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Amplexus (Latin "embrace") is a form of pseudocopulation found chiefly in amphibians and horseshoe crabs in which a male grasps a female with his front legs as part of the mating process. At the same time or with some time delay, he fertilizes the female eggs with fluid containing sperm. Fossil evidence also suggests that a certain Cambrian form of euthycarcinoid (an extinct arthropod) may also have mated by amplexus.
Amplexus chiefly occurs aquatically, but some more terrestrial anurans like the disc-tongued frogs (Discoglossidae) perform amplexus on land. In more advanced anurans like the true frogs (Ranidae), the tree frogs (Hylidae), and the true toads (Bufonidae), the amplexus is axillary (in the armpits), while in less derived anurans (the Archaeobatrachia) and frogs in the family Myobatrachidae, it is lumbar (abdominal, in front of the hindlegs). The Sooglossidae show inguinal amplexus where the male holds the female at the waist just anterior to her hind legs. Some species show cephalic amplexus where the head of the female is held while others show complete lack of amplexus.
In most anurans, the males deposit sperm onto the eggs as they are being laid, however males of the genus Ascaphus possess an intromittent organ, unique among anurans, for internal fertilization. Internal fertilization does occur in a few other genera, including Nectophrynoides, Mertensophryne, and Eleutherodactylus.
In the case of newts the process of amplexus is often observed soon after the newts become seasonally active. In the western USA, for example, this time is typically soon after the onset of the winter rainy season, when intermittent streams and vernal pools become available as breeding habitat. The rough-skinned newt is a specific widespread example of a newt in the western USA that can be observed in quiet stream pools and shallow ponds engaging in amplexus.
Amplexus occurs in all four species of horseshoe crab. The first pair of walking legs is used to tightly clasp the female in all species, and the second pair is also employed in all but Limulus polyphemus.
- Collette, Joseph H.; Gass, Kenneth C.; Hagadorn, James W. (May 2012). "Protichnites eremita Unshelled? Experimental Model-Based Neoichnology and New Evidence for A Euthycarcinoid Affinity for This Ichnospecies". Journal of Paleontology 86 (3): 442–454. doi:10.1666/11-056.1.
- Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill Publishing Company.
- Linzey, D. 2001. Vertebrate Biology, McGraw Hill Publishers, New York.
- C. Michael Hogan (2008) Rough-skinned Newt (Taricha granulosa), Globaltwitcher, ed. N. Stromberg
- Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (February 1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science 13 (1): 151–159. doi:10.2108/zsj.13.151.
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