Scenella is an extinct genus of fossil invertebrate animal which is generally considered to be a mollusc; at various times it has been suggested that this genus belongs with the gastropods, the monoplacophorans, or the helcionellids, although no firm association with any of these classes has been established.[4] An affinity with the hydrozoa (as a flotation device) has been considered,[1] although some authors oppose this hypothesis.[5] A gastropod affinity is defended on the basis of six pairs of internal muscle scars,[6] whilst the serially-repeated nature of these scars suggests to other authors a monoplacophoran affinity.[1] However the specimens showing this scarring have not been convincingly shown to belong to the genus Scenella.[1] A similarity to the Ediacaran Ovatoscutum has also been drawn.[7]
| Scenella Temporal range: | |
|---|---|
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| Dorsal view of the shell of Scenella tenuistriata | |
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| lateral view of the shell of Scenella tenuistriata | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Superfamily: | |
| Family: | † Scenellidae S. A. Miller, 1889[2] |
| Genus: | Scenella Billings, 1872 |
| Synonyms[3] | |
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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.[7] Some specimens are preserved as organic films, others appear to have been infilled with calcite.[1] They are usually preserved point-upwards, with their long axes consistently oriented; this probably represents their most stable position under their depositional current.[1] Soft parts have never been reported in association with Scenella, suggesting that the preserved fragments separated quickly from the associated tissue prior to burial.[1]
Fossil occurrence
Scenella lived from the Cambrian to the Ordovician. Its remains have been found in Antarctica, Asia, Europe, and North America. Individual fossils are common throughout the Burgess shale, where they often occur in dense aggregations.[1] Where they overlap, specimens deform as by draping.[1] Specimens are sometimes cracked or torn, with margins often damaged by folding or "tattering".[1] 1206 specimens of Scenella are known from the Greater Phyllopod bed, where they comprise 2.29% of the community.[8]
Taxonomy
Scenella is the only genus in the family Scenellidae. This family has no subfamilies and Scenella is the type genus of the family Scenellidae.
The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005[3] categorizes Scenellidae in the superfamilia Scenelloidea within the Paleozoic molluscs of uncertain systematic position.
Species
Species in the genus Scenella include:[9]
| Species | Authority | Range |
|---|---|---|
| Scenella affinis | Ulrich and Schfield, 1897 | |
| Scenella amii | (Matthew, 1902) Babcock and Robinson 1988 | Burgess Shale (Mid Cambrian, 508 million years ago)[8] |
| Scenella anomala | (Billings, 1865) Wagner 2008 | |
| Scenella augusta | (Billings, 1865) Wagner 2008 | |
| Scenella barrandei | (Linnarsson, 1879) (Bergerg-Madsen and Peel, 1986)[10] | |
| Scenella beloitensis | Ulrich and Scofield (1897) | |
| Scenella clotho | Walcott, 1936 | |
| Scenella compressa | Ulrich and Scofield (1897) | |
| Scenella conica | Whiteaves, 1884 | |
| Scenella conula | (Walcott, 1884) | |
| Scenella conicum | (Whitfield, 1886) Ulrich and Scofield (1897) | |
| Scenella hujingtanensis | Yu, 1979 | |
| Scenella magnifica | Ulrich and Scofield (1897) | |
| S.? mira | Vasil’yeva, 1994 | |
| Scenella montrealensis | Billings (1865) | |
| Scenella obtusa | (Sardeson, 1892) Ulrich and Scofield (1897) | |
| Scenella orithyia | (Billings, 1865) Ulrich and Scofield (1897) | |
| Scenella pretensa | Raymond, 1905 | |
| Scenella radialis | Ulrich and Scofield (1897) | |
| Scenella radians | Babcock & Robinson | |
| Scenella radiata | Yu, 1979 | |
| Scenella reticulata | (Billings, 1872) (type)[11] | |
| Scenella retusa | (Ford, 1873)[12] | |
| Scenella unicarinata | (Kobayashi, 1934) Wagner 2008 | |
| Scenella varians | Walcott 1908 | |
| Scenella venillia | (Billings, 1865) Wagner 2008 | |
| Scenella tenuistriata | Chapman, 1911 | Mid Cambrian[13] |
References
External links
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