''Yochelcionella'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of basal

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s which lived during the Tommotian

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

, the first epoch of the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

period. This genus is often reconstructed to resemble

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

s. ''Yochelcionella'' is the

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

of the family Yochelcionellidae.

Description

Water current Yochelcionella cyrano svg hariadhi

This genus of molluscs possessed shells which were shaped like curved caps, with an

exhaust pipe An exhaust system is used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall syste ...

shaped " snorkel" emanating underneath where the apex (point of the shell) curves over. It is believed that the "snorkel" was used in breathing, allowing waste water to flow away from the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

Taxonomy

When they were first discovered, they were originally thought to be

monoplacophora Shell of Monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic class of molluscs with a cap-like shell, inhabiting deep sea environments. Extant representatives were not recognized as such until 1952; previously they wer ...

ns. Their snorkel may represent a move towards a tubular shell, such as is seen in the modern

scaphopod Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class (biology), class of shelled Marine life, marine inve ...

s. It has also been interpreted as a precursor to the cephalopod funnel or siphuncle. The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005Bouchet 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. . . 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278 categorizes ''Yochelcionella'' in the family Yochelcionellidae within the superfamilia Yochelcionelloidea within the Paleozoic molluscs of uncertain position within Mollusca (Gastropoda or Monoplacophora). For an alternate 2007-2007 taxonomy by P. Yu. Parkhae see

Helcionelloida Helcionelloida is 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. The class was ere ...

Species

Species in the genus ''Yochelcionella'' include: * '' Yochelcionella americana'' Runnegar & Pojeta, 1980 * '' Yochelcionella angustiplicata'' * '' Yochelcionella chinensis'' Pei, 1985 * '' Yochelcionella crassa'' Zhegallo in Esakova et Zhegallo, 1996 * '' Yochelcionella cyrano'' Runnegar and Pojeta 1974

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

. Its type locality is ANU Collection 10352, 16 km northeast of Mootwingee Aboriginal Site, which is in a Solvan carbonate limestone in the Coonigan Formation of Australia.. * '' Yochelcionella daleki'' * '' Yochelcionella erecta'' (Walcott, 1891)Atkins C. J. & Peel J. S. (2008). "''Yochelcionella'' (Mollusca, Helcionelloida) from the lower Cambrian of North America". '' Bulletin of Geosciences'' 83(1): 23-38 (8 figures). . * '' Yochelcionella gracilis'' Atkins & Peel, 2004 * '' Yochelcionella greenlandica'' Atkins & Peel, 2004 * '' Yochelcionella ostentata'' * '' Yochelcionella saginata'' Vendrasco et al., 2010 * '' Yochelcionella snorkorum'' Vendrasco et al., 2010Vendrasco M. J., Porter S. M., Kouchinsky A., Li G. & Fernandez C. Z. (2010). "New data on molluscs and their shell microstructures from the Middle Cambrian Gowers Formation, Australia". ''

Palaeontology Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geo ...

'' 53(1): 97-135. .

References

External links

Yochelcionellidae Palaeos

{{Taxonbar, from=Q16993581 Yochelcionellidae Cambrian molluscs Cambrian molluscs of North America Fossil taxa described in 1974 Paleozoic life of Newfoundland and Labrador Paleozoic life of the Northwest Territories Paleozoic life of Quebec Cambrian genus extinctions