Supplementary data for: Resolving taxonomic uncertainty in Australian sea snakes (Elapidae: Hydrophiinae): Museum evidence reassigns Australian Hydrophis caerulescens records to Hydrophis donaldi

An unverified component of Australia’s rich sea snake fauna is Hydrophis caerulescens, which is known from nine specimens collected in the Gulf of Carpentaria and provisionally identified by McDowell in 1972 based on their diagnostic high number of maxillary teeth. Micro-ct images of two paratypes of H. donaldi, which is thought to be endemic to Australia’s Gulf of Carpentaria, unexpectedly revealed a similarly high maxillary tooth count, prompting a re-assessment of both species. We examined 51 museum specimens and collated published morphological data for a further 55 individuals. Using counts of maxillary teeth, scale rows around the neck and body, temporal scale arrangement, and colour pattern, all nine Australian records previously referred to H. caerulescens, and a single juvenile from southern New Guinea, were confidently identified as H. donaldi. This expands the known range of H. donaldi from a single locality in the Gulf of Carpentaria, to include much of the fringe of the Gulf of Carpentaria as well as the top end of the Northern Territory and southern New Guinea. Hydrophis donaldi and H. caerulescens are not closest relatives; instead their striking morphological similarity appears to represent yet another example of convergence in the taxonomically challenging Hydrophis. We present external morphological characters that distinguish H. donaldi from co-occurring congeners to support field identification of this poorly known species. Our study reduces the number of confirmed Australian sea snake species from 30 to 29 and underscores the need for targeted investigations of museum specimens to resolve remaining taxonomic uncertainties.