First Specimens of the Cornutan Stylophoran Phyllocystis (Echinodermata) in the Ordovician (Volkhov Regional Stage, Dapingian and Darriwilian) of Baltica and Special Aspects of Stylophoran Axial Symmetry

IF 0.7 4区 地球科学 Q4 PALEONTOLOGY
S. V. Rozhnov, G. A. Anekeeva
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引用次数: 0

Abstract

Two new species of cornutan stylophora of the genus Phyllocystis are described from the Volkhov Regional Stage (Middle Ordovician, Dapingian) of Baltica. This indicates a biogeographic connection between the Afro-European part of Gondwana and Baltica since the very beginning of the Middle Ordovician. Both species were confined to cold-water, shallow basins with low water mobility. Analysis of the axial symmetry of stylophorans and the location of the hydropore indicates the absence of torsion in their ontogeny and the location of the ambulacral system to the right of their anteroposterior axis. To explain this morphology, two alternative hypotheses are proposed: (1) inversion in the development of right and left coeloms; (2) inverted state of stylophorans compared to other invertebrates, in which respect they resemble chordates in terms of the position of the dorsal and ventral sides.

Abstract Image

波罗的海奥陶纪(沃尔霍夫地区阶段、达平纪和达里维利纪)粟米瓣柱孢藻(棘皮动物门)的首个标本以及柱孢藻轴对称的特殊方面
摘要描述了来自波罗的海沃尔霍夫地区阶段(中奥陶世,大平阶)的两个新的矢车菊属物种。这表明从中奥陶世一开始,冈瓦纳的非洲-欧洲部分与波罗的海之间就存在着生物地理联系。这两个物种都局限于水流动性低的冷水浅盆地。对石龙子的轴对称和水孔位置的分析表明,石龙子在本体发育过程中没有扭转,伏肛系统位于前胸轴的右侧。为了解释这种形态,提出了两种替代假说:(1) 左右腔室发育倒置;(2) 花柱虫与其他无脊椎动物相比处于倒置状态,在背侧和腹侧的位置上与脊索动物相似。
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来源期刊
Paleontological Journal
Paleontological Journal 地学-古生物学
CiteScore
1.20
自引率
33.30%
发文量
70
审稿时长
6-12 weeks
期刊介绍: Paleontological Journal (Paleontologicheskii zhurnal) is the principal Russian periodical in paleontology. The journal publishes original work on the anatomy, morphology, and taxonomy of fossil organisms, as well as their distribution, ecology, and origin. It also publishes studies on the evolution of organisms, ecosystems, and the biosphere and provides invaluable information on global biostratigraphy with an emphasis on Eastern Europe and Asia.
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