Mainly marine; some species enter freshwater.
Distribution: Indo-West Pacific; one species entered the Mediterranean through the Suez canal. Strongly compressed, slimy body.
Scales small. Head naked, bearing bony ridges on upper surface.
Gill membranes united with isthmus.
Mouth small and very protractile.
No teeth on palate.
Pseudobranchiae absent. Dorsal fin continuous with 8 or 9 spines that are somewhat elevated, in the anterior portion; posterior portion with 14-16 soft rays. Three spines on anal fin.
Dorsal and anal fin spines with a locking mechanism. A scaly sheath at the base of dorsal and anal fins. Vertebrae 22-23.
All species have esophageal luminous organs.
Also noted for their production of mucus (see common name).
Common in shallow coastal waters and tidal creeks where they feed on benthic invertebrates. Easily caught by trawls or beach seines; important artisanal food fish.