Coral Snakes are elapids and do not have pits or a triangular heads.
Before any detail is paid to the physiological events that occur post-envenomation, it is important to examine the categories and anatomy of venomous snakes. Venomous snakes are not always easily identifiable, but there are several characteristic qualities that these reptiles tend to share. The first and most important quality is triangular head shape as nearly all poisonous snakes have venom glands that make the head more triangular than oval. This is not a guarantee, however, as is exemplified by the coral snake at the top of the page. Elapids tend to have oval shaped heads. If a second set of pits can be identified on the snakes face, below the nostril, it is a poisonous snake and should be avoided. Many venomous snakes have vertical pupils, and any snake with such slit-like pupils should not be poked or played with. The scale pattern of the tail is also different between venomous and non-venomous snakes, and the presence of a rattle is always a guarantee that the snake is venomous. If you are lucky (or unlucky, depending on how you see things) enough to see a snake in the ocean, it is venomous. Sea snakes are the most lethal of all known venomous snakes, but fortunately are not aggressive and rarely bite humans.
Left: Vertical Pupils and Triangle Shaped Heads are Indicators that a Snake is Venomous. Right: The heat sensitive pit is clearly visible in this picture of a crotalid. Photos by Mardi Snipes.
There are four major groupings of venom producing snakes. These four are: Crotalidae (pit vipers, named so for the heat sensitive pits that are used for seeking prey), Elapidae (elapids), Viperidae (vipers), and Hydrophids (sea snakes).
Structural differences in venomous and non-venomous snakes are obvious when skulls are compared. The top right image is of a non-venomous python (note the lack of any fangs). Image taken from Snake Venom Poisoning, copyright 1983. Scholium International, Inc.
Crotalids, also known as pit vipers, are highly evolved, have heat sensing depressions (pits) near the nostril, and have the most complex venoms of all snakes. They are usually considered by herpetologists to be the most highly evolved of the poisonous snake categories. Elapids are often difficult to recognize as poisonous snakes because they often lack the common triangle shape head. Mambas, and cobras are elapids, and while their venoms are very toxic and often fatal, it is the least complex of the four categories of poisonous snakes. These snakes are sometimes considered to be the least evolved, but there are disagreeing factions. Viperids are any of the non-pitted vipers, and hydrophids are sea snakes, which are very poisonous and have a characteristic flattened tail that functions much like a fin for swimming. Proteroglyphs have non-retractable anterior fangs (elapids and sea snakes) while solenoglyphs have retractable fangs (vipers and pit-vipers).
A pelagic sea snake. Notice the flattened tail. Image from the Smithsonian Institute.
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