''Cotyledion tylodes'' is an extinct, stalked

filter-feeder Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specia ...

known from the Chengjiang lagerstatten. The living animal reached a couple of centimetres in height, and bore a loose scleritome of ovoid sclerites. Its interpretation has been controversial, but it is currently thought to be a member of the

Entoprocta Entoprocta (), or Kamptozoa , is a phylum (biology), phylum of mostly Sessility (zoology), sessile aquatic animals, ranging from long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whos ...

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

History of identification

''C. tylodes'' was initially tentatively classified as a stem group

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

in 1996, and then a

lophophorate The Lophophorata (also called Tentaculata; not to be confused with Tentaculata Eschscholtz 1825, a class within the Ctenophora) are a Lophotrochozoan clade consisting of the Brachiozoa and the Bryozoa. They have a lophophore. Molecular phyloge ...

in 2002. Lophphorate affinities were challenged as based on taphonomic artifacts in a 2010 paper that suggested a

cnidarian Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

affinity based on cylyndrical symmetry as an ancestral body plan for that group. A more recent alternative proposal suggested a relationship with the Cambroernida, a group of early

deuterostomes Deuterostomes (from Greek: ) are bilaterian animals of the superphylum Deuterostomia (), typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia comprises three phyla: Chordata, Echinodermata, ...

. However, a later comprehensive paper on cambroernids did not include ''Cotyledion''. A comprehensive 2013 study of around 400 new specimens provided stronger support for a lophophorate affinity, specifically allied with the entoprocts. The clear presence of a U-shaped gut in the new specimens contradicts placement among the cnidarians, while the lack of bifurcation in the crown of tentacles makes affinity with the deuterostomes unlikely. A recent review of echinoderm origins again refuted the placement of ''Cotyledion'' with that group, agreeing with its identity as a stem entoproct.

References

Works cited

* * * * * * Maotianshan shales fossils Monotypic prehistoric protostome genera Cambrian genus extinctions {{Cambrian-animal-stub

History of identification

See also

References

Works cited