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Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Cladus: Sauria
Infraclassis: Lepidosauromorpha
Superordo: Lepidosauria
Ordo: Squamata
Subordo: Serpentes
Infraordo: Caenophidia
Superfamilia: Viperoidea

Familia: Viperidae
Subfamilia: Crotalinae
Genus: Agkistrodon
Species (8): A. bilineatus – A. conanti – A. contortrix – A. howardgloydi – A. laticinctus – A. piscivorus – A. russeolus – A. taylori


Agkistrodon Palisot de Beauvois, 1799

Vernacular Names
Deutsch: Dreieckskopfottern
English: Moccasins
Türkçe: Mokasenler


Agkistrodon is a genus of pit vipers commonly known as American moccasins.[2][3] The genus is endemic to North America, ranging from the Southern United States to northern Costa Rica.[1] Eight species are currently recognized,[4][5] all of them monotypic and closely related.[6] Like all pit vipers, members of the genus are venomous. Common names include: cottonmouths, copperheads, and cantils.[7]

Name origin

The name Agkistrodon comes from the Greek words ankistron (ἄγκιστρον, 'fishhook', with the irregular transliteration gk rather than the usual nk) and odon (ὀδών)[8] 'tooth'[9] and is likely a reference to the fangs.[7]

Some varieties of the genus are given the common name "moccasin" or "moccasin snake" in the United States, which is the Algonquian word for "shoe". The origin of this nickname is unknown. The first known use of "moccasin" to refer to a deadly venomous snake was in a 1765 publication. The nickname is used to refer to both cottonmouths and copperheads. According to the Word Detective, this use may be related to their color and appearance or the silence with which they move.[10] Another source for this name may be the Native American word "mokesoji" of unknown origin and meaning.[11]
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 this genus 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.[7]

The phylogeny of the species has long been controversial. Studies based on morphological[6] and venom characteristics[12] support the idea that A. bilineatus and A. contortrix are more closely related. However, an analysis of mitochondrial DNA,[13] as well as more recent molecular studies,[14][15] have concluded that A. bilineatus and A. piscivorus are sister taxa, with A. contortrix being a sister species to them both.[7]

Geographic range
General distribution of four Latin American species: dark blue = A. bilineatus; red = A. howardgloydi; green = A. russeolus; light blue = A. taylori.

They are found in North America from the northeastern and central United States southward through peninsular Florida and southwestern Texas, and in Central America on the Atlantic versant from Tamaulipas and Nuevo León southward to the Yucatan Peninsula, Belize, and Guatemala. They are seen along the Pacific coastal plain and lower foothills from Sonora south through Guatemala, El Salvador, Honduras, and Nicaragua to northwestern Costa Rica.[1]


All are semiaquatic to terrestrial and are often found near sources of water. However, A. contortrix and A. bilineatus are also found in dry habitats, often far from permanent streams or ponds.[7]


The members of this genus are all ovoviviparous.[7]

Pit vipers of the genus Agkistrodon rely on a potent venom they produce for their survival. Used to immobilize prey and fend off predators, one bite can inject enough venom into a human to cause severe pain, swelling, weakness, difficulty breathing, hemorrhaging, gangrene, fever, vomiting, and in rare instances, even death.[16]

The venom of all three 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,[12] and no reason exists to believe that these differences do not correspond with variations in toxicity.[7]


In a study conducted at the College of Medicine at the University of Florida, venom from A. piscivorous was injected into the lymph fluid of a frog. The frog immediately suffocated because of the collapse of its lung sacs. The venom even resulted in lung constriction when directly applied to the surface of the frog's lungs. To test this, trace amounts of venom were dropped onto a single pulmonary sac in a frog's lung after it was anesthetized and its chest cavity dissected open. A drop of solution containing a venom concentration of 1 mg/ml was enough to cause contraction of the pulmonary artery adventitia after 5-8 sec in a frog weighing 40 g.[17] 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.[17]

Image Species and author[18] Common name Geographic range[1][6][7][19]
Agkistrodon bilineatus 2.jpg A. bilineatus

(Günther 1863) [20]

cantil [3]
Mexico and Central America, from southern Sonora, Mexico south to Guatemala, El Salvador, and Honduras.
Eastern Copperhead (Agkistrodon contortrix) - Flickr - 2ndPeter (1).jpg A. contortrixT

(Linnaeus 1766) [21]

eastern copperhead [2] The United States (East Texas, Oklahoma, and Kansas, eastward to the Atlantic coast, including Missouri, Arkansas, Louisiana, Mississippi, Alabama, Georgia, northern Florida, South Carolina, North Carolina, Tennessee, Kentucky, Virginia, West Virginia, Illinois, Indiana, Ohio, Iowa, Pennsylvania, Maryland, New Jersey, Delaware, New York, Connecticut, Massachusetts).
Agkistrodon contortrix laticinctus.jpg A. laticinctus

