Banded Water Cobra

''Naja annulata'' (formerly ''Boulengerina annulata''), commonly known as the banded water cobra or the ringed water cobra, is a species of water cobra native to western and central Africa.

The species is one of the two species of water cobra in the world, the other one being the Congo water cobra (''Naja christyi'').

Description

It is a large, heavy-bodied snake with a short, broad and flat head with an indistinct canthus and distinct from the neck. It has medium-sized dark eyes with round pupils. The body is cylindrical; the tail is long. The scales are smooth and glossy, in 21–23 rows at midbody. Adults grow to an average of in length, but they can grow to a maximum of . Scales are smooth, indicating the largely aquatic life of this species. It is capable of spreading a narrow, yet impressive hood. Body colors are mostly glossy brown, grayish-brown, or reddish-brown with black bands all along the body. The belly is pale yellow, while the tail is wholly black.

Distribution and habitat

This species is found in parts of central and western Africa, in Burundi, Cameroon, Central African Republic, Democratic Republic of Congo, Republic of Congo, Equatorial Guinea, Gabon, Rwanda, and the province of Cabinda in Angola, as well as along the Burundian, Tanzanian and Zambian shores of Lake Tanganyika. It is largely an aquatic species and rarely is found far away from water. It can be found along lakes and rivers in forested and well-wooded savanna terrain where cover is sufficient, most commonly along lowland forested, bushy or wooded banks of lakes, rivers, and streams.

Behavior and diet

It is a secretive species and is seldom encountered by humans. It is active by day and night, though it is usually more active by day. This largely aquatic snake spends most of its time in the water. It is an excellent swimmer and is capable of remaining underwater for up to 10 minutes and diving to depths of . It is a slow mover on land, and it tends to hide among rocks, in holes, or overhanging tree roots at the shoreline. It also makes use of any man-made structures, such as bridges and jetties, to hide. It is generally not aggressive, and if approached in water, it will swim away swiftly and on land will attempt to escape into water. If threatened on land, it will rear up and spread its narrow, yet prominent hood and it may hiss loudly, but it tends not to make any forward movements. It will only bite when provoked.

It preys almost exclusively on fish. It may also prey on frogs, toads, and other amphibians.

Venom

The venom of this species is not well studied, but it is believed that the venom is dangerously neurotoxic, like that of most elapids. A study listed the intraperitoneal (IP) of this species at 0.143 mg/kg.

Venoms of the water cobras were assayed for lethality, proteolytic activity and protein content. ''Naja annulata annulata'' and ''Naja christyi'' venoms averaged 89% protein and lacked proteolytic activity. The murine intraperitoneal LD₅₀ of ''N. a. annulata'' and ''N. christyi'' venoms were 0.143 and 0.120 mg/kg, respectively. Polyvalent antivenom produced by the South African Institute of Medical Research neutralized 575 and 200 LD₅₀ of ''N. a. annulata'' and ''N. christyi'' venoms/ml antivenom, respectively. Cation exchange chromatography resolved four lethal peaks from ''N. a. annulata'' venom and six lethal peaks from ''N. christyi'' venom. The major lethal peaks (about 12% of total venom protein) were purified further with molecular sieve chromatography and were characterized as 61- (''N. a. annulata'' toxin) and 62-residue (''N. christyi'' toxin) polypeptides with four half-cystines. Elucidation of the complete amino-acid sequences indicated that these toxins belonged to the short-chain class of postsynaptic neurotoxins. Short-chain neurotoxins 1 from ''N. a. annulata'' and ''N. christyi'' had murine intraperitoneal LD₅₀ values of 0.052 and 0.083 mg/kg, respectively, and showed over 80% homology with ''N. nigricollis'' alpha toxin. Reverse-phase analysis of another peak present in both venoms resolved a toxin that had an N-terminus identical to ''N. christyi'' short-chain neurotoxin 1. These fractions also contained toxins readily separable from the short-chain isotoxin by preparative reverse-phase chromatography. Amino-acid sequencing of the first 28 residues indicated that both toxins were long-chain neurotoxins with identical N-termini. The LD₅₀ of long-chain neurotoxins 2 from ''N. a. annulata'' and ''N. christyi'' venoms were 0.086 and 0.090 mg/kg, respectively. The venoms of these little-known elapids have some of the lowest intraperitoneal LD₅₀ values of any African ''Naja'' species studied thus far, and have high concentrations of potent postsynaptic neurotoxins.

Taxonomy

References

* Mark O'Shea, Tim Halliday, ''Reptiles and amphibians'' ()

{{Taxonbar, from=Q2703922

annulata
Snakes of Africa
Reptiles of Angola
Vertebrates of Burundi
Reptiles of Cameroon
Reptiles of the Central African Republic
Reptiles of the Democratic Republic of the Congo
Reptiles of Gabon
Reptiles of Tanzania
Reptiles of Zambia
Reptiles described in 1876
Taxa named by Wilhelm Peters