| Main Ref. | Whitehead, P.J.P., 1985 |
| Appearance refers to | |
| Bones in OsteoBase |
| Specialized organs | no special organs |
| Different appearance | males alike females |
| Different colors | males alike females |
| Remarks |
| Striking features | striking fins |
| Body shape lateral | fusiform / normal |
| Cross section | compressed |
| Dorsal head profile | more or less straight |
| Type of eyes | more or less normal |
| Type of mouth/snout | more or less normal |
| Position of mouth | terminal |
| Type of scales | cycloid scales |
| Diagnosis |
The filamentous last dorsal fin ray distinguishes this species from members of any other eastern Pacific clupeoid genus. Lower gill rakers 50 to 87 in fishes over 14 cm standard length (intermediate between O. medirastre with 41 to 69 and O. libertate with 63 to 110, but neither of these occur in the Galapagos Islands). |
| Ease of Identification |
| Lateral Lines | Interrupted: No |
| Scales on lateral line | |
| Pored lateral line scales | |
| Scales in lateral series | |
| Scale rows above lateral line | |
| Scale rows below lateral line | |
| Scales around caudal peduncle | |
| Barbels | 0 |
| Gill clefts (sharks/rays only) | |
| Gill rakers | |
| on lower limb | 50 - 87 |
| on upper limb | |
| total | |
| Vertebrae | |
| preanal | |
| total |
| Attributes | last fin rays very elongated |
| Fins number | 1 |
| Finlets No. | Dorsal 0 - 0 |
| Ventral 0 - 0 | |
| Spines total | 0 - 0 |
| Soft-rays total | 13 - 21 |
| Adipose fin | absent |
| Attributes | forked; more or less normal |
| Fins number | 1 |
| Spines total | 0 - 0 |
| Soft-rays total | 15 - 17 |
| Pectoral | Attributes more or less normal |
| Spines 0 | |
| Soft-rays | |
| Pelvics | Attributes more or less normal |
| Position abdominal behind origin of D1 | |
| Spines | |
| Soft-rays 7 - 10 |