Cnidarians are early‐diverging metazoans, but evolutionary aspects of some taxa are still poorly understood, as in the order Zoantharia (Anthozoa: Hexacorallia). Zoantharians have been divided into two suborders based on the arrangement of the fifth septae as complete (Macrocnemina) or incomplete (Brachycnemina). Previous molecular phylogenetic analyses have indicated the need for re‐evaluation as Macrocnemina has been found to be paraphyletic. Despite many phylogenetic studies, the recovery of complete mitochondrial genomes (mt‐genomes) for systematic and evolutionary studies of zoantharians has been limited. The present study represents the first to sequence the complete mt‐genomes of members of eight of nine zoantharian families. Although all examined mt‐genomes had the same gene order arrangement, there were variations among mt‐genomes' sizes, nucleotide substitution rates, and introns. Only two species did not have the cox1 intron, which harbors a gene coding a homing endonuclease of the LAGLIDADG type. Our mitogenomic analyses also showed relatively high nucleotide diversity in mt‐DNA regions other than the standard regions traditionally considered for DNA barcoding of this group. Phylogenetic analyses using 13 mt‐genome protein‐coding genes recovered a fully resolved tree with clear separation between macrocnemic representatives. Ancestral state reconstruction analyses revealed three main transitions in arrangement of the marginal musculature through the evolutionary history of the order. An “early” transition from reticulate mesogleal to a cteniform endodermal arrangement was followed by transitions that occurred in the common ancestor of the Brachycnemina and family Hydrozoanthidae. Our results indicate the need for clarification of higher‐level phylogeny and taxonomy of Zoantharia.

中文翻译：

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整个线虫区系中完整线粒体基因组分析的进化意义（Cindaria：Hexacorallia）

头足类动物是早期分化的后生动物，但对某些分类群的进化方面仍然知之甚少，例如按带状花椒（Anzozoa：Hexacorallia）的顺序。根据第五个隔片的排列，Zoantharians被分为两个子顺序：完整（Macrocnemina）或不完整（Brachycnemina）。先前的分子系统发育分析表明需要重新评估，因为已经发现Macroncnemina是副生的。尽管进行了许多系统进化研究，但对线虫动物进行系统和进化研究的完整线粒体基因组（mt-基因组）的恢复仍然受到限制。本研究代表了第一个对9个zoantharian家庭中的8个成员的完整mt基因组进行测序的研究。尽管所有检查的mt基因组均具有相同的基因顺序排列，但mt基因组之间存在差异 大小，核苷酸取代率和内含子。只有两个物种没有考克斯1内含子，其包含编码LAGLIDADG型归巢核酸内切酶的基因。我们的线粒体基因组分析还显示，除了传统上考虑该组DNA条形码的标准区域外，mt-DNA区域中的核苷酸多样性相对较高。使用13个mt基因组蛋白质编码基因的系统发育分析恢复了完整的树，并在大流行代表之间明确分离。祖先状态重建分析揭示了通过阶的进化史，边缘肌肉组织排列的三个主要转变。从网状的中胚层到网状的内胚层排列的“早期”转变之后，发生在短臂目和家蝇科的共同祖先中。