''Scenella'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

invertebrate animal which is generally considered to be a mollusc; at various times it has been suggested that this genus belongs with the

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s, the

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, or the helcionellids, although no firm association with any of these classes has been established. An affinity with the

hydrozoa Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...

(as a flotation device) has been considered, although some authors oppose this hypothesis. A gastropod affinity is defended on the basis of six pairs of internal muscle scars, whilst the serially-repeated nature of these scars suggests to other authors a monoplacophoran affinity. However the specimens showing this scarring have not been convincingly shown to belong to the genus ''Scenella''. A similarity to the Ediacaran '' Ovatoscutum'' has also been drawn.

Description

The shell of ''Scenella'' is elongated along its anterior-posterior axis, and comprises concentric rings around a conical central peak. Radial and concentric corrugations exist in some species. Some specimens are preserved as organic films, others appear to have been infilled with calcite. They are usually preserved point-upwards, with their long axes consistently oriented; this probably represents their most stable position under their depositional current. Soft parts have never been reported in association with ''Scenella'', suggesting that the preserved fragments separated quickly from the associated tissue prior to burial.

Fossil occurrence

''Scenella'' lived from 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 ...

to the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

. Its remains have been found in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. Individual fossils are common throughout the

Burgess shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

, where they often occur in dense aggregations. Where they overlap, specimens deform as by draping. Specimens are sometimes cracked or torn, with margins often damaged by folding or "tattering". 1206 specimens of ''Scenella'' are known from the Greater Phyllopod bed, where they comprise 2.29% of the community.

Taxonomy

''Scenella'' is the only genus in the family Scenellidae. This family has no subfamilies and ''Scenella'' 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 Scenellidae. The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005 categorizes Scenellidae in the superfamilia Scenelloidea within the Paleozoic molluscs of uncertain systematic position.

Species

Species in the genus ''Scenella'' include:''Scenella''

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

, accessed 16 August 2009.

References

External links

*
''Scenella''
at the

Field Museum The Field Museum of Natural History (FMNH), also known as The Field Museum, is a natural history museum in Chicago, Illinois, and is one of the largest such museums in the world. The museum is popular for the size and quality of its educationa ...

's Evolving Planet {{Taxonbar, from=Q3951822 Burgess Shale fossils Scenellidae Prehistoric mollusc genera Cambrian invertebrates Ordovician invertebrates Extinct animals of Antarctica Paleozoic animals of Asia Prehistoric animals of Europe Paleozoic animals of North America Cambrian Series 2 first appearances Late Ordovician extinctions Paleozoic life of Ontario Paleozoic life of Newfoundland and Labrador Paleozoic life of Quebec Taxa named by Elkanah Billings