The Río Calchaquí rises at almost 6000 m AMSL and flows swiftly through a mountainous valley where it is largely fed by snow melt. The climate is semi-arid and cool with an air temperature of 12-18°C, while rainfall is largely concentrated during summer when the flow can be torrential. The water is hard and rich in salts, with pH measured at 8.04 during the month of August. Aquatic vegetation and filamentous algae grow around the margins and in tributaries.

It can be distinguished from the majority of other Corydoras species by its distinctive colour pattern, comprising a uniform, lightish base pigmentation with a dark arched stripe extending over the upper portion of each flank, from the tip of the snout to the caudal-fin base. This is shared with a few congeners, however, including C. arcuatus, C. narcissus, and C. urucu.

Endemic to northern and central Borneo, with records from the Malaysian states of Sarawak and Sabah, Brunei Darussalam, and the Indonesian provinces North Kalimantan (Kalimantan Utara) and East Kalimantan (Kalimantan Timur).

Type locality is ‘Kajan River, eastern slope of central Kalimantan, Indonesia [Borneo]’.

Nematabramis species are found a variety of habitat-types, from swiftly-flowing affluent streams to pools, lakes, and degraded swamps. Based on the available collection records juveniles and subadults of N. everetti display a preference for fast-moving water whereas adults are found in deeper, slower stretches of minor tributaries.

It looks particularly similar to N. alestes with both species possessing a colour pattern comprising a dark lateral stripe on the body, but can be distinguished immediately by possessing barbels longer than the head (vs. shorter than the head in N. alestes).

N. alestes is the only member of the genus in which the barbels are shorter than the head, with additional diagnostic characters as follows: 8-9 branched dorsal-fin rays; 12-14 branched anal-fin rays; 22-23 predorsal scales; body with a pronounced ventral keel.

This species can be distinguished from congeners by the following combination of characters: body relatively slender, depth fitting 3.4-3.8 times in SL; 32-33 + 2 lateral line scales; 14 circumpeduncular scale rows; presence of a single pair of barbels; black distal margin on dorsal-fin; numerous body scales with dark, crescent-shaped markings.

Known from the middle Mekong basin in Laos and Thailand, and may be endemic to the Khorat Plateau. Records exist from the Mun and Songkhram watersheds in northeastern Thailand, and a number of Mekong tributaries in laos, including the Nam Mang and Nam Kou drainages.

Type locality is ‘Nam Mang downstream of Ban Thabok, between 18°22’25″N, 103°13’30″E, and about 1 kilometer upstream, Vientiane Province, Laos’.

Known from the middle Mekong basin in Laos and Thailand, including the Mun tributary drainage on the Khorat Plateau in northeastern Thailand, plus the Chao Phraya and Mae Klong watersheds in central and western Thailand, respectively. In the Mekong system it may also occur further upriver in Yunnan province, China, while the Khone Falls in Laos appear to represent its downstream limit.

This species can be distinguished from congeners by the following combination of characters: body depth fits 2.5-2.7 times in SL; 28-31 +2-3 lateral line scales; 14-16 circumpeduncular scale rows; 5-5½ scale rows between the lateral line and dorsal-fin origin; a triangular distal blotch on the dorsal-fin; a few body scales with crescent-shaped black edges; a thin dark margin on the dorsal-fin, posterior to the distal blotch; a dark posterior margin on the caudal-fin; normally a single pair of rudimentary barbels present.