Clingfishes and Singleslits: Gobiesocoidei

Instead of pelvic fins, or the pair that corresponds to the rear legs of four-footed animals, clingfishes have a sucking disk they use to cling to rocks, plants, and even sea urchins. Most clingfishes have a tadpole-shaped body, but one species has a long, thin body that mimics the long spines of a sea urchin. Clingfishes have no scales but shield themselves with mucus. They also have no swim bladder, an internal sac that fishes use to control their position in the water. The colors of clingfishes vary from black to orange, brown, green, or red. The fishes also may have stripes, bars, or spots of yellow, blue, green, brown, gray, or white. Most clingfishes are about 2 inches (5 centimeters) long, but some reach a length of 12 inches (30 centimeters). Clingfishes have one dorsal and one anal fin. The dorsal (DOOR-suhl) fin is the one along the midline of the back. The anal (AY-nuhl) fin is the one along the midline of the belly.

Singleslits have an eel-like shape. The pelvic fins are very small. These fishes have a sucking disk, but it does not function. The dorsal and anal fins look like those of eels. Only the tail fin has rays, or supporting rods. The colors vary from frosty pink or green to light green, brown, gray, or black. Spots or bars of black, gray, brown, or yellow may be present. Singleslits are usually smaller than 2 inches (5 centimeters) long, but one species reaches a length of 5 inches (12 centimeters).