| Helcionelloida Fossil range: Early Cambrian–Early Ordovician |
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| Latouchella costata | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Subphylum: | Conchifera |
| Class: | Helcionelloida |
| Orders | |
and see text |
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Helcionelloida is the name given to an extinct group of ancient molluscs (phylum Mollusca). These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans.
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Anatomy
These animals were untorted and they had a coiled, cone-shaped shell. The majority of species were small (shells being about two millimeters in length and or diameter). Modern reconstructions depict them as resembling snails. They also possessed a "snorkel"-like opening which was most likely used for breathing.
2005 taxonomy
The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005[1] categorizes members of this taxon within the Paleozoic molluscs of uncertain systematic position, but that taxonomy to not use the name Helcionelloida.
2006-2007 taxonomy
Taxonomy of helcionelloid according to the opinion of P. Yu. Parkhaev[2][3]:
Gastropoda Cuvier, 1797
Subclass Archaeobranchia Parkhaev, 2001
- Order Helcionelliformes Golikov & Starobogatov, 1975
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- Superfamily Helcionelloidea Wenz, 1938
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- Family Helcionellidae Wenz, 1938
- Family Igarkiellidae Parkhaev, 2001
- Family Coreospiridae Knight, 1947
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- Superfamily Yochelcionelloidea Runnegar & Jell, 1976
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- Family Trenellidae Parkhaev, 2001
- Family Yochelcionellidae Runnegar & Jell, 1976
- Family Stenothecidae Runnegar & Jell, 1980
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- Subfamily Stenothecinae Runnegar & Jell, 1980
- Subfamily Watsonellinae Parkhaev, 2001
- Order Pelagiellifomes MacKinnon, 1985
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- Family Pelagiellidae Knight, 1952
- Family Aldanellidae Linsley et Kier, 1984
Subclass Divasibranchia Minichev & Starobogatov, 1975
- Order Khairkhaniifomes Parkhaev, 2001
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- Family Khairkhaniidae Missarzhevsky, 1989
Subclass Dextrobranchia Minichev & Starobogatov, 1975
- Order Onychochiliformes Minichev & Starobogatov, 1975
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- Family Onychochilidae Koken, 1925
References
- ^ Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN 3-925919-72-4. ISSN 0076-2997. 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278
- ^ P. Yu. Parkhaev (2006) "Adaptive radiation of the Cambrian helcionelloid mollusks (Gastropoda, Archaeobranchia)." In: S.V. Rozhnov (ed.) "Evolution of the biosphere and biodiversity. Towards the 70th anniversary of A. Y. Rozanov". 2006. Moscow, pp. 282-296.
- ^ P. Yu. Parkhaev (2007). "The Cambrian ‘basement’ of gastropod evolution". Geological Society, London, Special Publications 286: 415–421. http://books.google.com/books?id=GA7-8JIh9IwC&pg=PA415.
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