Sea snakes are true snakes that look a little like eels because of their horizontally flattened rudder-like tails, and they spend a lot of time…for most species, their entire lives…in the ocean. Only one species seems to be able to move on land at all. They seem to all be venomous, some extremely so. They are all tropical or near-tropical, and there are numerous species distributed among about 15 genera.
One species is Enhyrina schistosa, known as the Beaked Sea Snake, or the Hook-Nosed Sea Snake. It lives in the waters near Indonesia and Australia. This is known to be the most venomous of all of the sea snakes, and a certain number of people are bitten by them. In fact, most people who die of sea snake bites were bitten by Enhyrina schistosa. How many people get bitten by them? Hard to say. In Australia, between 1942 and 1950, 56 people died from sea snake bites. What is the meaning of that number? Hard to say; it is just one of those esoteric bits of information one finds in Wikipedia. These snakes probably don’t bite very many people, but when they do, you have a problem.
As one can see the two populations, from Australia (top) and Southeast Asia (bottom), separated by numerous other species that look very different. And, if you look at just the Southeast Asian group, they cluster into two subgroups as well. Apparently this genetic divergence and grouping was not noticed by prior researcher dividing the snakes up into species and genera on the basis of morphology. Having said that, it is also true that the sea snakes are a bit dicy in their overall phylogeny, and are understudied. This, apparently, is being rectified. There are other potential explanations for this pattern that should be considered, involving the genetics. It is possible to come up with a genetic tree that inaccurately represents the actual phylogeny of the species at hand. This study, however, used multiple methods and multiple DNA sites, involving both mitochondrial and nucleic DNA, so the species tree you see here is probably reasonably close to accurate, and the conclusion that Enhydrina schistosa consists of two groups that are not monophyletic is strong.