Campylomormyrus Bleeker 1874

Campylomormyrus have prominent tubular snouts both laterally compressed and elongated making a downward sloping head profile. The mouth is terminal and small, with few conical or bicuspid teeth. A sub-mental filament forms a fleshy, sensory-probe sometimes extending well beyond the gape. The dorsal and anal fins originate at about the same level and are about the same length, or the dorsal is slightly shorter. The chin appendage is covered with mormyromast and ampullary electroreceptors used for active and passive electrolocation, probably for prey items buried in mud. Aquarists have reported that some Campylomormyrus may force a jet of water through the tubular snout to stir up silt on the bottom in the search for insect larvae, their predominant food.

There are 14 species generally recognized as valid (Poll et al., 1982, Gosse et al, 1984), 15 counting C. compressirostris (Pellegrin) that Feulner et al. (2007) regard as valid. All but C. phantasticus (Sanaga R.) and C. tamandua (Niger & Congo) are endemic to the Congo basin and its associated headwaters.

The snout becomes even more prolonged in adults compared to juveniles. As a consequence, some systematists now recommend an alternative standard length measurement when considering various Campylomormyrus species (Poll et al., 1982), the POSL, post-orbital standard length, or LSPO in French.

Key to the species of the genus Campylomormyrus (after Poll, Gosse & Orts, 1982, translated by J.P. Sullivan).

"Snout angle" is the angle from a straight line through the eye, parallel to the long axis of the body, to the anterior tip of the upper jaw.

1. — 12 scales around caudal peduncle (exceptionally 11 or 14). → 2.

— From 16 to 22 scales around caudal peduncle. → 8.

2. — Caudal peduncle at least 3 times as long as deep. Snout angle measuring 35° or more (35-82°). → 3.

— Caudal peduncle less than 3 times as long as deep. Snout angle measuring less than 35° (20-30°). → C. orycteropus (Poll, Gosse & Orts, 1982)

3. — Snout 4 to 6.3 times longer than deep. Body depth ranging from 3.5 to 4.5 times in postorbital standard length. → 4.

— Snout 2-4 times longer than deep. Body depth ranging from 2.8 to 3.8 times in postorbital standard length. → 6.

4. — Snout angle 47-82°. Dorsal 29-34, Anal 33-35 → 5.

— Snout angle 35-46°. Dorsal 26-31, Anal 29-33 → C. tamandua (Günther).

5. — Snout angle 63-82°. Snout 1.2 to 1.5 times longer than the distance of the postorbital head. Chin appendage always shorter than the eye (0.5-0.7) and inserted above the lower lip. Dorsal 32-34. → C. christyi (Boulenger)

— Snout angle 47-55°. Snout 1.5 to 2 times longer than the distance of the postorbital head. Chin appendage 0.7 to 1.4 times longer than the eye and extending directly from lower lip. Dorsal 29-30 → C. phantasticus (Pellegrin)

6. — Chin appendage approximately equal to the eye, 0.7 to 1.3 times as long as the eye. Standard length 5.7 to 8.5 times longer than the snout. → 7.

— Chin appendage 1.9 to 7.8 times longer than the eye. Standard length 5.2 to 5.7 times longer than the snout. → C. mirus (Boulenger)

7. — Standard length 5.8 to 7.3 times snout. Chin appendage non-tapered, obtuse, equal to or longer than the eye: 0.9 to 1.5 times, usually inserted above the lower lip. Body depth ranging from 3.3 to 3.8 times in standard postorbital length. Snout angle: 35 to 61°. → C. elephas (Boulenger)

— Standard length from 7 to 8.5 times snout. Chin appendage sharp and pointy, shorter, equal to, or slightly longer than (0.7 to 1.3 times) the eye, not inserted above the lower lip. Body depth ranging from 2.8 to 3.3 times postorbital standard length. Snout angle 56 to 71°. → C. alces (Boulenger)

8. — Snout less than 4 times as long as deep. Standard length from 5 to 7.2 times longer than the snout. → 9.

— Snout more than 4 times as long as deep. Standard length 2.8 to 5.3 times longer than the snout. → 10.

9. — Caudal peduncle 2.2 to 2.8 times as long as deep. Snout angle 20 to 40°. 20-22 scales around the caudal peduncle. Dorsal 27-29. Anal 30-31. More than 100 scales in longitudinal series. → C. bredoi (Poll)

— Caudal peduncle 3 to 3.4 times as long as deep. Snout angle 45-50°. 16 scales around caudal peduncle. Dorsal 31. Anal 33-35. 76-78 scales in longitudinal series. → C. cassaicus (Poll)

10. — Snout 1.6 to 2 times longer than postorbital head length, 4.4 to 6.8 times longer than deep. Eye diameter 4.6 to 8.8 times in snout. Snout angle 40-67°. → 11.

— Snout 2 to 5 times longer than postorbital head length, 5.9 to 19 times longer than deep. Eye diameter 5.7 to 19 times the snout. Snout angle 25-60° → 12.

11. — Snout angle 40-50°. Number of vertebrae 46-47, 4-5 intermediate vertebrae. Caudal peduncle 3 to 3.8 times longer than deep. → C. rhynchophorus (Boulenger)

— Snout angle 65-67°. Number of vertebrae 44-45, three intermediate vertebrae. Caudal peduncle 2.3 to 2.8 times longer than deep. → C. luapulaensis (David & Poll)

12. — Dorsal 31-32. Anal 35-36. Snout 7.5 to 19 times longer than deep. Eye diameter 6-19 times in the snout. → 13.

— Dorsal 28-30. Anal 30-34. Snout 5.9 to 9 times longer than deep. Eye diameter 5.7 to 12 times in the snout. → C. tshokwe (Poll)

13. — Distance between posterior nostril and the eye 0.4 to 1.3 times as long as the eye diameter. Eye diameter from 2 to 3.7 times in the postorbital head. Vertebrae 45 to 46. → C. numenius (Boulenger)

— Distance between posterior nostril and the eye 1.3 to 3.6 times as long as eye diameter. Eye diameter 3.1 to 6.2 times in the postorbital head. Vertebrae 49 to 50. → C. curvirostris (Boulenger)