Abstract
The shallow water planktonic shrimp Acetes indicus H. Milne Edwards, 1830 (Crustacea: Decapoda: Sergestoidea) was established on the basis of specimens obtained from the Ganges Delta, and is the type species of the genus Acetes. This shrimp is important as one of the major products for small-scale coastal fisheries across tropical eastern Asia. The results of mitochondrial DNA analyses from individuals across South and South-East Asia have revealed the existence of two genetically separate major clades, one of which could be further divided into two sub-clades, leading to three reciprocally monophyletic clades (Bangladesh, South-East Asia, and eastern Indian Ocean clades). Morphological analysis agreed with the results of genetic analyses by showing minor, but consistent differences between the three clades, demonstrating that they are isolated reproductive units. This finding has raised a concern about the true identity of A. indicus. The type (s) of A. indicus were not found in the most possible holding institution, Muséum national d’Histoire naturelle, Paris (MHHN). Specimens from Bangladesh, possible topotypic materials sampled at different times and locations, were regarded the representative of A. indicus. Accordingly, a new species, Acetes omorii (≈ Omori’s large form), is proposed to accommodate the sister clade occurring in South-East Asia. Moreover, Acetes spiniger Hansen, 1919, once regarded a synonym of A. indicus, is herein re-validated to accommodate the Indian Ocean population (≈ Omori’s small form).
