From Amazonas and Pará (Brazil) westward along the Amazon through northern Peru and eastern Ecuador, southern and east-central Colombia throughout the Amazon watershed and north as far as Villavicencio along the Orinocoan drainage of the eastern Andes.
Holotype: BMNH 1946.1.20.13 (formerly BMNH 1851.12.26.15); number not stated in original description.
Type-locality: Pará, Brazil
Two subspecies, namely M. f. filiformis (Gunther, 1859) and M. f. subtilis Roze, 1967, were recognized by Roze, 1983 [dated 1982], Mem. Inst. Butantan 46:305-338[322-323], the most recent reviewer. However, Cunha and Nascimento, 1982, Bol. Mus. Para. Emilio Goeldi, Ser. Zool. 112:1-59[1], did not recognize subspecies.
