Type locality is ‘Central Sumatra, Indonesia’, with additional records existing from Cambodia (Mekong drainage), Peninsular Malaysia (Perak River), Sumatra (from the Siak River, Riau province to the Musi River, South Sumatra (Sumatera Selatan) province) and Borneo (south and westwards from the Belait river basin in Brunei Darussalam to the Sambas drainage in West Kalimantan (Kalimantan Barat) province, Indonesia and probably in Sarawak, Malaysia).

Type locality is given as ‘Lake Meninju, Sumatra, Indonesia’, currently known as Danau (lake) Maninjau, but conceivably the fish may have been obtained from the outflowing Antokan river rather on its western side than the lake itself.

Native to parts of southern Borneo, eastern Sumatra, Singapore, and the Malay Peninsula. In Singapore it’s considered highly-endangered and is now restricted to the Central Catchment nature reserve.

Type locality is ‘Tuluk and Gunung Sahilan, Sumatra, Indonesia’ which appears to correspond to localities within the Kampar River drainage of which the former is now known as Teluk Meranti and is o…

The type series was purchased from a market in Jambi province, eastern Sumatra, Indonesia and this species is also known from neighbouring Riau province plus the island province of Bangka. On Sumatra it may be restricted to the Indragiri and Batang Hari river systems.

Inhabits peat swamp forests and associated black water streams in which the water is typically stained brown with humic acids and other chemicals released by decaying organic material. The dissolved mineral content is generally negligible and the pH can be as…

N. selangoricus is most similar to N. spiniferus since it possesses acuminate scales above and below the lateral line on the caudal peduncle, a feature not shared with any other congener. It can however be distinguished by the following characters: presence of 8-12 very regular dark bars on flanks (vs. 10-13 irregularly-shaped bars in N. spiniferus), 3-5 times…

The easiest way to distinguish these is by examining the throat markings, which vary according to species, and in the case of B. hipposideros form a black horse-shoe shape. It can also be separated from other group members by the following suite of characters: dark blotch on throat joined to black lower lip; presence of transverse bars in dorsal and caudal fins; absence of dark margin in anal-fin; opercle usually with gold scales, without iridescrent green scales; ventral margin of opercle brown; 6.5-7 subdorsal scales (mode 6.5); 9-10 postdorsal scales (mode 9.5); 31-32 lateral scales (mode 32).

This species is included in the Betta waseri group/complex of closely-related species within the genus, an assemblage which also includes a handful of unidentified fishes such as B. sp. ‘Medas’ on an unofficial basis. Group members share the following combination of characters: base body colouration clay yellow; opercle scales iridescent gold in mature males of all species except …

This species is the only member of the B. edithae group within the genus, and separated from all other Betta spp. by the fact that the branchiostegal membrane and posterior portion of the opercle are opaque or translucent.

The original diagnosis by Vierke also states that it has relatively small eyes and short fins with a typical pattern of partial barring.

Fowler (1940) described this species as the unique member of his new genus Homalopterula on the basis of a single specimen, separated from related genera by the curved shape of the jaws, truncate caudal-fin and scaleless ventral surface.

This species is traded under various names including 'chocolate scissor-tailed loach', chocolate long-finned loach', 'red line cobra loach', 'spiny eel loach' and 'dragon loach'. It's apparently difficult to find in its natural habitats and thus time-consuming to collect, meaning it's rarely traded in numbers, sought after by enthusiasts and tends to carry a relatively high price tag when available.

The genus currently contains just three…