ILYOPHINAE

Tighe, Kenneth A., Smith, David G., Merrett, Nigel R., Frable, Benjamin W. & Zajonz, Uwe, 2024, Redescription of the eel Ilyophis arx Robins, 1976 (Anguilliformes: Synaphobranchidae: Ilyophinae) with a description of a new species of Ilyophis, and a taxonomic synopsis of the Ilyophinae, Zootaxa 5506 (1), pp. 35-57 : 53-55

ARTIFICIAL KEY TO THE SPECIES OF ILYOPHINAE

1a. Vomerine teeth compound, uniserial...................................................................... 2

1b. Vomerine teeth simple, in one or more rows............................................................... 23

2a. Pectoral fins absent................................................................................... 3

2b. Pectoral fins present.................................................................................. 9

3a. Trunk very short, about half head length................................................ Dysomma brachygnathos

3b. Trunk longer, about twice head length.................................................................... 4

4a. Three large intermaxillary teeth projecting downward from tip of snout in front of lower jaw............ Dysomma tridens

b. Two intermaxillary teeth, not projecting from snout.......................................................... 5

5a. Tip of snout and chin bulbous, with conspicuous papillae and ridges; vertebrae greater than 190..... Dysomma brevirostre

5b. Snout only modestly ornamented, papillae not obvious; vertebrae less than 165.................................... 6

6a. Lateral line complete.................................................................................. 7

6b. Lateral line incomplete, ca. 8–12 pores only................................................................ 8

7a. Supraorbital pores 3; trunk about 2 times head length; peritoneum black....................... Dysomma achiropteryx

7b. Supraorbital pores 4; trunk about 3 times head length; peritoneum pale........................ Dysomma bussarawati

8a. Infraorbital pores 5; trunk about 2 times head length.......................................... Dysomma muciparus

8b. Infraorbital pores 4; trunk about 3 times head length.................................... Dysomma dolichosomatum

9a. Intermaxillary teeth absent............................................................................ 10

9b. Intermaxillary teeth present............................................................................ 18

10a. Vomerine teeth consisting of 7‒8 long, needle-like compound teeth............................ Linkenchelys multipora

10b. Vomerine teeth consisting of 3‒5 heavy, conical compound teeth.............................................. 11

11a. Head length greater than trunk......................................................................... 12

11b. Head length less than trunk............................................................................ 14

12a. Total vertebrae 137‒141............................................................... Dysommina orientalis

12b. Total vertebrae less than 135........................................................................... 13

13a. Predorsal vertebrae 12‒13, preanal vertebrae 23‒25........................................... Dysommina brevis

13a. Predorsal vertebrae 14‒15, preanal vertebrae 28‒31........................................... Dysommina rugosa

14a. Lower jaw longer than upper, jaws not closing completely.................................... Dysomma melanurum

14b. Jaws equal or upper jaw longer; jaws close completely...................................................... 15

15a. Snout slender, elongate (ca. 26‒32% of HL), jaw length long (ca. 42‒52% HL); supraorbital pores 5, infraorbital pores 8, preoperculomandibular pores 9........................................................ Dysomma longirostrum

15b. Snout and jaws not notably slender and elongate); supraorbital pores 3, infraorbital pores 4‒6, preoperculomandibular pores 6‒8............................................................................................... 16

16a. Dorsal-fin origin anterior to pectoral-fin base................................................. Dysomma goslinei

16b. Dorsal-fin origin above or posterior to pectoral-fin base..................................................... 17

17a. Lateral line complete; dorsal fin origin lightly behind pectoral-fin base......................... Dysomma phukutensis

17b. Lateral line incomplete, vertebrae 122‒124; dorsal fin origin above pectoral-fin base.............. Dysomma robinsorum

18a. Trunk long, about twice head length..................................................................... 19

18b. Trunk short, less than head length....................................................................... 21

19a. Two intermaxillary teeth, arranged transversely......................................... Dysomma opisthoproctus

19b. Intermaxillary teeth in a rounded patch................................................................... 20

20a. Total vertebrae 186–199......................................................... Atractodenchelys robinsorum

20b. Total vertebrae 168–173.............................................................. Atractodenchelys phrix

20c. Total vertebrae 155–158......................................................... Atractodenchelys brevitrunca

21a. Dentary teeth numerous, 24–40; total vertebrae 107–109...................................... Dysomma bucephalus

21b. Dentary teeth fewer than 25; total vertebrae 119 or more..................................................... 22

22a. Lateral line pores 57–75; dentary teeth 6–11; total vertebrae 119–128........................... Dysomma anguillare

22b. Lateral line pores 17–33; dentary teeth 14–22; total vertebrae 128–133............................ Dysomma formosa

22c. Lateral line pores 20–49; dentary teeth 6–15; total vertebrae 134–140.......................... Dysomma taiwanense

22d. Lateral line pores 57–58; dentary teeth 8; total vertebrae 115.................................. Dysomma alticorpus

22e. Lateral line pores 57–63, dentary teeth 16–21; total vertebrae 119–124....................... Dysomma fuscoventralis

22f. Lateral line pores 65–84; dentary teeth 23–25; total vertebrae 128–140......................... Dysomma polycatodon

22g. Lateral line pores 70–79, dentary teeth 8–9; total vertebrae 118–124.......................... Dysomma intermedium

23a. Head length greater than trunk......................................................................... 24

23b. Head length less than trunk............................................................................ 25

24a. Vomerine teeth biserial; vertebrae 173–178................................................... Meadia abyssalis

24b. Vomerine teeth triserial; vertebrae 198–206...................................................... Meadia roseni

25a. Full complement of head pores: supraorbital 5, infraorbital 7–8, preoperculomandibular 10–11, 1–2 frontal, 2–3 supratemporal...................................................................................... 26

25b. Head pores reduced:: supraorbital 3, infraorbital 4–7, preoperculomandibular 6–10, no frontal or supratemporal........ 27

26a. Body partially scaled or naked; gill slit noticeably oblique; preanal Lateral line pores 37–44; total vertebrae 177–188.............................................................................................. Ilyophis blachei

26b. Body completely scaled; gill slit nearly horizontal; preanal Lateral line pores 32–37; total vertebrae 141–147..................................................................................................... Ilyophis nigeli

27a. Scales present...................................................................................... 28

27b. Scales absent....................................................................................... 29

28a. Preanal lateral line pores 33–38; total vertebrae 145–151........................................ Ilyophis brunneus

28b. Preanal lateral line pores 26–30; total vertebrae 131–134....................................... Ilyophis maclainei

29a. Head slender and conical, snout pointed; total vertebrae 141...................................... Ilyophis robinsae

29b. Head shorter, snout blunt; total vertebrae 116–135.......................................................... 30

30a. Total vertebrae less than 125........................................................................... 31

30b. Total vertebrae greater than 125........................................................................ 32

31a. Lateral line almost complete, extending nearly to caudal fin base; cephalic lateralis pores reduced: SOC 3, IO 4, POM 7; total vertebrae 118–122.......................................................................... Meadia minor

31b. Lateral line incomplete (66–80% TL); cephalic lateralis pores: SOC 3, IO 7–8 (extending behind eye), POM 8–10; total vertebrae 116–118...................................................................... Ilyophis singularis

32a. Lateral line incomplete; pored lateral line, limited to anterior third of body (ca. 35–45% TL); total lateral line pores 31–47............................................................................................ Ilyophis arx

32b. Lateral line incomplete; pored lateral line longer, extending further along total length of body (ca. 55–62 % TL); total lateral line pores 66–75....................................................................... Ilyophis saldanhai