A strongly divergent lineage, putatively a new cryptic species, of colonial ascidian was first detected as an anomalous sample in a population genomics study of the well-known worldwide invasive species Didemnum vexillum Kott, 2002. This putative new taxon, found in a marina in Roscoff, France, is indistinguishable from Didemnum vexillum in the external aspect and coexists with it in syntopy. However, morphological characters such as spicules and larvae allow a clear-cut distinction. In accordance with the preliminary results based on genome-wide analyses, morphological traits and mitochondrial sequences of the cytochrome oxidase I gene both support the establishment of a new species Didemnum pseudovexillum sp. nov. Previous unidentified sequences in public databases showed that the new species is also present in NW Mediterranean marinas. Didemnum pseudovexillum sp. nov. is assigned for the time being a cryptogenic species status, although its presently known disjoint distribution across two biogeographic regions and its presence in ports are suggestive of an introduced species. Further studies should be performed to ascertain its current distribution and putative natural range and settle its native vs. non-native status. This finding casts doubts on previous reports of Didemnum vexillum and also calls for caution when performing fast field surveys of non-indigenous species such as rapid assessment surveys (RAS) or BioBlitz surveys, based solely on external characters.

中文翻译：

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外观可能具有欺骗性：Didemnum pseudovexillum sp.。十一月 （Ascidiacea）在欧洲港口

在2002年对全球著名入侵物种Didemnum vexillum Kott进行的种群基因组学研究中，首先发现了一个强烈不同的殖民地海鞘谱系，即一个新的隐性物种，这是一个异常样品。法国的罗斯科夫（Roscoff）在外观上与Didemnum vexillum没什么区别，并与它并存。但是，形态特征（例如针状幼虫和幼虫）可以清楚地区分。根据基于全基因组分析的初步结果，细胞色素氧化酶I基因的形态特征和线粒体序列均支持建立新物种Didemnum pseudovexillumsp。十一月 公共数据库中以前未确认的序列表明，新物种也出现在西北地中海码头。Didemnum pseudovexillum sp。十一月 尽管目前已知其在两个生物地理区域内的不相交分布以及其在港口中的存在暗示了引入的物种，但暂时将其分配为隐源物种状态。应该进行进一步的研究以确定其当前分布和假定的自然范围，并解决其自然状态与非自然状态。这一发现使人们对以前的Dedemnum vexillum报告产生怀疑，并且在对非本地物种进行快速野外调查（例如仅基于外部特征的快速评估调查（RAS）或BioBlitz调查）时也要谨慎。