Thrissina invicta sp. nov. is described based on 46 specimens collected from Philippine Islands. The new species is morphologically most similar to Thrissina katana Hata, Lavoué and Motomura 2022, Thrissina malabarica (Bloch 1795), and Thrissina mystica Hata, Lavoué and Motomura 2025, three species previously included in “Thryssa hamiltonii.” However, Thrissina invicta sp. nov. differs from these species by several morphological metrics including higher counts of gill rakers and lower counts of vertebrae, as well as both a longer head and a deeper body. The new species is most likely to be the sister taxon to T. katana due to their close morphological similarity based on preserved specimens in museums, but this is yet to be confirmed by genetic analysis. If they are sister taxa, their divergence may have resulted from allopatric speciation during the long isolation of shelf areas around the Philippine Islands from those around Sundaland (now the islands of Southeast Asia, Indonesia and Malaysia) during Pleistocene era intervals of low sea levels associated with glacial maxima. The current overlapping distribution of Thrissina invicta sp. nov. and T. katana off Palawan Island is interpreted as a secondary contact zone, highlighting the influence of both Philippine Islands and Sundaland in the assembling of the marine ichthyofauna of this island.
Actinopterygii, Clupeomorpha, taxonomy, Thrissina katana, Thryssa hamiltonii
