Agkistrodon is a genus of pit vipers commonly known as American moccasins. The genus is endemic to North America, ranging from the northeastern United States to northern Costa Rica. all of them monotypic and closely related. Common names include: cottonmouths, copperheads, and cantils.
Name origin
The name Agkistrodon comes from the Greek words (, 'fishhook', with the irregular transliteration gk rather than the usual nk) and () 'tooth' and is likely a reference to the fangs. Another source for this name may be the Native American word "mokesoji" of unknown origin and meaning.
Description
thumb|left|[[Agkistrodon bilineatus showing the large symmetrical platelike scales on the crown of the head that are characteristic of all species in the genus. The hazy blue eyes are typical of snakes that will soon shed their skin.]]
Members of the genus Agkistrodon have a number of features in common. All species have a relatively broad head with short fangs. A loreal scale is present, except in A. piscivorus. Usually, nine large symmetrical platelike scales are on the crown of the head, but in all species, these are often irregularly fragmented or have sutures, especially in A. bilineatus. All have a sharply defined canthus rostralis and a vertically elliptical pupil. Usually eight (6–10) supralabial scales and usually 10–11 (8–13) sublabials are present. The dorsal scales are mostly keeled and at midbody number 21–25 (usually 23), while A. piscivorus has 23–27 (usually 25). The snake has 127–157 ventral scales and 36–71 subcaudals. Of the latter, some may be divided. The anal scale is single. All have a color pattern of 10–20 dark crossbands on a lighter ground color, although sometimes the crossbands are staggered as half bands on either side of the body. support the idea that A. bilineatus and A. contortrix are more closely related. However, an analysis of mitochondrial DNA, as well as more recent molecular studies, have concluded that A. bilineatus and A. piscivorus are sister taxa, with A. contortrix being a sister species to them both.
The venom of all species is assumed to be not unlike that of A. contortrix, which contains thrombin-like enzymes that act upon the coagulant activity of the blood. A study of electrophoretic patterns of proteins in venoms among and within populations of A. contortrix and A. piscivorus showed that substantial variation exists, The study found, however, that this toxic effect is simply a tool the snake can choose to employ from an accessory venom gland it has. In most instances, the viper injects a venom that tends to immobilize, not kill, its prey before ingestion. In this case, the main venom glands secrete a toxin that inhibits the prey's sympathetic response to flee or fend off its predator. This essentially stuns the animal so that the predator can easily attack.
!bgcolor="#f0f0f0"|Common name
!bgcolor="#f0f0f0"|Geographic range
|-
|200px
|A. bilineatus
(Günther, 1863)
|cantil
|eastern copperhead
|broad-banded copperhead
|Gloyd's moccasin
|northern cottonmouth
|Florida cottonmouth
|Yucatecan cantil
|Taylor's cantil