The river martins form a distinctive subfamily Pseudochelidoninae within the swallow and martin bird family Hirundinidae. The two species are the African river martin Pseudochelidon eurystomina, found in the Congo and Gabon, and the white-eyed river martin Pseudochelidon sirintarae, known only from one site in Thailand. These are medium-sized, largely black swallows that have a light buoyant flight and feed on insects caught in the air. They appear to be more terrestrial than other swallows, frequently walking rather than perching, and the white-eyed may be crepuscular. The African species excavates nest holes in sandy ridges in rivers, while the breeding locations and habits of the Asian bird are unknown.
When the African river martin was first discovered in the 19th century, Gustav Hartlaub thought it was a roller, and later authors either placed it in its own family, or with the woodswallows. Study of the anatomy revealed that the species was closest to the swallows and martins, but that it possessed a number of distinctive features, such as its robust legs and feet and stout bill. These indicated that it should be placed in a separate subfamily. The two river martin species are usually considered to belong to a single genus, Pseudochelidon, due to their having a number of structural similarities. However, Brooke proposed that the white-eyed river martin be placed in a separate monotypic genus Eurochelidon.
The African river martin has a restricted distribution; it appears to be locally numerous, although its true status has not been fully investigated. The white-eyed river martin was discovered as recently as 1969 and is only known from specimens and anecdotal evidence – no modern ornithologists have seen the species in the wild, and its breeding grounds are unknown. It may be extinct, although a possible sighting was reported in 2004.
The two members of the subfamily have geographically separate ranges. The African river martin breeds along the Congo and Ubangi rivers in the Democratic Republic of the Congo. It is migratory, wintering in coastal savannah in southern Gabon and the Republic of Congo; it has recently been discovered to nest in beach ridges and grassland in its coastal wintering areas. The white-eyed river martin is known only from its wintering site at Bueng Boraphet lake in Thailand, where it was seen between the months of November and February. It may be migratory, but its breeding grounds and habitat are unknown, although river valleys in Northern Thailand or south-western China are possibilities, as are Cambodia and Myanmar. However, doubts have been cast on whether it is actually migratory at all.
The African species' breeding habitat consists of forested rivers with islands with sandy shores for breeding. The nesting grounds of the white-eyed river martin are unknown, but if the breeding habitat resembles that of its relative, it is likely to be the forested valleys of large rivers, which can provide sandbars and islands for nesting, and woodland over which the birds can catch insect prey. The African river martin uses coastal savannah as its winter habitat. Based on its only known wintering site, the non-breeding habitat of the white-eyed is assumed to be in the vicinity of open fresh water for feeding, with reed-beds for the night-time roost.