Gloyd & Conant, 1934 [22]

broad-banded copperhead [2] Eastern Kansas, central Oklahoma, central and Trans-Pecos Texas, and adjacent areas of northern Chihuahua and Coahuila, Mexico.
A. howardgloydi

Conant 1984 [23]

Gloyd's cantil

southern cantil

Northwestern Costa Rica, western Nicaragua, southern Honduras.
Cottonmouth (Agkistrodon piscivorus) photographed in Liberty Co., Texas. W. L. Farr.jpg A. piscivorus

(Lacépède 1798) [24]

northern cottonmouth [2] The eastern United States from extreme southeastern Virginia, south through peninsular Florida and west to Arkansas, southeastern Kansas, eastern and southern Oklahoma and eastern and central Texas. A few records exist from along the Rio Grande in Texas, but these are thought to represent isolated populations that possibly no longer exist.
Florida Water Moccasin 056.jpg A. conanti

Gloyd 1969 [25]

Florida cottonmouth [2] Southernmost Georgia through Florida.
A. russeolus

Gloyd, 1972 [26]

Yucatecan cantil [3] Yucatan, Mexico, northern Guatemala, northern Belize.
Agkistrodon bilineatus taylori mocassin mexicain 4.jpg A. taylori

Burger & Robertson, 1951 [27]

Taylor's cantil [3] Gulf Coast lowlands of northeast Mexico, primarily southern Tamaulipas, with a few records from adjacent areas of Nuevo Leon, San Luis Potosi, Veracruz, and Hidalgo.

Type species.[1]

This genus was previously much larger and also included the following genera:[1]

Calloselasma - Ground pit viper found in Southeast Asia (Malaya).
Deinagkistrodon - The Hundred-pace viper found mostly in southern China.
Gloydius - Ground pit vipers found in Asia.
Hypnale - Hump-nosed vipers found in India and Sri Lanka.


McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
Crother, B. I. (ed.). 2017. Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding. SSAR Herpetological Circular 43, 1–102 pp. (page 59)
Liner, E. A. and G. Casas-Andreu. 2008. Standard Spanish, English and scientific names of the amphibians and reptiles of Mexico. Society for the Study Amphibians and Reptiles. Herpetological Circular 38: i-iv, 1-162. (pages 95-96)
Porras, Louis W., Larry David Wilson, Gordon W. Schuett, and Randall S. Reiserer 2013. A taxonomic reevaluation and conservation assessment of the common cantil, Agkistrodon bilineatus (Squamata: Viperidae): a race against time. Amphibian & Reptile Conservation 7(1): 48–73.
Frank T. Burbrink, Timothy J. Guiher (2014). Considering gene flow when using coalescent methods to delimit lineages of North American pitvipers of the genus Agkistrodon. Zoological Journal of the Linnean Society, December 2014. doi:10.1111/zoj.12211
Gloyd HK, Conant R. 1990. Snakes of the Agkistrodon Complex: A Monographic Review. Society for the Study of Amphibians and Reptiles. 614 pp. 52 plates. LCCN 89-50342. ISBN 0-916984-20-6.
Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
A variant form of odοus (ὀδούς)); stem: odont- (ὀδόντ-).
ἄγκιστρον, ὀδών, ὀδούς. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
"Moccasin". The Word Detective. January 2014. Retrieved November 21, 2016.
Catherine C. Hopley (1882). Snakes: curiosities and wonders of serpent life. London, Griffith & Farran; New York, E.P. Dutton & co. "Besides that 'deadly moccasin' and frequent 'black snakes,' there were 'whip snakes,' 'milk snakes,' and many others which the negroes would bring home as trophies of their courageous slaughter; but by no scientific names were they known there. Except this name moccasin or mokesoji, which probably conveyed some especial meaning to the aborigines, few of the Indian vernaculars have been preserved in the United States, as we find them in other parts of America, which latter are treated of in chapters xxii. and xxiii. of this work ; but common English names prevail."
Jones JM (1976). "Variation of venom proteins in Agkistrodon snakes from North America". Copeia. 1976 (3): 558–562. doi:10.2307/1443375. JSTOR 1443375.
Knight A, Densmore III LD, Real ED (1992). "Molecular systematics of the Agkistrodon complex". pp. 49-70. In: Campbell JA, Brodie Jr ED (1992). Biology of the Pitvipers. Texas: Selva. 467 pp. 17 plates. ISBN 0-9630537-0-1
Parkinson CL (1999). "Molecular systematics and biogeographical history of pitvipers as determined by mitochondrial ribosomal DNA sequences". Copeia. 1999 (3): 576–586. doi:10.2307/1447591. JSTOR 1447591.
Parkinson CL, Moody SM, Ahlquist JE (1997). "Phylogenetic relationships of the "Agkistrodon complex" based on mitochondrial DNS data". pp. 63-78. In: Thorpe RS, Wüster W, Malhotra A (1997). Venomous Snakes: Ecology, Evolution, and Snakebite. Oxford: Clarendon Press
"Agkistrodon acutus pit vipers."; accessed April 2010. [1]
Gennaro JF, Hall HP, Casey ER, Hayes WK (September 2007). "Neurotropic effects of venoms and other factors that promote prey acquisition". Journal of Experimental Zoology Part A. 307 (9): 488–99. doi:10.1002/jez.405. PMID 17620305.
"Agkistrodon". Integrated Taxonomic Information System. Retrieved 2 November 2006.
Savage, JM. The Amphibians and Reptiles of Costa Rica. The University of Chicago Press, 2002, p. 719. ISBN 0-226-73537-0.
Günther. A. 1863. Third account of new species of snakes in the collection of the British Museum. Ann. Mag. Nat. Hist. (3) 12: 348 - 365
Linné, C. von [= Linnaeus, C.] 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. Laurentii Salvii, Stockholm, Holmiae. 1-532 pp.
Gloyd H. and Conant R. 1934. The broad-banded copperhead: a new spubspecies of Agkistrodon mokasen. Occasional Papers of the Museum of Zoology University of Michigan, No. 283, p. 2
Conant, R. 1984. A new subspecies of the pit viper Agkistrodon bilineatus (Reptilia: Viperidae) from Central America. Proc. Biol. Soc. Washington 97: 135-141
Lacepède, B. G. E. 1789. Histoire Naturelle des Quadrupèdes Ovipares et de Serpens. Vol.2. lmprimerie du Roi, Hôtel de Thou, Paris, 671 pp.
Gloyd, H. K. 1969. Two additional subspecies of North American crotalid snakes, genus Agkistrodon. Proc. Biol. Soc. Washington 82: 219-232
Gloyd, H. K. 1972. A subspecies of Agkistrodon bilineatus (Serpentes: Crotalidae) on the Yucatán Peninsula, México. Proc. Biol. Soc. Washington 84: 327-334.

