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. An affinity with the hydrozoa (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 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. 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 type genus 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, accessed 16 August 2009.
Species Authority Range Scenella affinis Ulrich and Schfield, 1897 Scenella amii (Matthew, 1902) Babcock and Robinson 1988 Burgess Shale (Mid Cambrian, ) Scenella anomala (Billings, 1865) Wagner 2008 Scenella augusta (Billings, 1865) Wagner 2008 Scenella barrandei (Linnarsson, 1879) (Bergerg-Madsen and Peel, 1986) 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) Scenella retusa (Ford, 1873) Scenella unicarinata (Kobayashi, 1934) Wagner 2008 Scenella varians Walcott 1908 Scenella venillia (Billings, 1865) Wagner 2008 Scenella tenuistriata Chapman, 1911 Mid CambrianChapman F. (1911). "New or Little Known Victorian Fossils in the National Museum". Proceedings of the Royal Society of Victoria, Melbourne 23: 305-324. plate 58-61.; Scenella tenuistriata at 313-314, plate LIX. figure 18 a,b.
References
External links
Scenella at the Field Museum's Evolving Planet