Somasteroidea

The Somasteroidea, or Stomasteroidea, is an extinct order of asterozoan echinoderms first defined in 1951 by W. K. Spencer.[1] Their first appearance in the fossil record was in the Early Ordovician (Tremadocian) and they had become extinct by the Late Devonian (Famennian). They are similar to the asteroids in that their bodies are flattened dorsoventrally and they have five petaloid arms with broad bases. The ambulacral plates in somasteroids are simple and unspecialized, and the arms were thought to be not flexible and were unable to assist in feeding, but the oral mouth parts were more complex.[6] According to the World Register of Marine Species, Stelleroidea is no longer considered valid and it has since been absorbed into Somasteroidea and Asterozoa.[7]

Somasteroidea
Temporal range: Tremadocian to Famennian
Holotype of Villebrunaster fezouataensis, a basal member of the Somasteroidea
Scientific classification
Kingdom:
Animalia
Phylum:
Echinodermata
Subphylum:
Asterozoa
Order:
†Somasteroidea

Spencer, 1951[1]
Families
  • †Archegonasteridae Spencer, 1951[1]
  • †Archophiactinidae? Spencer, 1927[2]
  • †Catervaparmasteridae Blake, 2000[3]
  • †Chinianasteridae Spencer, 1951[1]
  • †Helianthasteridae? Owen, 1965[4]
  • †Villebrunasteridae Fell, 1963[5]
Synonyms
  • Stelleroidea Gregory, 1900 (in part)

References
  1. W. K. Spencer. (1951). Early Palaeozoic starfish. Philosophical Transactions of the Royal Society of London, series B 235(B623):87-129
  2. W. K. Spencer. (1927). A monograph of the British Palaeozoic Asterozoa. Monograph of the Palaeontographical Society, London 1925(7):325-388
  3. D. B. Blake. (2000). An Archegonaster-like somasteroid (Echinodermata) from Pomeroy, co. Tyrone, Northern Ireland. Irish Journal of Earth Sciences 18:89-99
  4. H. G. Owen. (1965). A monograph of the British Palaeozoic Asterozoa. Table of contents, supplement and index. Monograph of the Palaeontographical Society, London 1964:541-583
  5. H. B. Fell. (1963). A new family and genus of Somasteroidea. Transactions of the Royal Society of New Zealand, Zoology 3(13):143-146
  6. Somasteroidea Tree of Life Web Project. Retrieved 2011-09-29.
  7. Asterozoa World Register of Marine Species. Retrieved 2011-09-29.


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