Congo water cobra

The Congo water cobra (Naja christyi), also known as Christyi's water cobra is a species of venomous snake belonging to the Elapidae family and is native to sub-Saharan Africa. This species was formerly under the genus Boulengerina, but more recent research by Wallach et al has shown that Boulengerina is actually a subgenera and Boulengerina christyi is a synonym of Naja christyi. This species has no known subspecies.

Etymology
The Congo water cobra was first described by Belgian zoologist George Albert Boulenger in 1904. The generic name naja is a Latinisation of the Sanskrit word nāgá (नाग) meaning "cobra". The specific epithet christyi is in honor of "Dr. Cuthbert Christy", who led several biological expeditions to the Democratic Republic of the Congo.

Description
This is a medium to moderately large in length, somewhat compressed, moderately slender bodied, but heavily built snake with a medium length tapering tail. The head is short, with an indistinct canthus and distinct from the neck. The neck is capable of being spread into a hood. The eyes are relatively small in size with round pupils. Dorsal scales are smooth and shiny. The average length of an adult specimen is around 1.1 m, but they may grow upwards of 2.3 m Rostral once and a half as broad as deep, just visible from above; internasals as long as prefrontals, extensively in contact with the preocular; frontal small, not longer than broad, broadest behind forming very open angles in front and behind, not quite as long as its distance from the rostral, half as long as the parietals; supraocular much narrower than the frontal; posterior nasal in contact with the single preocular; two or three postoculars; temporals 2+2 or 2+3; seven upper labials, third and fourth entering the eye, fourth and fifth in contact with the lower postocular; four lower labials in contact with the anterior chin-shields; posterior chin-shields narrower and a little shorter than the anterior and separated by one scale. Scales in 19 rows on the neck, 17 on the body. Ventrals 221; anal entire; subcaudals 70. Colouration is blackish-brown above, the nape and the anterior third of the body with irregular pale brown and black cross bars, the black forming rings on the neck; upper lip pale brown, with black lines on the sutures between the shields; lower surface of head brownish white, belly and lower surface of tail blackish.

Distribution and habitat
This species has a small distribution range. It occurs in western Democratic Republic of Congo, the southern half of the Republic of Congo, very small portion of southeastern Gabon, and in the province of Cabinda in far northern Angola. The Congo water cobra is found most commonly in or near water, in lowland bushy or wooded areas along banks of lakes, rivers, and streams. It is limited to the lower Zaire River and nearby wet forested areas.

Behaviour and ecology
Not much is known about this species. However, it is believed to be active by day and night. It is a semi-aquatic snake which spends much of its time in the water. An excellent swimmer. It tends to hide amongst rocks, in holes or overhanging tree roots at the shore line. Also makes use of any man-made structures such as bridges and jetties to hide. Generally this is not an aggressive snake. If approached in water it will swim away swiftly. If threatened on land it will rear up, spread its narrow hood and hiss. It may strike if it's provoked extensively.

It is an oviparous species, but mating season and number of eggs layed is not known.

The Congo water cobra will prey upon fish and amphibians, but will prey upon small lizards and rodents if the opportunity is there.

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) LD50 of this species at 0.12 mg/kg. At least one human has been reported to have been bitten by this species. The individual had only mild symptoms (headache, local pain), but this species is capable of causing serious envenomation of humans. No specific antivenom currently produced against this species' venom.

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 (N. christyi toxin) residue 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 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 the lowest intraperitoneal LD50 of any African Naja species studied thus far and have high concentrations of potent postsynaptic neurotoxins.