Hydrophis peronii, commonly known as the horned sea snake, Peron's sea snake, and the spiny-headed seasnake, is a species of venomous snake in the subfamily Hydrophiinae of the family Elapidae. The species is endemic to the western tropical Pacific Ocean. It is the only sea snake with spines on the head. It is sometimes placed in its own genus Acalyptophis.

Venomous snakes are species of the suborder Serpentes that are capable of producing venom, which they use for killing prey, for defense, and to assist with digestion of their prey. The venom is typically delivered by injection using hollow or grooved fangs, although some venomous snakes lack well-developed fangs. Common venomous snakes include the families Elapidae, Viperidae, Atractaspididae, and some of the Colubridae. The toxicity of venom is mainly indicated by murine LD50, while multiple factors are considered to judge the potential danger to humans. Other important factors for risk assessment include the likelihood that a snake will bite, the quantity of venom delivered with the bite, the efficiency of the delivery mechanism, and the location of a bite on the body of the victim. Snake venom may have both neurotoxic and hemotoxic properties. There are about 600 venomous snake species in the world.