First described as recently as 1998 (2), Brachycephalus pernix is a minute amphibian, barely a centimetre or so in length, with short, robust limbs, a relatively large, rounded head, and a short snout. The body is orange, with black blotches on the flanks and limbs, and the eyes are black (2) (3). The extent of black colouration on the body may vary between individuals, but the basic pattern of orange and black is characteristic and helps distinguish the species from the similar Brachycephalus ephippium, which is uniform orange, and Brachycephalus nodoterga, which is grey (2). Brachycephalus pernix is also distinguished by the absence of a bony shield above the backbone (2) (3), a characteristic of other Brachycephalidae species (4) (5). The head, back and underside of the body are smooth, and the surfaces of the flanks are wrinkled, but, unlike B. nodoterga, the body lacks warts (2). Like other members of the group, Brachycephalus pernix has a reduced number of digits on the hands and feet (5), and the species is also distinguished by the absence of any external trace of the fifth toe (2) (3).
- Male snout-vent length: 12 - 13.3 mm (2)
- Female snout-vent length: 14.1 - 15.8 mm (2)