Conulata

From Palaeos

o Radiata (grade)
|?--Ctenophora
`--+--Cnidaria  
   |  |--Anthozoa
   |  `--+--Hydrozoa
   |     `--+--+--Scyphozoa
   |        |  `--Cubozoa
   |        `?-Conulata (polyphyletic?)
   `--Bilateria

[edit] Conulata

Phylum: ?Cnidaria

Range: Ediacaran or Ordovician to Triassic

Description: The Conulata were a long-lived class of Palaeozoic sessile invertebrates of uncertain relationships. They possessed a pyramidal, usually four-sided, flexible test composed of calcium phosphate rods connected by a thin integument. Features of the soft anatomy of the class are largely unknown. Earlier conulariids showed less mineralisation of the test than later forms, and taxa from before the Ordovician are not universally accepted as Conulata.

Relationships: The Conulata have been connected to a number of taxa in the past, such as Mollusca, Hemichordata and Conodonta. The most popular hypothesis has related them to the Cnidaria, specifically the Scyphozoa, due to comparisons between the four-fold symmetry of most conulariids and modern scyphozoans. Homology has even been suggested between the conulariid test and the theca of modern Coronata, an order of sessile scyphozoans, based on microstructure and growth pathologies. Mitigating against a scyphozoan connection for conulariids is the absence of a phosphate skeleton in other cnidarians (though some cnidarians do possess small-scale phosphate biomineralisation), the uniqueness of the conulariid skeletal architecture, and the fact that four-fold symmetry is less obviously a feature of early taxa assigned to Conulata such as the Hexanguloconariida (which have six-fold symmetry).

Ivantsov and Fedonkin (2002) described Vendoconularia triradiata from the Ediacaran of Russia with a similar architecture to later Conulata, albeit non-mineralised, and triradial symmetry. On the basis of the latter feature they tentatively suggested a connection between Conulata and the Ediacaran to early Cambrian class Trilobozoa, a group of probably coelenterate-grade animals of equally uncertain origins.

[edit] References

Ivantsov, A. Yu., & M. A. Fedonkin. 2002. Conulariid-like fossil from the Vendian of Russia: A metazoan clade across the Proterozoic/Palaeozoic boundary. Palaeontology 45 (6): 1219-1229.

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