Hydrophis schistosus (Daudin, 1803)
Enhydrina schistosa, commonly known as the beaked sea snake, (Sinhala: වාලක්කඩියා), hook-nosed sea snake, common sea snake, or the Valakadiyan sea snake, is a highly venomous species of sea snake common throughout the tropical Indo-Pacific. This species is implicated in more than 50% of all bites caused by sea snakes, as well as the majority of envenomings and fatalities.
The rostral scale is longer than broad, and is in contact with four shields; frontal more long than broad, shorter than the parietals; nasals in contact with the two anterior labials; sometimes partially divided; one pre- and one or two postoculars; temporals l–3; seven or eight upper labials, fourth or third and fourth entering the eye, the last sometimes divided; anterior chin-shields rather indistinct, separated. Scales with a tubercle or keel, in 50–70 rows; ventrals 230–314, slightly enlarged. The snake is usually uniformly dark grey above; sides and lower parts whitish. Young specimens olive or grey with black transverse bands, broadest in the middle. Length of head and body 1110 mm; tail 190 mm.In Kerala state of India it is called the Valakadiyan.
It is found in the Arabian Sea and Persian Gulf (off Oman), south of the Seychelles and Madagascar, the seas off South Asia (Pakistan, India and Bangladesh), Southeast Asia (Myanmar, Thailand, Vietnam).
Snakes from Australia (Northern Territory and Queensland) and New Guinea are now provisionally identified as Enhydrina zweifeli, due to DNA tests that have shown they are not related to Enhydrina schistosa.
Habitat and behavior
These snakes are generally found in the coast and coastal islands of India. They are amongst the most common of the 20 kinds of sea snakes found in that region.
They are active both during the day and at night. They are able to dive up to 100 m and stay underwater for a maximum of five hours before resurfacing. Sea snakes are equipped with glands to eliminate excess salt. They are venomous and notably aggressive, with some herpetologists describing them as "cantankerous and savage". About 1.5 milligrams of its venom is estimated to be lethal
Their principal food is fish.
The venom of this species is made up of highly potent neurotoxins and myotoxins. This widespread species is responsible for the vast majority of deaths from sea snake bites (up to 90% of all sea snake bites). The LD50 value is 0.1125 mg/kg based on toxicology studies. The average venom yield per bite is approximately 7.9–9.0 mg, while the lethal human dose is estimated to be 1.5 mg.
- Valenta 2010, p. 153
- Rooij, Nelly de 1917 Reptiles of the Indo-Australian archipelago. E J Brill
- Ukuwela, K.D.B. et al. (online 2012): Molecular evidence that the deadliest sea snake Enhydrina schistosa (Elapidae: Hydrophiinae) consists of two convergent species. Molecular Phylogenetics and Evolution, doi:10.1016/j.ympev.2012.09.031
- fox News, Deadliest sea snake splits in two, By Douglas Main,, December 11, 2012
- Heatwole, Harold (1987). Sea Snakes. NSW, Australia: UNSW Press. p. 121. ISBN 9780868407760. Retrieved 30 July 2020.
- O'Shea, Mark (2005). Venomous Snakes of the World. New Jersey, USA: Princeton U Press. ISBN 978-0-691-15023-9.
- Beaked Sea Snake
- LD50 of Beaked Sea Snake Archived February 1, 2012, at the Wayback Machine
- LD50 Menu Archived April 13, 2012, at the Wayback Machine
- Heatwole, H. (1999). Sea Snakes. New South Wales: University of New South Wales Press.
- Voris, Harold K. (1985). "Population size estimates for a marine snake (Enhydrina schistosa) in Malaysia." Copeia 1985 (4): 955–961
- Valenta, Jiri (2010). Venomous Snakes: Envenoming, Therapy (2nd ed.). Hauppauge, NY: Nova Science Publishers. ISBN 978-1-60876-618-5.
- Whitaker, Romulus Earl (1978). Common Indian Snakes: A Field Guide. Delhi: Macmillan. OCLC 4638773. CS1 maint: discouraged parameter (link)