Body stout without markings. Scales large and shiny; scales of the lateral line with ramified tubes (M. atlanticus 2). One dorsal fin with a short base but with a long filament. Base of the anal fin longer. Origin of pectoral fins very low. Mouth upturned.
Inhabit coastal waters, bays, estuaries, mangrove-lined lagoons and rivers, to a depth of 30 m (M. atlanticus). Often found in river mouth and bays, with entering fresh water. Large schools may inhabit a particular area for years. Feed on fish and crabs. The swim bladder can be filled directly with air, permitting the fish to live in oxygen poor waters.
Occasional Florida, Bahamas and Caribbean.
The large scales are used in ornamental work and in preparation of artificial pearls.