Now this is what I call keeping a common name simple and, yes, there is a second Brachydiplax species, B. duivenbodei, which is tagged a Darkmouth. B. denticauda is native to Australia, Indonesia, PNG and the Solomon Islands.
I had just a single encounter with this species at the the St. Lawrence Wetlands in Queensland, 2019. In my 2022 FNQ trip, I saw it more frequently and just about snagged a 3-winged female.
Males are typical of other Brachydiplax species with the mature male being powder blue. The palemouth name looks appropriate. Brachydiplax duivenbodei (Darkmouth) could be confused but its mature males, which we found in FNQ 2022, do not show the black abdomen tip.