Tetragonuridae
by R L. Haedrich
Medium-sized fishes with an elongate body, rounded in cross-section; caudal peduncle long and thick, square in cross-section, with modified scales forming 2 prominent low keels on each side. Eye and mouth fairly large. Two dorsal fins, the first with numerous short spines that fold into a groove; the second dorsal and anal fins similar in shape and size, the bases shorter than the base of the first dorsal, rays almost twice the length of the first dorsal spines; a single spine precedes the rays of the anal fin; pectoral fins moderately short and rounded. Scales moderate in size, with heavy longitudinal keels, firmly attached, the rows forming a pronounced geodesic pattern around the body; very small scales extending slightly onto the bases of the median fins; lateral line slightly arched anteriorly, straightening out over the end of the pectoral fin and running along the midlateral line of the body to the peduncle; tubed scales absent. Skin thick, with tiny pores; top of head and snout naked. Colour brown or blackish.
Oceanic fishes of warm and temperate waters. Most are taken singly far out at sea or occasionally stranded on shores near deep water. The juveniles commonly live within the body cavity of pelagic tunicates.
Genera 1.
Recent revision: Grey (1955)