The power of combined molecular and morphological analyses for the genus <i>Botrylloides</i>: identification of a potentially global invasive ascidian and description of a new species

Botryllids are colonial styelid ascidians for which morphological characters distinguishing genera and species are often difficult to identify and frequently ambiguous. <i>Botrylloides perspicuus</i>, <i>Botrylloides giganteus</i>, and <i>Botrylloides pizoni</i> have similar colony and zooid appearances and over recent years have been found in dispersed localities around the world. In order to determine how many valid <i>Botrylloides</i> species there are, and how they are geographically distributed, we performed both molecular and morphological analyses on fresh and archival museum specimens of these <i>Botrylloides</i> coming from six distant localities: southern Italy, southern California, Brazil, Galapagos Islands, New Zealand, and Australia. Moreover, we re-analysed the morphology of a number of formalin-preserved museum specimens. We concluded that both <i>B. perspicuus</i> and <i>B. giganteus</i> are indeed valid species and report morphological and molecular characters that distinguish these species; <i>B. pizoni</i> is concluded to be a junior synonym of <i>B. giganteus</i>. The geographic distribution, collection dates, and growth substrates of <i>B. giganteus</i> indicate that this species is rapidly spreading worldwide and has traits that may enhance invasiveness (i.e., presence in intertidal regions; high tolerance to air exposure, temperature and salinity variation). Therefore, <i>B. giganteus</i> should be a focus of both researchers and managers concerned with marine biosecurity. Interestingly, the morphological re-analyses of archival museum samples guided by molecular results, led to the taxonomic reassignment of several botryllid specimens as well as to the identification of a new species, <i>Botrylloides conchyliatus</i> sp. nov., which is here described. http://www.zoobank.org/urn:lsid:zoobank.org:pub:0D896E42-F460-45E2-B74C-576A011D9214

葡萄海鞘科物种均为群栖性茎海鞘，其用于区分属与种的形态学特征往往难以辨识，且常存在歧义。*Botrylloides perspicuus*、*Botrylloides giganteus*及*Botrylloides pizoni*的群体形态与个员外观高度相似，近年来在全球多个分散的采样区域均有发现。为明确有效葡萄茎海鞘属（*Botrylloides*）物种数量及其地理分布格局，研究团队对采自6个远隔区域——意大利南部、加利福尼亚南部、巴西、加拉帕戈斯群岛、新西兰与澳大利亚——的新鲜样本及馆藏博物馆标本，开展了分子与形态学综合分析。此外，本研究还对多份福尔马林固定的馆藏博物馆标本的形态特征进行了重新检视与分析。研究结果证实，*B. perspicuus*与*B. giganteus*均为有效物种，并明确了可用于区分二者的形态学与分子学特征；同时认定*B. pizoni*为*B. giganteus*的次定同物异名。*B. giganteus*的地理分布范围、采集时间及附着基质特征显示，该物种正快速在全球范围内扩散，且具备多项可能增强其入侵性的性状：例如可栖息于潮间带区域，对空气暴露、温度及盐度波动具有较高耐受性。因此，*B. giganteus*应成为海洋生物安全领域研究者与管理者共同关注的重点物种。值得注意的是，依托分子分析结果对馆藏标本开展的形态学重新分析，不仅完成了多份葡萄海鞘科标本的分类学重归类，还发现并描述了一个新物种——*Botrylloides conchyliatus* sp. nov.。http://www.zoobank.org/urn:lsid:zoobank.org:pub:0D896E42-F460-45E2-B74C-576A011D9214