Order names linked to a common name example.
| 1 | a. Caudal fin heterocercal b. Caudal fin not heterocercal |
2 4 |
| 2 | a. Caudal fin strongly heterocercal; mouth inferior; jaws almost or entirely toothless b. Caudal fin abbreviated heterocercal, rounded behind; mouth terminal and bearing strong teeth |
Acipenseriformes 3 |
| 3 | a. Scales ganoid; dorsal fin short b. Scales cycloid; dorsal fin long |
Lepisosteiformes Amiiformes |
| 4 | a. Skull asymmetrical, both eyes on same side of head b. Skull symmetrical, eyes, if present, on opposite sides |
Pleuronectiformes 5 |
| 5 | a. Dorsal, caudal, and anal fins continuous b. Dorsal, caudal, and anal fins separate |
Anguilliformes 6 |
| 6 | a. Body completely covered with dermal plates; snout elengated, tubular; anal fin redimentary or absent b. Body scales or naked, never with dermal plates; snout never tubelike; anal fin present |
Syngnathiformes 7 |
| 7 | a. Body scaled or naked, but not with plates; head naked b. Body scaled, or if naked, with few to many bony plates; head usually scaled |
Cypriniformes 8 |
| 8 | a. Spines in fins completely absent b. Spines present in at least some fins (spines may be flexible or stiff, but not segmented) |
9 12 |
| 9 | a. Barbels absent b. A single median chin barbel present |
10 Gadiformes |
| 10 | a. Pectoral fins placed high on the sides, above the axis of the body b. Pectoral fins placed near or much below the body axis |
Beloniformes 11 |
| 11 | a. Maxillae not forming border of upper jaw; jaw teeth conical in bands b. Maxillae form part of the border of upper jaw; jaw teeth, if present, conical and never in bands |
Cyprinodontiformes Clupeiformes |
| 12 | a. Dorsal fin preceded by free spines (not connected by membranes) b. Dorsal spines connected by membranes, to each other or to the soft dorsal fin |
Gasterosteiformes 13 |
| 13 | a. Pelvic fins abdominal or subabdominal; pectoral fins high on the sides, usually above body axis b. Pelvic fins thoracic or nearly so; pectoral fins usually below body axis |
Mugiliformes 14 |
| 14 | a. Adipose fin present, or, if absent, the anus is far forward in the region of the isthmus b. Adipose fin absent; anus in usual position just in front of anal fin |
Percopsiformes Perciformes |
Order names and common name example: