软舌螺动物门

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软舌螺动物门
化石時期: Fortunian上二叠世[1][2][3]
表达式错误:未预料的<操作符。

表达式错误:未预料的<操作符。

Hyolithes cerops, Spence Shale, Idaho (Middle Cambrian)
Hyolithes cerops, Spence Shale, Idaho (Middle Cambrian)
科學分類
界: 动物界 Animalia
亞界: 后生动物亚界 Metazoa
超门: 冠輪動物總門 Lophotrochozoa
門: 软体动物门 Mollusca?[4]
綱: 软舌螺动物门 Hyolitha
Marek, 1963

見內文

软舌螺动物学名Hyolitha)是一種從古生代開始出現的神秘動物,具有小圓錐形的螺殼。這些物種目前都已全部滅絕;其化石一般只能保存锥壳、口盖附肢三个部分,外壳为钙质成分,两侧对称。根據形態學的分類,本物種是一类海生有壳的无脊椎动物,但再具體一點的分类众说纷纭:

  • 一种意见认为它是软体动物门之下的一个纲,
  • 另一种意见则认为它与软件动无本质上的联系,应属一个独立的门。
奥陶纪的软舌螺动物门内部铸件,爱沙尼亚北部

形態學[编辑]

软舌螺动物的碳酸鈣質外殼很大可能是由霰石組成[5]。有口盖保護,還有兩條彎彎的附肢helens)去支撐身體,all of which grew by marginal accretion[5]。 體長一般在一公分到四公分,橫切面呈三角形或橢圓形。部份物種有環紋或條紋。

外殼[编辑]

The orthothecid shell has an internal layer with a microstructure of transverse bundles, and an external layer comprising longitudinal bundles.[5]

附肢[编辑]

Helens are long structures that taper as they logarithmically coil gently in a ventral direction.[5]

The helens were calcareous, with an organic component, and had an organic-rich central core surrounded by concentric laminae of calcite. They grew by the addition of new material at their base, on the cavity side, leaving growth lines.[5] They were originally described by Walcott as separate fossils under the genus name Helenia, (Walcott's wife was named Helena and his daughter Helen); Bruce Runnegar adopted the name helen when they were recognized as part of the hyolith organism.[5]

口蓋[编辑]

The operculum closes perfectly over the aperture of the shell, leaving two gaps through which the helens can protrude.[5] It comprises two parts: the cardinal shield, a flat region at the top of the shell; and the conical shield, the bottom part, which is more conical.[5] The inside of the shell bears a number of protrusions, notably the dorsal cardinal processes and the radially-arranged clavicles.[5]

分类[编辑]

Hyoliths from the Middle Ordovician of northern Estonia; these are internal molds.

人们依据有无口唇将软舌螺动物门(纲)动物分成两个纲(目):

The hyoliths are divided into two orders, the Hyolithida and the Orthothecida.

Hyolitha have dorso-ventrally differentiated opercula, with the ventral surface of the shell extending forwards to form a shelf termed the ligula.[5]

The Orthothecida are somewhat more problematic, and probably contain a number of non-hyoliths simply because they are so difficult to identify with confidence, especially if their operculum is absent.[5] They have a straight (planar) opening, sometimes with a notch on the bottom side, and sealed with an operculum that has no ligula, clavicles, furrow or rooflets.[6]

Hyptiotheca is an unusual hyolithid, in that it lacks clavicles.[6]

Orthothecids fall into two groups: one, the orcothecida sensu stricto,[7] is kidney or heart shaped in cross-section due to a longitudinal groove on its ventral surface, and its opercula bear cardinal processes; the other has a rounded cross-section and often lacks cardinal processes, making them difficult to distinguish from other cornet-shaped calcareous organisms.[6] All were sessile and benthic; some may have been filter feeders.[7]

Phylogenetic position[编辑]

Haplophrentis carinatus from the Stephen Formation, Burgess Shale (Middle Cambrian), Burgess Pass, British Columbia, Canada.

Because hyoliths are extinct and do not obviously resemble any extant group, it is unclear which living group they are most closely related to. They may be molluscs; authors who suggest that they deserve their own phylum do not comment on the position of this phylum in the tree of life.[8] Their grade of organization is considered to be of the 'mollusc-annelid-sipunculid' level,[9] consistent with a Lophotrochozoan affinity, and comparison is usually drawn with the molluscs or sipunculids.[9][10] Older studies (predating the Lophotrochozoan concept) consider hyoliths to represent a stem lineage of the clade containing (Mollusca + Annelida + Arthropoda).[3]

Ecology[编辑]

They were probably benthic (bottom-dwellers).

In the Cambrian, their global distribution shows no sign of provinciality, suggesting a long-lived planktonic larval life stage; but by the Ordovician distinct assemblages were becoming evident.[6]

Occurrence[编辑]

The first hyolith fossils appeared about 540 million years ago in the Purella antiqua Zone of the Nemakit-Daldynian Stage of Siberia and in its analogue the Paragloborilus subglobosus–Purella squamulosa Zone of the 梅树村阶Meishucunian Stage,寒武纪第一个阶) of China[11][12]。 Hyolith abundance and diversity attain a maximum in the Cambrian, followed by a progressive decline up to their Permian extinction.[2][13]

参考文献[编辑]

  1. ^ 引用错误:没有为名为Kouchinsky2012的参考文献提供内容
  2. ^ 2.0 2.1 引用错误:没有为名为ref_的参考文献提供内容
  3. ^ 3.0 3.1 引用错误:没有为名为Runnegar1975的参考文献提供内容
  4. ^ Wotte, T. New Middle Cambrian mollucs from the Láncara Formation of the Cantabrian Mountains (north-western Spain). Revista Española de Paleontología. 2006, 21 (2): 145–158 (英语). 
  5. ^ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 Mus, M. Martí; Bergström, J. Skeletal Microstructure of Helens, Lateral Spines of Hyolithids. Palaeontology. 2007, 50 (5): 1231–1243. doi:10.1111/j.1475-4983.2007.00700.x. 
  6. ^ 6.0 6.1 6.2 6.3 Malinky, J.M.; Skovsted, C.B. Hyoliths and small shelly fossils from the Lower Cambrian of North−East Greenland. Acta Palaeontologica Polonica. 2004, 49 (4): 551–578. 
  7. ^ 7.0 7.1 Malinky, J. M. First Occurrence of Orthotheca Novák, 1886 (Hyolitha, Early Devonian) in North America. Journal of Paleontology. 2009, 83 (4): 588–596. doi:10.1666/08-164R.1. 
  8. ^ Malinky, John M. Permian Hyolithida from Australia: The Last of the Hyoliths?. Journal of Paleontology. 2009, 83: 147–152. doi:10.1666/08-094R.1. JSTOR 29739075. 
  9. ^ 9.0 9.1 Runnegar, B. Hyolitha: Status of the phylum. Lethaia. January 1980, 13: 21. doi:10.1111/j.1502-3931.1980.tb01025.x. 
  10. ^ Kouchinsky, A. V. Skeletal microstructures of hyoliths from the Early Cambrian of Siberia. Alcheringa: an Australasian Journal of Palaeontology. 2000, 24 (2): 65–81. doi:10.1080/03115510008619525. 
  11. ^ 引用错误:没有为名为.E9.92.B1.E9.80.B81977的参考文献提供内容
  12. ^ 钱逸 (编). 中国小壳化石分类学与生物地层学. 北京 (中国): 科学出版社. 1999. ISBN 7-03-007599-4 (中文(简体)‎). 
  13. ^ 引用错误:没有为名为Steiner2007的参考文献提供内容