Type locality is ‘ Kapa, northwestern peninsular Thailand’, which may refer to modern-day Kapoe district, Ranong province, and additional records exist from other localities in Ranong as well as Phang-nga and Pattani provinces.

Although the precise extent of its distribution is unclear it appears to occur in river systems on both sides of the Tennaserim Hills in pen…

The water at the type locality is described as ‘clear and fast-flowing over a rocky substratum’. H. parclitella was observed in shallow water among the rocks, and sympatric species included Garra cambodgiensis, Neolissochilus soroides, Poropuntius smedleyi, ‘Puntius‘ binotatus, Homaloptera nebulosa and Amblyceps mangois.

The anatomical structure of miniaturised cyprinids can vary greatly, and there are two principle ‘groupings’ with some species possessing intermediate features to some degree. The first contains those fishes which though small are essentially proportionally dwarfed versions of their larger relatives, e.g., Barboides, Microdevario, Microrasbora, Horadandia, Boraras, Sawbwa, Sundadanio, Danio, Laubuca and Rasbora.

The other includes those in which anatom…