Temporal range: Early Cambrian - Recent
|Various sea stars and sea urchins among mussel shells in the rocky intertidal zone of Kachemak Bay.|
Ambulacraria or Coelomopora is a Superphylum of invertebrate phyla which includes echinoderms and hemichordates; a member of this group is called an ambulacrarian. Phylogenetic analysis suggest the echinoderms and hemichordates separated around 533 million years ago. The Ambulacraria are part of the deuterostomes, a larger clade that also includes the Chordata, Vetulicolia and Saccorhytus.
The two living clades with representative organisms are:
- Echinodermata (sea stars, sea urchins, brittle stars, sea cucumbers, feather stars, sea lilies, etc.)
- Hemichordata (acorn worms, Pterobranchia, and possibly graptolites)
Fossil taxa that may lie on the stem lineage:
- Superphylum Ambulacraria
- unranked clade Cambroernida
As for many animals, the egg cell of any extant ambulacrarian by cell division evolves to a blastula ("cell ball"), which evolves to a triploblast ("three-layered") gastrula. The gastrula then evolves to a dipleurula larva form, which is specific for the ambulacraria. This, in its turn, is developed in various different kinds of larvae for different taxa of ambulacrarians.
It has been suggested that the adult form of the last common ancestor of the ambulacrarians was anatomically similar to the dipleurula larvae, whence this hypothetic ancestor sometimes also is called dipleurula.
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- Sea Cucumber Genome Imparts Insight on Genes Linked to Organ Regeneration
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