The problematic calcareous microfossil Halysis is abundant in the Middle Ordovician Darriwilian Stage of the western edge of the Ordos Basin, North China. The rich and well-preserved specimens of Halysis in this area facilitate detailed studies for its skeletal construction and tube microstructure. Halysis differs from calcified cyanobacteria and calcareous red and green algae in morphology, skeletal construction and microstructure, as well as reproduction mode. Halysis typically consists of multiple juxtaposed parallel tubes arranged in sheets (‘multiple-tube’ type) or is just composed of one tube (‘single-tube’ type). In ‘multiple-tube’ Halysis , tube fission by bifurcation results from the insertion of a microcrystalline wall at the center of a mother tube. This study demonstrates for the first time that the tube walls of Halysis have a laminofibrous (fibronormal) microstructure, composed of fibrous calcite perpendicular to wall surface, and recognizes the ‘single-tube’ type Halysis composed of one tube; in addition, for the first time, this study finds out that ‘multiple-tube’ Halysis develops buddings from the conjunction of two tubes and ‘single-tube’ Halysis shows wide-angle Y-shaped branchings. Based on these findings, this study further compares Halysis with tabulate corals. Halysis appears stratigraphically earlier than Catenipora and Aulopora , and has a smaller tube size. ‘Multiple-tube’ Halysis resembles Catenipora and ‘single-tube’ Halysis resembles Aulopora in skeletal construction and microstructure, and in their tube walls of laminofibrous microstructure composed of fibrous calcite perpendicular to the tube wall surface. Catenipora and Halysis are both characterized by the absence of septal spines. The similarities suggest that Halysis may be the ancestor of Catenipora -like and Aulopora -like tabulate corals.

中文翻译：

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Halysis Høeg, 1932 — 来自华北鄂尔多斯盆地的一种祖先的板状珊瑚

在华北鄂尔多斯盆地西部边缘的中奥陶世 Darriwilian 阶，有问题的钙质微化石 Halysis 丰富。该地区丰富且保存完好的 Halysis 标本有助于对其骨骼结构和管状微观结构进行详细研究。Halysis在形态、骨骼结构和微观结构以及繁殖方式上不同于钙化蓝藻和钙质红绿藻。Halysis 通常由排列成片的多个并列平行管组成（“多管”型）或仅由一根管组成（“单管”型）。在“多管”Halysis 中，由于在母管中心插入微晶壁导致分叉导致管裂。本研究首次证明 Halysis 管壁具有层状纤维（纤维法向）微观结构，由垂直于壁面的纤维方解石组成，并识别出由一根管组成的“单管”型 Halysis；此外，本研究首次发现“多管”Halysis 由两根管子的连接发育出芽，“单管”Halysis 显示出广角Y 形分支。基于这些发现，本研究进一步将 Halysis 与平板珊瑚进行了比较。Halysis 在地层上出现的时间早于 Catenipora 和 Aulopora，并且管径较小。“多管”Halysis 在骨骼结构和微观结构上类似于 Catenipora，而“单管”Halysis 类似于 Aulopora，并且在它们的管壁中由垂直于管壁表面的纤维方解石组成的层状纤维微结构。Catenipora 和 Halysis 的特点都是没有隔刺。这些相似之处表明 Halysis 可能是类 Catenipora 和 Aulopora 类板状珊瑚的祖先。