There are several features of the serpentine form that have allowed sea snakes to adapt more readily to the marine environment than other reptiles. Marine adaptations include swimming, respiration, salt excretion, and marine fouling & skin shedding.
Snakes elongate bodies are preadapted for efficient swimming, and most sea snake species have developed a paddle shaped tail that further enhances their locomotory ability in water.
Sea snakes are air breathing reptiles and must come to the surface to breathe, however they can spend from 30 minutes to 2 hours diving between breaths. They have two major adaptations that allows them to do this.
Firstly they have one elongate cylindrical lung that extends for almost the entire length of their body which is very efficient for gas exchange. They are also able to carry out cutaneous respiration. This means that oxygen diffuses from sea water across the snake’s skin into tiny blood vessels and carbon dioxide diffuses out.
Sea snakes have nostril valves that prevent air entering the lung while underwater. Nostril valvesopen inwards and are held shut from behind by erectile tissue engorged with blood, like a penis
Sea snakes are able to avoid excess salt accumulation from sea water using a salt excreting gland, the posterior sublingual gland that sits under the tongue.
Marine fouling and shedding of skin
All snakes shed their skins. Sea snakes shed every two to six weeks, which is more frequently than land snakes and more often than needed for growth alone. The process involves rubbing the lips against coral or other hard substrate to loosen the skin. The snake then catches the skin against something to anchor it and crawls forward leaving the skin turned inside out behind it.
Skin shedding allows sea snakes to rid themselves of fouling marine organisms such as algae, barnacles and bryozoans. Otherwise they would be covered with fouling organsims like the hull of a boat that needs to be cleaned and this would interfere with the snakes ability to swim efficiently and may also cause disease.
Courtship, mating and reproduction
Like all snakes and lizards, male sea snakes have two penises. They are called hemipenes, but each is an autonomous independently functioning penis and only one is used during mating. Mating takes place for long periods and sea snakes must surface for air during that time. The female controls breathing and as she swims to the surface the male is pulled along attached via the hemipenis. At the surface the male needs to gulp for air or he has to wait til the next time the female comes up the the surface to breathe. Males are unable to disengage until mating is finished.
In species where courtship has been studied, eg olive and turtlehead sea snakes, one or more males follow the female very closely and occasionally prod the head and neck of females.
All sea snakes except the latidcaudids give birth to live young after gestation periods that range from four to eleven months, depending on the species. Most species reproduce every year. The timing of the reproductive cycle varies enomously between species and also differs between geographical locations for the same species.
Young are born underwater and must be independent immediately to swim to the surface to breathe. There is no parental care. In some species look quite different to the adults eg juvenile olive sea snake are strongly banded while the adults are not.
Cogger H (1996) Reptiles & Amphibians of Australia. Reed Books Australia, Melbourne.
Heatwole H (1999) Sea Snakes. Australian Natural History Series. University of New South Wales Press, Sydney.