Eocrinoidea
Template:Short description Template:Paraphyletic group
The Eocrinoidea were an extinct class of echinoderms that lived between the Early Cambrian and Late Silurian periods. They are the earliest known group of stalked, brachiole-bearing echinoderms, and were the most common echinoderms during the Cambrian.
The earliest genera had a short holdfast and irregularly structured plates. Later forms had a fully developed stalk with regular rows of plates. They were benthic suspension feeders, with five ambulacra on the upper surface, surrounding the mouth and extending into a number of narrow arms.[1][2]
Phylogeny
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Early evolution
The following cladogram, after Nardin et al. 2017,[4] shows the progression of early eocrinoid families, with all other eocrinoid families (including representatives Trachelocrinus and Ridersia) grouped with "derived Blastozoans" as their relationships with each other and with other blastozoans are not addressed.
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Note that some other sources use a more restricted definition of Eocrinidae,[5] or use the spelling Lichenoididae in place of Lichenoidae.[6]
Relationships to other groups
Relationships among the eocrinidae and other blastozoan clades are an area of ongoing study. Below are two of many cladograms showing some aspect of eocrinoid paraphyly or polyphyly.
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Stalked Cambrian (and select Ordovician) echinoderms, after Zamora & Smith, 2011.[7] All genera except those bracketed as "Crinoids" are blastozoans.
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References
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- ↑ Script error: No such module "Footnotes". (Note: The text groups Sanducystis with eocrinoids as the outgroup, but the paper cited classifies it as a glyptocystitoid; it is shown un-bracketed on this page. Similarly, the text classifies Macurdablastus as a eublastoid, but the cited paper has it as the sister of Eublastoidea; it is shown outside of Eublastoidea on this page.)Script error: No such module "Check for unknown parameters".
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Works cited
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