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Cyathaspidida
Cyathaspidida is a taxon of extinct cyathaspidid heterostracan agnathans whose fossils are found in Silurian to Lower Devonian marine strata of Europe and North America.〔Lundgren, Mette, and Henning Blom. "Phylogenetic relationships of the cyathaspidids (Heterostraci)." GFF 135.1 (2013): 74-84.〕 In life, they are thought to be benthic animals that lived most of their lives mostly buried in the substrate.
==Taxonomy==
The cyathaspidids of Cyathaspidida were tadpole-like animals with drum-shaped, cigar-shaped or wedge-shaped cephalothoraxes, and were anatomically similar to several other heterostracan groups. However, with some groups, such as the traquairaspids, cardiopeltids, and corvaspidids, this similarity appears to be superficial. With other groups, namely the tolypelepidids, the similarity suggests a close relationship. The type genus of the tolypelepidids, ''Tolypelepis'', in particular, was determined to be the sister-taxon of Cyathaspidida.〔 Originally, the cyathaspidid genera were organized together within the family Cyathaspididae. Later, the genera were then organized into subfamilies, and these subfamilies would eventually be promoted to full familial status, including Irregularaspididae, Anglaspididae, Poraspididae, Ctenaspididae, etc. In 2013, Lundgren and Blom reassessed several specimens of cyathaspidids, and reorganized them into three families, Cyathaspidae, Ariaspidae and Ctenaspidae.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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