Burger, W.L. & Robertson,W.B. 1951. A new subspecies of the Mexican moccasin, Agkistrodon bilineatus. Univ. Kansas Sci. Bull. 34 (5): 213-218

Further reading

Daudin FM (1801-1803). Histoire naturelle, générale et particulière des reptiles: ouvrage faisant suit à l'histoire naturelle générale et particulière, composée par Leclerc de Buffon; et rédigée par C.S. Sonnini, miembre de plusieurs sociétés savantes. 8 vols. Paris: F. Dufart. (in French). [For a discussion of the publication date, see Harper F (1940). American Midland Nataturalist 23: 693].
Fischer JG (1813). Zoognosia tabulis synopticus illustrata, in usum praelectionum Academiae Imperialis medico-chirurgicae Mosquensis edita. 3d ed. vol. 1, pt. 3 (Reptiles, Poissons): 57-117. Moscow: Nicolai Sergeidis Vsevolozsky. (in Latin).
Fitzinger LJ (1826). Neue Classification der Reptilien nach ihren natürlichen Verwandtschaften: nebst einer Verwandtschafts-Tafel und einem Verzeichnisse der Reptilien-Sammlung des K. K. Zoologischen Museums zu Wien. Vienna: J.G. Heubner. five unnumbered + 67 pp. + one plate. (in German and Latin).
Hubbs B, O'Connor B (2012). A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tempe, Arizona: Tricolor Books. 129 pp. ISBN 978-0-9754641-3-7.
Link HF (1807). Beschreibung der naturalien-sammlung der Universität zu Rostock. Zweite abtheilung, pp. 51–100. Rostock: Gebruckt bei Adlers Erben. (in German).
Palisot de Beauvois AMFJ (1799). "Memoir on Amphibia. Serpentes". Transactions of the American Philosophical Society. 4: 362–381. doi:10.2307/1005115. JSTOR 1005115.
Sonnini CS, Latreille PA (1801). Histoire naturelle des reptiles, avec figures dissinees dápres nature. 4 Vols. Paris: Deterville. (in French). [For a discussion of the publication date, see Harper F (1940). American Midland Naturalist 23: 692-723].
Troost G (1836). "On a new genus of serpents, and two new species of the genus Heterodon, inhabiting Tennessee". Ann. Lyc. Nat. Hist. New York. 3: 174–190.
Wagler JG (1830). Natürliches System der Amphibien, mit vorangehender Classification der Säugthiere und Vögel. Ein Beitrag zur vergleichenden Zoologie. Munich, Stuttgart and Tübingen: J.G. Cotta. vi + 354 pp. + one plate. (in German and Latin).


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