Key to the species of Apterichtus

(In that specimens of Apterichtus possess small cepehalic pores, lack scales, and are usually faded in preservative, their identification can often be difficult.)

1a. Anterior nostril without a prominent tube, its opening flush or nearly flush with underside of snout (Fig. 4A)............. 2

1b. Anterior nostril within a prominent tube (Fig. 4 B).......................................................... 3

2a. Preopercular pores 4; snout length equal to or more than twice eye diameter; trunk length 35–35% of TL; numerous small spots on head, less than eye diameter in size; MVF (Mean Vertebral Formula) 58–140, total vertebrae 138–142.................................................................................................... A. jeffwilliamsi

2b. Preopercular pores 3; snout length less than twice eye diameter; trunk length 40% of TL; small spots and a few large spots on head; VF 60–137, total vertebrae 137............................................................ A. nariculus

3a. Supratemporal pores 3; preopercular pores 3 (Fig. 3 A)........................................................ 4

3b. Supratemporal pores 5–9; preopercular pores 3 or 4 (Fig. 3 B)................................................. 10

4a. Head length 11–16 times in TL.......................................................................... 5

4b. Head length 17–21 times in TL.......................................................................... 7

5a. 3–4 vomerine teeth; total vertebrae 150–157............................................. Apterichtus anguiformis

5b. 5–7 vomerine teeth; total vertebrae 132–146................................................................ 6

6a. 5–7 vomerine teeth; preanal vertebrae 61–63; MVF 62–142, total vertebrae 137–145................ Apterichtus kendalli

6b. 4–6 vomerine teeth; preanal vertebrae 53–60; MVF 59–138, total vertebrae 132–146............. Apterichtus equatorialis

7a. None, or 1–2 vomerine teeth............................................................................ 8

7b. More than 5 vomerine teeth............................................................................. 9

8a. Tail 1.6–1.7 in TL; MVF 54–139, total vertebrae 137–141..................................... Apterichtus hatookai

8b. Tail 1.8–2.4 in TL; MVF 77–158, total vertebrae 154–166.................................. Apterichtus flavicaudus

9a. Snout sharply pointed in lateral view, dorsal profile ca. 30 O above lower jaw; snout 4.4–5.4 in HL; tip of lower jaw beneath anterior margin of orbit; anterior nostril tube 3 times in eye; MVF 82–164, total vertebrae 162–167.... Apterichtus australis

9b. Snout less pointed in lateral view, dorsal profile ca. 45–50 O above lower jaw; snout 5.1–5.8 in HL; tip of lower jaw in advance of a line beneath anterior margin of orbit; anterior nostril tube 4 times in eye; MVF 75–148, total vertebrae 146–153............................................................................................... Apterichtus mysi

10a. Supratemporal pores 7–9.............................................................................. 11

10b. Supratemporal pores 5 (rarely 6)....................................................................... 12

11a. Head length 16–20 in TL; body depth 63–71 in TL; MVF 66–143, total vertebrae 147–151.................... A. monodi

11b. Head length 12 in TL; body depth 45 in TL; MVF 54–132, total vertebrae 131–133....................... A. orientalis

12a. Preopercular pores 4................................................................................. 13

12b. Preopercular pores 3................................................................................. 15

13a. Vomerine teeth numerous, 8–14 in a single or irregularly biserial row; MVF 52–134, total vertebrae 132–139..... A. caecus

13b. 2–4 vomerine teeth; total vertebrae 123–132.............................................................. 14

14a. Body moderately elongate, body depth 43–53 in TL; tail length 1.7–1.8, head length 12–15 in TL; MVF 54–128, total verte- brae 123–132.................................................................................... A. ansp

14b. Body extremely elongate, body depth 67–100 in TL; tail length 1.7, head length 14 in TL; MVF ~52–130, total vertebrae 129–132.................................................................................... A. gracilis

15a. Total vertebrae 131–145............................................................................... 16

15b. Total vertebrae 155–162.............................................................................. 17

16a. Center of orbit above tip of lower jaw; tail 1.8–1.9 in TL; head 12–14 in TL; MVF 58–138, total vertebrae 131–145................................................................................................... A. klazingai

16b. Anterior margin of orbit behind tip of lower jaw; tail 1.9–2.1 in TL; head 16–18 in TL; MVF 66–143, total vertebrae 141–145............................................................................................. A. moseri

17a. Head length 16–17 in TL; preanal vertebrae 68–74, MVF 70–160, total vertebrae 160..................... A. dunalailai

17b. Head length 18–19 in TL; preanal vertebrae 73–80, MVF 78–158, total vertebrae 155–162................... A. malabar