates (Fig. 1E–F).......................................................................... 21

– Integument obscuring plates (Fig. 1D).................................................................................... 26

21(20). Radial shield length between one third and half of the disc radius......................................... 22

– Radial shield length more than half of the disc radius............................................................ 25

22(21). Arm combs present (Fig. 1F); arm spines predominantly parallel to arm axis (adpressed); tentacle scales slightly longer than wide; ventral teeth several (tooth papillae) (Fig. 4)....................................................................................................... Ophiuridae Müller & Troschel, 1840 [p. 24]

– Arm combs absent; arm spines predominantly erect, standing perpendicular to arm axis; tentacle scales nearly as long as wide; ventral teeth single (Fig. 4)..................................................... 23

23(22). Accessory dorsal arm plate present; accessory ventral arm plate present; spines not all similar in shape (Fig. 2F–H); dorsal and/or ventral edge(s) of LAPs with constriction (Fig. 2I)........................................................................................... Ophiopholidae O’Hara et al., 2018 [p. 47]

– Accessory dorsal arm plate absent; accessory ventral arm plate absent; spines all similar in shape; dorsal and/or ventral edge(s) of LAPs without constriction (Fig. 2J).................................... 24

24(23). The number of scales on H line (Fig. 2C) of an interradius about 7–14; arm spine articulation larger in middle of arm; dental plate ventral half widest; dental sockets less than 50% of the width.................................................................... Ophiothamnidae O’Hara et al., 2018 [p. 46]

– The number of scales on H line (Fig. 2C) of an interradius about 14–21; arm spine articulation ventralwards increasing in size; dental plate dorsal half widest; dental sockets equal to or more than 50% of the width.................................................... Amphiuridae Ljungman, 1867 [p. 44]

25(21). Tentacle scales present; dorsal disc with spines (Fig. 2B, D); arm spine articulation larger in middle of arm; nerve opening approximately as large as muscle opening.......................................................................................................................... Ophiactidae Matsumoto, 1915 [p. 46]

– Tentacle scales absent; dorsal disc without spines (Fig. 1A–B, D–F); arm spine articulation ventralwards increasing in size; nerve opening smaller than muscle opening.............................................................................................................. Amphilepididae Matsumoto, 1915 [p. 45]

26(20). Tentacle scales nearly as long as wide..................................................................................... 27

– Tentacle scales slightly longer than wide................................................................................ 28

– Tentacle scales more than two times as long as wide.............................................................. 30

27(26). Arm spines flat; the number of scales on H line (Fig. 2C) of an interradius more than 21; arm spine cross section oval (Fig. 5); ventral teeth several (tooth papillae) (Fig. 4)................................................................................................................... Ophiotomidae Paterson, 1985 [p. 30]

– Arm spines pointed (Fig. 5); the number of scales on H line (Fig. 2C) of an interradius about 7–14; arm spine cross section round (Fig. 5); ventral teeth single (Fig. 4)..................................................................................................................... Ophiacanthidae Ljungman, 1867 [p. 33]

28(26). Arm spines predominantly parallel to arm axis (adpressed); radial shield absent (Fig. 1C); ventral interradii with spines; ventro-distal tip of LAP projecting ventralwards (Fig. 2K).................................................................................................................. Ophiohelidae Perrier, 1893 [p. 27]

– Arm spines predominantly erect, standing perpendicular to arm axis; radial shield present; ventral interradii with granules; ventro-distal tip of LAP not projecting ventralwards (Fig. 2L)....... 29

29(28). Radial shield scalene (oblique) triangular; the number of scales on H line (Fig. 2C) of an interradius more than 21; arm spine cross section oval (Fig. 5); radial shield with granules............................................................................................... Ophiotomidae Paterson, 1985 [p. 30]

– Radial shield isosceles (mirror-symmetric) triangular to pear-shaped (Fig. 1F); the number of scales on H line (Fig. 2C) of an interradius about 14–21; arm spine cross section round (Fig. 5); radial shield without granules/spines (Fig. 1B)....... Ophionereididae Ljungman, 1867 [p. 42]

