Tip of isthmus below middle of lower eye. Scales on ocular side ctenoid, armed with a row of hairlike spines. Caudal fin with 3 simple rays on upper and lower margins respectively. Pectoral fin elongated into a filament, longer than head. Caudal fin without a dark band. In male, body on blind side stained with dark-blue except for head, interorbital width broader and pectoral fin longer than in female.