Phylogeography and distribution of the freshwater razor clams Novaculina myanmarensis and N. gangetica in Myanmar, with notes on two doubtful nominal taxa described as Novaculina members (Bivalvia: Pharidae)

The razor clam genus Novaculina Benson, 1830 (Bivalvia: Pharidae: Pharellinae) is a group of secondary freshwater bivalves. Four allopatric species in this genus are distributed throughout Asian freshwater drainages from the Ganges River in India to the Yangtze River in China. Here, we present several new occurrences of Novaculina myanmarensis and N. gangetica from Myanmar that were confirmed by means of a molecular approach. These occurrences expand our knowledge on the ranges of both species. Furthermore, we compiled an updated distribution map for all the species in this genus. Our phylogeographic research suggests that Novaculina myanmarensis colonized the Ayeyarwady Basin from rivers of the Salween Estuary (Donthami and Ataran rivers) during the Late Pleistocene. Conversely, Novaculina gangetica populations from Myanmar does not demonstrate any clear phylogeographic structure. At first glance, this pattern can also be caused by a (sub)recent (Pleistocene) immigration into coastal rivers of western Myanmar from the Ganges Basin, although this preliminary hypothesis is yet to be confirmed using DNA sequences of samples from India and Bangladesh. Finally, the taxonomic status of two doubtful nominal taxa initially described as Novaculina members is discussed, i.e. N. gangetica theobaldi Hanley & Theobald, 1874 and N. andamanensis Preston, 1908. These taxa are considered junior subjective synonyms of the estuarine bivalve species Cultellus maximus (Gmelin, 1791) (Pharidae) and Azorinus coarctatus (Gmelin, 1791) (Solecurtidae), respectively.