The lethal beaked sea snake (Enhydrina shistosa) is actually two species of identical-looking snakes which have evolved separately.
The Australian and Asian beaked sea snakes were thought to be from the same species but DNA analysis revealed that despite looking the same, the two snakes are genetically unrelated.
The mix-up could have had serious consequences as sea snake antivenom is made from the venom from the Asian beaked sea snake, on the assumption it was the same as the Australian variety. Luckily, the antivenom also happens to be effective against the Australian beaked sea snake, but it might not have been.
Read more at The University of Queensland