Institute of Geology, Adam Mickiewicz University, Poznań, Poland.
Faculty of Geology, University of Warsaw, Warsaw, Poland.
PLoS One. 2021 Sep 29;16(9):e0257523. doi: 10.1371/journal.pone.0257523. eCollection 2021.
Heterocorals represent an enigmatic group of Palaeozoic corals, known from relatively short time intervals in the Devonian and Carboniferous periods. The major differences between Heterocorallia and other Palaeozoic corals are the lack of an external theca (epitheca), lack of calices and the presence of dichotomously dividing septa-like structures. Heterocoral skeleton was presumably externally covered by the soft tissue and each branch of their skeleton has, until now, been regarded as a corallite-a skeleton of a single polyp. We investigated upper Famennian Oligophylloides from Morocco, focussing on branching processes, wall structure, previously poorly known initial growth stages and the growing tip, described here for the first time. We demonstrate that Oligophylloides shows a unique colony development not known in any group of anthozoans possessing a septate-like architecture and suggest that the previously postulated homology between true septa in hexa- and rugose corals on one hand, and Oligophylloides on the other, must be rejected. Based on the skeleton structure and branching patterns, we postulate, contrary to former ideas, that the stem and branches of heterocorals represent the skeleton of a multi-polyp colonial coral, similar to many extant octocorals. We found numerous potential homologies with octocoral skeletons (notably the Keratoisidinae within the Isididae) and, as a result, we propose the inclusion of the order Heterocorallia within the subclass Octocorallia. This suggestion requires, however, further research on the other taxa of heterocorals. We also propose some changes to the morphological terminology for the Heterocorallia.
异珊瑚是古生代珊瑚的一个神秘群体，仅知其存在于泥盆纪和石炭纪相对较短的时间间隔内。异珊瑚与其他古生代珊瑚的主要区别在于缺乏外部壳（表皮）、缺乏萼和存在二分叉的类似隔膜的结构。异珊瑚骨骼可能被软组织覆盖，其骨骼的每个分支迄今为止一直被视为一个珊瑚虫腔——单个珊瑚虫的骨骼。我们研究了来自摩洛哥的上泥盆统 Oligophylloides，重点研究了分枝过程、壁结构、以前知之甚少的初始生长阶段和生长尖端，这是首次对此进行描述。我们证明，Oligophylloides 表现出一种独特的群体发育，在具有类似隔膜结构的任何一个群体的珊瑚虫中都没有发现，并且表明以前在六放珊瑚和皱珊瑚中的真正隔膜以及 Oligophylloides 之间假定的同源性必须被拒绝。基于骨骼结构和分枝模式，我们提出与以前的观点相反的观点，即异珊瑚的茎和分枝代表多珊瑚群体珊瑚的骨骼，类似于许多现存的八放珊瑚。我们发现了与八放珊瑚骨骼的许多潜在同源性（特别是在 Isididae 中的 Keratoisidinae），因此，我们建议将 Heterocorallia 目归入八放珊瑚亚纲。然而，这一建议需要对异珊瑚的其他分类群进行进一步研究。我们还建议对异珊瑚的形态学术语进行一些更改。
