| Main Ref. | Smith, D.G., 1997 |
| Appearance refers to | |
| Bones in OsteoBase |
| Specialized organs | |
| Different appearance | always different morphology between mature adults |
| Different colors | |
| Remarks | Males undergo pronounced morphological changes at maturity: the olfactory organs enlarge, the jaws degenerate, and the teeth are reduced or lost. |
| Striking features | light organs |
| Body shape lateral | eel-like |
| Cross section | |
| Dorsal head profile | more or less straight |
| Type of eyes | |
| Type of mouth/snout | other (see diagnosis) |
| Position of mouth | |
| Type of scales | |
| Diagnosis |
Mouth greatly enlarged by a backward extension of jaws, gape comprising half or more of preanal length; buccal cavity greatly distensible. Tail attenuated and ending in an expanded, luminous caudal organ. Caudal fin absent; scales absent; lateral line without pores, instead with groups of elevated tubules. |
| Ease of Identification |
| Lateral Lines | 1 Interrupted: No |
| Scales on lateral line | 0 |
| Pored lateral line scales | 0 |
| Scales in lateral series | 0 |
| Scale rows above lateral line | 0 |
| Scale rows below lateral line | 0 |
| Scales around caudal peduncle | 0 |
| Barbels | |
| Gill clefts (sharks/rays only) | |
| Gill rakers | |
| on lower limb | |
| on upper limb | |
| total | |
| Vertebrae | |
| preanal | |
| total |
| Attributes | |
| Fins number | 1 |
| Finlets No. | Dorsal 0 - 0 |
| Ventral 0 - 0 | |
| Spines total | 0 - 0 |
| Soft-rays total | |
| Adipose fin | absent |
| Attributes | more or less truncate; confluent |
| Fins number | 1 |
| Spines total | 0 - 0 |
| Soft-rays total |
| Pectoral | Attributes |
| Spines | |
| Soft-rays | |
| Pelvics | Attributes |
| Position | |
| Spines | |
| Soft-rays |