30(26). Tentacle scales shorter than the spine nearby; the number of scales on H line (Fig. 2C) of an interradius about 14–21; oral shield covering less than one third of interradius; at least one socket on DP as depression or perforation without septum................................................................ 31

– Tentacle scales longer than the spine nearby; the number of scales on H line (Fig. 2C) of an interradius more than 21; oral shield covering more than one third of the length of an interradius; at least one socket on DP as perforation with septum....................................................................................................................................................... Ophiopsilidae Matsumoto, 1915 [p. 43]

31(30). Arm spine cross section round (Fig. 5); tentacle scales cross section oval; radial shield absent (Fig. 1C); ventral interradii without granules/spines.... Ophioscolecidae Lütken, 1869 [p. 28]

– Arm spine cross section oval (Fig. 5); tentacle scales cross section round; radial shield present (Fig. 1C); ventral interradii with spines................ Amphilimnidae O’Hara et al., 2018 [p. 41]

32(1). Radial shield length less than one third of the disc radius...................................................... 33

– Radial shield length between one third and half of the disc radius......................................... 35

– Radial shield length more than half of the disc radius............................................................ 36

33(32). Radial shield scalene (oblique) triangular (Fig. 1E); arm spine cross section oval (Fig. 5); integument obscuring plates (Fig. 1D); radial shield with granules (Fig. 1A)....................... 34

– Radial shield isosceles (mirror-symmetric) triangular to pear-shaped (Fig. 1F); arm spine cross section round (Fig. 5); integument not obscuring plates (Fig. 1E–F); radial shield without granules/spines (Fig. 1B)............................................ Ophiomyxidae Ljungman, 1867 [p. 36]

34(33). Adoral shield separated; ventral position of LAP projecting ventro-proximalwards (Fig. 2K); disc flat (about same level as arms); lateral oral papillae multiple rows of lateral papillae.............................................................................................. Ophiocomidae Ljungman, 1867 [p. 36]

– Adoral shield meeting in front of the oral shield; ventral position of LAP not projecting ventroproximalwards (Fig. 2L); disc high (above arm level); lateral oral papillae single row of lateral papillae (Fig. 2E)............................................................. Ophiotomidae Paterson, 1985 [p. 30]

35(32). Arm covering without granules/spines/tubercles; arm spines pointed (Fig. 5); tentacle scales nearly as long as wide; integument obscuring plates (Fig. 1D)...................................................................................................................................... Ophiacanthidae Ljungman, 1867 [p. 33]

– Arm covering with tubercles grown out of scales/plates; arm spines cylindrical (Fig. 5); tentacle scales slightly longer than wide; integument not obscuring plates (Fig. 1E–F)........................................................................................................ Ophiocamacidae O’Hara et al., 2018 [p. 29]

36(32). Tentacle scales nearly as long as wide..................................................................................... 37

– Tentacle scales more than two times as long as wide............................................................. 38

37(36). Accessory ventral arm plate present; tentacle scales cross section round; scales on ventral interradii absent; ventral teeth several (tooth papillae) (Fig. 4).................................................................................................................................... Ophiopteridae O’Hara et al., 2018 [p. 31]

– Accessory ventral arm plate absent; tentacle scales cross section oval; scales on ventral interradii covering the whole area of an interradius; ventral teeth single (Fig. 4).......................................................................................................................... Ophiacanthidae Ljungman, 1867 [p. 33]

38(36). Arm spines flat (Fig. 5); tentacle scales shorter than the spine nearby; arm spine cross section oval (Fig. 5); tentacle scales cross section oval........ Clarkcomidae O’Hara et al., 2018 [p. 32]

– Arm spines pointed (Fig. 5); tentacle scales as long as the spine nearby; arm spine cross section round (Fig. 5); tentacle scales cross section round..... Ophiotrichidae Ljungman, 1867 [p. 48]