Yom River, Saerabhumi, Roi Et Province, Thailand, 85.6mm., 2013/iii/07
Hyriopsis bialata is a freshwater mussel with an extraordinary shape from a raised keel in the posterior half of the shell, which varies in extent greatly between individuals with some completely lacking it. It is native to southeast Asia from Thailand to Cambodia; and is a filter-feeding bivalve inhabiting sandy bottoms of river streams. It is an economically important species locally especially in Thailand, with the nacreous shell and pearl produced being used in various kinds of jewelry and ornament making and the meat being used for food or livestock feed. Although a common species, human-induced environmental degradation is causing population in Thailand to decline rapidly in the recent years. It is one of the most fecund (fast generation time, spawning throughout the year) unionids native to the area and aquaculture of this species exist in Thailand. Typical shell length around 80mm., extremely large specimens may approach even 130mm.