The first Brachycephalus pulex specimens were found between December 2009 and July 2010 in the Serra Bonita mountain range in the Camacan and Pau Brasil municipalities of Bahia, Brazil.

[5] This is in contrast to the bufoniform body plan of the pumpkin toadlets within the genus Brachycephalus, which have poorly-developed hind limbs and wider heads.

Its describers noted this behavior when observing individuals in natura, when one specimen feigned death after jumping several times and landing on a leaf.

[8][9] The skeletal structure of Brachycephalus pulex is nonhyperossified, meaning that the skull bones and spinal processes of the sacral and presacral vertebral lack sculpturing.

[10] The miniature size of Brachycephalus pulex is notable; one adult specimen had a snout–vent length of 6.45 millimetres (0.254 in).

[11] The second smallest vertebrate is also a species in the Brachycephalus genus, B. dacnis, with a minimum length of 6.95 millimetres (0.274 in).

The IUCN listed urban expansion, agriculture, and livestock grazing as the leading causes for habitat loss—and thus declining populations—in this species.

The relationships of this clade in relation to other frog families are shown in the cladogram below:[15] Rana catesbeiana Agalychnis callidryas Litoria caerulea Phyzelaphryninae Eleutherodactylinae Brachycephalus Ischnocnema Craugastoridae Holoadeninae Strabomantinae In 2020, Condez, Haddad & Zamudio tested the phylogenetic relationships of Brachycephalus species.

They recovered Brachycephalus pulex as the basalmost member of the genus, as the sister taxon to all other species.