This work aimed to test whether the colour variability featured by the European nudibranch Polycera quadrilineata is consistent with the concept of a single polychromatic species or may hide multiple lineages. Samples from across the geographic range of P. quadrilineata together with representatives from worldwide species with a focus on Atlantic diversity, were gathered and studied using an integrative taxonomic approach. Morpho-anatomical characters were investigated by light and scanning electron microscopy. Bayesian molecular phylogenetics using MrBayes, the Automatic Barcode Gap Discovery species delimitation method, and haplotype network analysis using the PopArt software were employed to help delimit species using the mitochondrial gene cytochrome c oxidase subunit I (COI). The results supported the existence of a second species, here described and named Polycera norvegica sp. nov., only known from Norway where it is sympatric with P. quadrilineata. The COI uncorrected p-genetic distance between the two species was estimated at 9.6–12.4%. Polycera norvegica sp. nov. differs by exhibiting a black dotted or patchy dotted pattern occasionally with more or less defined orange/brown patches, but never black continuous or dashed stripes as in P. quadrilineata. The two species share a common colouration with a whitish base and yellow/orange tubercles. Anatomically, P. norvegica sp. nov. has a weaker labial cuticle, a smaller radula with fewer rows, and only four marginal teeth, a reproductive system with a single lobed bursa copulatrix, shorter reproductive ducts, and a penis armed with two kinds of spines: needle-like and hook-shaped penile spines.

中文翻译：

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综合分类学揭示了欧洲水域中一种神秘的海蛞蝓属 Polycera (Polyceridae)

这项工作旨在测试欧洲裸鳃亚目是否具有颜色变异性四线蕨与单一多色物种的概念一致或可能隐藏多个谱系。来自不同地理范围的样本P. quadrilineata与来自世界各地以大西洋多样性为重点的物种的代表一起，使用综合分类学方法收集和研究。通过光学和扫描电子显微镜研究形态解剖特征。使用 MrBayes 的贝叶斯分子系统发育、自动条形码间隙发现物种定界方法和使用 PopArt 软件的单倍型网络分析被用来帮助使用线粒体基因细胞色素定界物种C氧化酶亚基 I (COI)。结果支持第二个物种的存在，这里描述和命名多毛蓼sp。十一月，仅在与它同域的挪威知道P. quadrilineata. 未修正的 COIp两个物种之间的遗传距离估计为 9.6-12.4%。多毛蓼sp。十一月 不同之处在于呈现黑色点状或斑片状点状图案，偶尔带有或多或少清晰的橙色/棕色斑块，但绝不会出现黑色连续或虚线条纹，如P. quadrilineata. 这两个物种有一个共同的颜色，带有白色的基部和黄色/橙色的结节。在解剖学上，P. norvegicasp。十一月 阴唇角质层较弱，齿部较小，行数较少，只有四颗边缘牙齿，生殖系统有一个单裂的交联囊，生殖管较短，阴茎有两种刺：针状和钩状阴茎刺。