Home | | Modern Medical Toxicology | Classification of Snakes

Chapter: Modern Medical Toxicology: Organic Poisons (Toxins): Venomous Bites and Stings

| Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail |

Classification of Snakes

Snakes are classified on the basis of morphological charac-teristics such as arrangement of scales (lepidosis), dentition, osteology, myology, sensory organs, and the form of the hemipenes.

Classification of Snakes

Snakes are classified on the basis of morphological charac-teristics such as arrangement of scales (lepidosis), dentition, osteology, myology, sensory organs, and the form of the hemipenes, as well as on the basis of immunological analysis of venom and serum proteins, and sequence analysis of DNA that encodes mitochondrial and other enzymes.

There are about 3500 known species of snakes in the world, of which less than 350 species are venomous. Among non-venomous snakes, only the giant constrictors belonging to family Boidae are dangerous to man. Examples include rock python (Python sebae ) of Africa, reticulated python (Pythonreticulatus) of South East Asia, especially Indonesia, andanaconda (Eunectes murinus) of South America. The Indian rock python is seen all over India, and grows up to 3 metres, but not a single case of human fatality has been reported that can be definitely attributed to this snake. The regal python of Nepal grows up to 10 metres in length, and is said to be the largest snake in the world. The giant constrictors act by coiling around the victim and crushing him to death. Venomous snakes belong to 5 families:

1. Colubridae: This family includes almost 1400 species, or75% of all the snake genera and 78% of all the snake species in the world. Approximately 400 of these species of Colubridae have short immobile fangs, or enlarged solid teeth at the poste-rior end of the maxilla. About one third of the Colubrid species possess rear fangs which deliver a toxic saliva delivered by a chewing motion. Colubrid snakes are the predominant species on all continents except Australia. Examples include mountain racer, Western and Eastern hognose snakes, parrot snake, rat snake, wandering garter snake, etc.

2.Atractaspididae: This family comprises African and MiddleEastern burrowing asps or stilleto snakes (also known as burrowing or mole vipers or adders, false vipers, side-stabbing snakes), which have very long front fangs used for immobi-lising their prey by a side-swiping motion. These fangs often protrude from the corner of the partially closed mouth.

3.Elapidae: These snakes have relatively short, fixed front(proteroglyph) fangs, which however may extend up to 10 mm long). They are anchored at the anterior portion of the maxilla. Examples include the following—

a.Cobras (Naja)

b.  Kraits (Bungarus)

c.Coral snakes (Calliophis, Maticora, Micrurus)

d.  Mambas (Dendroaspis)

4.Viperidae: These snakes have highly developed longcurved, hinged, front fangs, which are channelised in the form of a hypodermic needle. There are two sub families— a. Viperinae or true vipers: Vipers and adders

b.Crotalinae or pit vipers: Rattle snakes (Crotalus,Sistrurus), and Asian pit vipers (Trimeresurus, Hypnale).

5.Hydrophidae: This family comprises sea snakes, whichhave short fixed fangs as in the case of the elapids. Approximately 330 species of snakes exist in India, of which about 70 species are venomous (40 land snakes and 30 sea snakes) . The commonest Indian venomous snakes are referred to as the “Big Four”, and comprise common krait (Bungarus caeruleus), common cobra (Naja naja), saw-scaled viper (Echis carinatus), and Russell’s viper (Vipera russelli).

Other venomous snakes which are less commonly encountered include the common green pit viper or bamboo snake (Lachesis gramineus), large-spotted viper (Lachesismonticola), horse-shoe viper (Trimeresurus strigatus), Gray’sviper (Trimeresurus purpureomaculatus), anamalai viper (Trimeresurus anamallensis), brown or common himalayan viper (Agkistrodon himalayanus), hump-nosed viper ( Agkistrodonhypnale), Millard’s viper (Agkistrodon millardi), large-scaledviper (Lachesis macrolepis), and mock viper (Psammodynastespulverulentus), all of which are pit vipers. Of the remaining, thefollowing are important: king cobra (Ophiophagus hannah), Bibron’s coral snake (Calliophis bibroni), Maclelland’s coral snake (Calliophis macclellandi), slender coral snake (Calliophistrimaculatus ), and common Indian coral snake (Hemibungarus nigrescens ). The commonest sea snake encountered in Indianseas is the hook-nosed sea snake (Enhydrina schistosa).






 

Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail


Copyright © 2018-2020 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.