One of the most peculiar groups of the mostly colonial phylum Bryozoa is the taxon Monobryozoon, whose name already implies non-colonial members of the phylum. Its peculiarity and highly unusual lifestyle as a meiobenthic clade living on sand grains has fascinated many biologists. In particular its systematic relationship to other bryozoans remains a mystery. Despite numerous searches for M. ambulans in its type locality Helgoland, a locality with a long-lasting marine station and tradition of numerous courses and workshops, it has never been reencountered until today. Here we report the first observations of this almost mythical species, Monobryozoon ambulans. For the first time since 1938, we present new modern, morphological analyses of this species as well as the first ever molecular data. Our detailed morphological analysis confirms most previous descriptions, but also ascertains the presence of special ambulatory polymorphic zooids. We consider these as bud anlagen that ultimately consecutively separate from the animal rendering it pseudo-colonial. The remaining morphological data show strong ties to alcyonidioidean ctenostome bryozoans. Our morphological data is in accordance with the phylogenomic analysis, which clusters it with species of Alcyonidium as a sister group to multiporate ctenostomes. Divergence time estimation and ancestral state reconstruction recover the solitary state of M. ambulans as a derived character that probably evolved in the Late Cretaceous. In this study, we also provide the entire mitogenome of M. ambulans, which—despite the momentary lack of comparable data—provides important data of a unique and rare species for comparative aspects in the future. We were able to provide first sequence data and modern morphological data for the unique bryozoan, M. ambulans, which are both supporting an alcyonidioidean relationship within ctenostome bryozoans.

中文翻译：

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重新发现不寻常的、孤独的苔藓动物 Monobryozoon ambulans Remane，1936：第一个分子和新的形态学数据阐明了其系统发育位置

苔藓虫门是苔藓虫门中最奇特的类群之一，它的名字已经暗示了该门的非殖民成员。作为生活在沙粒上的小型底栖动物分支，它的独特性和极不寻常的生活方式让许多生物学家着迷。特别是它与其他苔藓虫的系统关系仍然是个谜。尽管在其模式产地赫尔戈兰（赫尔戈兰）进行了大量搜寻，该地区拥有长期存在的海洋站并拥有众多课程和讲习班的传统，但直到今天才再次遇到它。在此，我们报告了对这种近乎神话的物种——游动单孢子虫（Monbryozoon ambulans）的首次观察。自 1938 年以来，我们首次提出对该物种的新的现代形态学分析以及第一个分子数据。我们详细的形态学分析证实了大多数先前的描述，但也确定了特殊的可移动多态动物的存在。我们认为这些是芽原基，最终连续地与动物分离，使其成为伪殖民地。其余的形态学数据显示与栉口动物苔藓虫有很强的联系。我们的形态学数据与系统发育分析一致，该分析将其与Alcyonidium物种聚类为多孔栉口动物的姐妹群。分歧时间估计和祖先状态重建恢复了 M. ambulans 的孤独状态，作为可能在白垩纪晚期进化的派生特征。在这项研究中，我们还提供了 M. ambulans 的完整线粒体基因组，尽管暂时缺乏可比数据，但为未来的比较方面提供了独特且稀有物种的重要数据。我们能够提供独特的苔藓虫 M. ambulans 的第一个序列数据和现代形态学数据，它们都支持栉口动物苔藓虫内的 Alcyonidioidean 关系。