| 1a. | Body globular, usually covered with tubercles; one or two short dorsal fins never confluent with caudal | Family Cyclopteridae Lumpfishes |
| 1b. | Body elongate | 2 |
| 2a. | Two dorsal fins, the first spinous and the second of soft-rays | |
| 2b. | One dorsal fin | 3 |
| 3a. | Gill membranes united but free from isthmus; dorsal fin far back, covering less than 1/2 of dorsal surface | Family Gobiesocidae Clingfishes |
| 3b. | Gill membranes joined to isthmus; dorsal fin covering over 1/2 of dorsal surface, may be confluent with caudal | Family Liparidae Snailfishes |