Snakes of the sea

Sea snakes occupy a huge amount of the worlds' oceans filling various niches from the pelagic going Yellow bellied sea snake (Pelamis platura) to the Australian beaked sea snake (Enhydrina zweifeli) that regularly ventures into freshwater rivers (Cogger, 2014). However, all ‘true’ sea snakes are in the subfamily Hydrophiinae and share the same reproductive strategy of viviparity. The Sea kraits (Laticaudae subfamily, not to be confused with true sea snakes or land kraits of the Bungarus genus) show superficial similarities to true sea snakes with their largely marine habit, flattened paddle-like tail and highly toxic venom. Their habit of terrestrial exploitation for mating, laying eggs and digestion led to their own subfamily classification. In fact sea snakes are more closely related to the terrestrial elapids than the sea kraits (Cogger, 2014).

Laticauda colubrina

Pelamis platura

Sea snake and sea kraits are a prime example of convergent evolution both developing the analogous characteristic of the paddle shaped tail to aid in movement through water (McDowell, 1969). The tail of sea kraits is a simple paddle supported by unmodified vertebrae unlike the highly modified vertebrae of the true sea snakes (Fig.1). Even within the true sea snakes the paddle tail has evolved separately many times (Sanders et al, 2012).

Fig.1 Sections of modified vertebrae to aid in support of paddle tail of six sea snake species (Sanders et al, 2012).

Both families belong to the family Elapidae and are proteroglyphs (Cogger, 2014). Venom from both Hydrophiinae and Laticaudae species are often potently neurotoxic and have caused many fatalities globally (Tamiya et al, 1983; Heatwole, 1969). Most deaths occur in S.E Asia where a high diversity of both subfamilies is found, a strong reliance on net fishing practices and poor medical facilities all contribute to a heightened incidence of fatalities (Heatwole, 1969). Most species of both Sea snakes and Sea krait are notoriously docile however the curious nature of some species is often mistaken for aggression and causes an inflammatory reaction from divers (Cogger 2014).



References
Cogger, H., (2014). “Reptiles and amphibians of Australia.” 7th ed. CSIRO Publishing.

Heatwole, H., (1999). “Sea snakes.” (No. ed. 2). Krieger Publishing Company.

McDowell, S.B., (1969). “Notes on the Australian sea-snake Ephalophis greyi M. Smith (Serpentes: Elapidae, Hydrophiinae) and the origin and classification of sea-snakes.” Zoological Journal of the Linnean Society, Vol: 48, No: 3, pp. 333–349.

Sanders, K.L., Rasmussen, A.R. and Elmberg, J., (2012). Independent innovation in the evolution of paddle-shaped tails in viviparous sea snakes (Elapidae: Hydrophiinae). Integrative and comparative biology, First published online May 24, 2012 doi:10.1093/icb/ics066.

Tamiya, N., Sato, A., Kim, H.S., Teruuchi, T., Takasaki, C., Ishikawa, Y., Guinea, M.L., McCoy, M., Heatwole, H. and Cogger, H.G., (1983). “Neurotoxins of sea snakes genus Laticauda.” Toxicon, Vol:21, No:3 pp.445-447.

Images
Pelamis platura: Cogger, H. (2014). “Reptiles and amphibians of Australia.” 7th ed. CSIRO Publishing.
Laticauda colubrina :https://www.robertharding.com/preview/860-282736/banded-sea-krait-surface-amatildecopydatildecopye-islet-new-caledonia/