An in-depth study of the loach species Homaloptera orthogoniata has turned up a new species found only in the waters of Thailand and Peninsular Malaysia.
Heok Hui Tan and Peter Ng studied a large number of balitorine loaches in museum collections that had been previously identified as Homaloptera orthogoniata, and found that they were distributed across Thailand, Peninsular Malaysia, Sarawak, Kalimantan Timur and Kalimantan Barat.
However, close analysis of this stunning loach species revealed that some of them were actually a different species, and that the true H. orthogoniata was in fact confined to Borneo and wasn't as widespread as previously believed.
H. parclitella from the Malay Peninsula differs from the Borneo orthogoniata in the presence of two dark brown saddles on the dorsal surface, rather than the three usually seen in orthogoniata.
It seems probable that some of the orthogoniata on sale in the shops, and seen in books, may have been the new fish, H. parclitella, which is found over a wider area and in places better known for their fish exports.
Another species, Homaloptera confuzona, described by Maurice Kottelat in 2002, is also incorrectly sold under this name and has been sold in some UK stores in the past under this name. Rather than the distinct saddles seen in orthogoniata and parclitella, confuza has an irregular pattern on its dorsal surface.
The new loach also has higher scale counts for the lateral line series, the predorsal series and caudal peduncle scales. Tan and Ng have also redescribed orthogoniata from the type and from fresh material to help clarify the situation.
For more details on the new species of loach see the paper: Tan, HH and Ng, PKL (2005) - Homaloptera parclitella, a new species of torrent loach from the Malay Peninsula, with redescription of H. orthogoniata (Teleostei: Balitoridae). Ichthyological Exploration of Freshwaters, Vol. 16. No. 1-12.