blastoid


blastoid

▪ fossil class
      any member of an extinct class (Blastoidea) of echinoderms, animals related to the modern starfish and sea lilies, that existed from the Middle Ordovician to the Late Permian periods (from 472 million to 251 million years ago). Blastoids were sedentary animals anchored to the seafloor by a stemlike column of circular plates. Unlike other echinoderms, blastoids were characterized by a regularity of structure; the blastoid body region consisted of 13 plates of calcium carbonate, an external framework, or skeleton, arranged in 3 circles about the body.

      Some blastoids are useful as index, or guide, fossils that allow the correlation of rock units; the genus Pentremites is especially well known and common.

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Universalium. 2010.

Look at other dictionaries:

  • Blastoid — Blas toid, n. (Zo[ o]l.) One of the Blastoidea. [1913 Webster] || …   The Collaborative International Dictionary of English

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  • blastoid — blas·toid …   English syllables

  • blastoid — I. ˈblaˌstȯid noun ( s) Etymology: New Latin Blastoidea, from blast + oidea : an echinoderm or fossil of the class Blastoidea II. adjective : of, relating to, or like the Blastoidea …   Useful english dictionary

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