软舌螺动物门

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软舌螺动物门
化石时期:早寒武世幸运阶 至 晚二叠纪, 536–298.9 Ma[1][2][3]
Hyoliths01.JPG
Hyolithes cerops, 爱达荷州,Spence Shale(中寒武世
科学分类 编辑
界: 动物界 Animalia
亚界: 真后生动物亚界 Eumetazoa
演化支: 两侧对称动物 Bilateria
演化支: 肾管动物 Nephrozoa
(未分级): 原口动物 Protostomia
(未分级): 螺旋動物 Spiralia
总门: 冠輪動物總門 Lophotrochozoa
门: 软舌螺动物门 Hyolitha
Marek, 1963

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

近期以軟組織化石分析發現軟舌螺動物具有觸手冠 (Lophophore) 這種進食器官,指出軟舌螺動物其實應該獨立為一門,而且和包含腕足動物門在內的觸手冠動物 (Lophophorata) 較相近[4]

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]。 有口盖英语operculum保護,還有兩條又名海倫體的彎彎附肢helens)去支撐身體,以邊緣增生英语marginal accretion的形式成長[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]

本物種的附肢叫作「海倫體」, 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]

口蓋英语operculum緊緊的把殼關閉。 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):

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]

生态[编辑]

软舌螺可能是底栖生物。 寒武纪软舌螺是全球分布,没有迹象显示有地区差异,有迹象显示软舌螺有长寿命浮游幼虫生活期;但在奥陶系不同的组合变得越来越普遍。[6]

出现[编辑]

最早的软舌螺壳体化石大约出现在5亿4000万年前的西伯利亚 Purella antiqua Zone 的Nemakit-Daldynian阶,其类似物发现于中国Paragloborilus subglobosus–Purella squamulosa Zone 的 梅树村阶寒武纪第一个阶)。[11]。软舌螺动物门物種無論在其數量及其多樣性都在寒武紀達至巔峰,之後逐步遞減,直到滅絕。[2][12]

参考文献[编辑]

  1. ^ Kouchinsky, A.; Bengtson, S.; Runnegar, B.; Skovsted, C.; Steiner, M.; Vendrasco, M. Chronology of early Cambrian biomineralization. Geological Magazine. March 2012, 149 (2): 221–251. doi:10.1017/S0016756811000720. 
  2. ^ 2.0 2.1 Malinky, J. M. Permian Hyolithida from Australia: The Last of the Hyoliths?. Journal of Paleontology. 2009, 83: 147–152. doi:10.1666/08-094R.1. 
  3. ^ 3.0 3.1 Runnegar, Bruce; Pojeta, John; Morris, Noel J.; Taylor, John D.; Taylor, Michael E.; McClung, Graham. Biology of the Hyolitha. Lethaia. 1975, 8 (2): 181. doi:10.1111/j.1502-3931.1975.tb01311.x. 
  4. ^ Joseph Moysiuk. Martin R. Smith, Jean-Bernard Caron. Hyoliths are Palaeozoic lophophorates. Nature. 2017. doi:10.1038/nature20804. 
  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. JSTOR 29739075. doi:10.1666/08-094R.1. 
  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. ^ 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)‎). 
  12. ^ Steiner, M.; Li, G.; Qian, Y.; Zhu, M.; Erdtmann, B. D. Neoproterozoic to Early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China). Palaeogeography, Palaeoclimatology, Palaeoecology. 2007, 254: 67. doi:10.1016/j.palaeo.2007.03.046.