Perischoechinoidea is a subclass of primitive sea urchins that were abundant in the Palaeozoic seas. However, the great majority of species died out during the Mesozoic, as the more advanced euechinoid sea urchins became common. Today, only a single order, the Cidaroida, survives.

Perischoechinoidea
Temporal range: Middle Ordovician–Recent
Cidaris cidaris
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Echinodermata
Class: Echinoidea
Subclass: Perischoechinoidea
McCoy, 1849
Orders

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Most fossil forms had multiple columns of ambulacral plates, rather than the two rows found in all living species of sea urchin. They also lacked a perignathic girdle around the mouth.

Taxonomy

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The group is probably a paraphyletic assemblage of stem forms, united only by their lack of more advanced features, rather than a true taxonomic clade.

Subclass Perischoechinoidea

References

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  • Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 980. ISBN 0-03-056747-5.
  • National History Museum. "Palaeozoic Echinoidea". Retrieved 20 Dec 2009.