Moray eels or Muraenidae are a family of cosmopolitan eels. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water, and a few, for example the freshwater moray (Gymnothorax polyuranodon), can sometimes be found in fresh water.
The smallest moray is likely Snyder's moray (Anarchias leucurus), which attains a maximum length of 11.5 cm (4.5 in), while the longest species, the slender giant moray (Strophidon sathete) reaches up to 4 m (13 ft). The largest in terms of total mass is the giant moray (Gymnothorax javanicus), which reaches 3 m (9.8 ft) in length and 30 kg (66 lb) in weight.The majority of adult Hydrophiinae species grow to between 120 and 150 cm (3.9 and 4.9 ft) in length, with the largest, Hydrophis spiralis, reaching a maximum of 3 m (9.8 ft).Their eyes are relatively small with a round pupil and most have nostrils located dorsally.The skulls do not differ significantly from those of terrestrial elapids, although the dentition is relatively primitive with short fangs and (with the exception of Emydocephalus) as many as 18 smaller teeth behind them on the maxilla.Yellow-lipped sea krait, Laticauda colubrina
Most Hydrophiinae are completely aquatic and have adapted to their environments in many ways, the most characteristic of which is a paddle-like tail that has improved their swimming ability. To a varying degree, the bodies of many species are laterally compressed, especially in the pelagic species. This has often caused the ventral scales to become reduced in size, even difficult to distinguish from the adjoining scales. Their lack of ventral scales means they have become virtually helpless on land, but as they live out their entire lifecycles at sea, they have no need to leave the water.The only genus that has retained the enlarged ventral scales is the sea kraits, Laticauda, with only five species. These snakes are considered to be more primitive, as they still spend much of their time on land, where their ventral scales afford them the necessary grip. Laticauda species are also the only sea snakes with internasal scales, i.e., their nostrils are not located dorsally.Since it is easier for a snake's tongue to fulfill its olfactory function under water, its action is short compared to that of terrestrial snake species. Only the forked tips protrude from the mouth through a divided notch in the middle of the rostral scale. The nostrils have valves consisting of a specialized spongy tissue to exclude water, and the windpipe can be drawn up to where the short nasal passage opens into the roof of the mouth. This is an important adaptation for an animal that must surface to breathe, but may have its head partially submerged when doing so. The lung has become very large and extends almost the entire length of the body, although the rear portion is thought to have developed to aid buoyancy rather than to exchange gases. The extended lung possibly also serves to store air for dives.
Most species of the Hydrophiinae are able to respire through the top of their skin. This is unusual for reptiles, because their skin is thick and scaly, but experiments with the black-and-yellow sea snake, Pelamis platura (a pelagic species), have shown this species can satisfy about 25% of its oxygen requirements in this manner, which allows for prolonged dives Blue-lipped sea krait, Laticauda laticaudata Like other land animals that have adapted to life in a marine environment, sea snakes ingest considerably more salt than their terrestrial relatives through their diets, and when seawater is inadvertently swallowed. This meant they had to evolve a more effective means of regulating the salt concentration of their blood. In sea snakes, the posterior sublingual glands, located under and around the tongue sheath, evolved to allow them to expel salt with their tongue action Scalation among sea snakes is highly variable. As opposed to terrestrial snake species that have imbricate scales to protect against abrasion, the scales of most pelagic sea snakes do not overlap. Reef-dwelling species, such as Aipysurus, do have imbricate scales to protect against the sharp coral. The scales themselves may be smooth, keeled, spiny, or granular, the latter often looking like warts. Pelamis has body scales that are "peg-like", while those on its tail are juxtaposed hexagonal plates.The Hydrophiinae, also known as coral reef snakes or sea snakes, are a subfamily of venomous elapid snakes that inhabit marine environments for most or all of their lives. Most are extensively adapted to a fully aquatic life and are unable to move on land, except for the genus Laticauda, which has limited land movement. They are found in warm coastal waters from the Indian Ocean to the Pacific and are closely related to venomous terrestrial snakes in Australia.