Betta falx Tan & Kottelat 1998

This species is closely related to Betta picta from Java where it can be distinguished in the following characters: fewer dorsal fin rays (mode 8 vs. 9); fewer lateral scales (mode 27 vs. 28); dorsal fin origin above 11-12th lateral scale (vs. 12-14th); anal fin origin below modal 6th lateral scale (vs. 7th); fewer predorsal scales (mode 19 vs. 20); slightly greater anal-fin base length (46.5-50.3% SL vs. 42.6-48.4); anal and caudal fins with reddish distal band in live male (vs. bluish); iridescent greenish-blue opercle scales (vs. yellow-gold); in preserved specimens, male with distinct dorsal transverse bars (vs. faint); male with distinct dark anal distal margin wide (vs. narrow); male without elongated median caudal fin rays (vs. presence); female with distinct caudal transverse bars (vs. very faint or absent); dorsal head view narrow (vs. broad); thick preorbital black stripe (vs. narrow); and the distance between posterior part of anal fin to lower part of caudal narrow (vs. wide) (Ref. 56386).

Dorsal spines (total): 1 - 2; Dorsal soft rays (total): 7 - 8; Analspines: 2; Analsoft rays: 19 - 21

Typically found among submerged bank vegetation, in near stagnant waters, with pH 4.7-6.8. Latin word falx means scythe, alluding to the continuous curved shape of the broad anal and caudal distal margins of a male in display. Caudal fin rounded.