Bailey, Reeve M. Division of Fishes, Museum of Zoology, University of Michigan, Ann Arbor, Michigan.
Last reviewed:October 2019
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A collective term, also referred to as Anamniota, for the vertebrate animals that lack an amnion in development, including the Agnatha, Chondrichthyes, Osteichthyes, and Amphibia. The amnion is a protective embryonic envelope that encloses the embryo and its surrounding liquid, the amniotic fluid, during fetal life. An amnion is present in mammals, birds, and reptiles, but is absent in fishes and amphibians. In early classifications, the vertebrates were commonly separated on this basis, and the expressions Amniota and Anamnia (Anamniota) are still useful in grouping higher and lower vertebrates. It should be recognized that these terms represent grades of development, however, and do not carry the connotation of established classificatory ranks. Anamnia, then, is a group name that includes the Holocene (Recent) members of the Agnatha (jawless fishes), Chondrichthyes, Osteichthyes, and Amphibia; by presumption, the class Placodermi, which is known only from fossils, should be included in the Anamnia as well. See also: Amnion; Amniota; Amphibia; Chondrichthyes; Jawless vertebrates; Osteichthyes; Placodermi; Vertebrata
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