Koltzov Institute of Developmental Biology, Moscow, Russia.
Zoological Museum of the Moscow State University, Moscow, Russia.
PLoS One. 2020 Nov 20;15(11):e0242103. doi: 10.1371/journal.pone.0242103. eCollection 2020.
Nudibranch molluscs of the family Tritoniidae are widely used neuroscience model systems for understand the behavioural and genetic bases of learning and memory. However species identity and genus-level taxonomic assignment of the tritoniids remain contested. Herein we present a taxonomic review of the family Tritoniidae using integration of molecular phylogenetic analysis, morphological and biogeographical data. For the first time the identity of the model species Tritonia tetraquetra (Pallas, 1788) and Tritonia exsulans Bergh, 1894 is confirmed. T. tetraquetra distributes across the large geographic and bathymetric distances in the North-Eastern (NE) and North-Western (NW) Pacific. In turn, at NE Pacific coasts the separate species T. exsulans is commonly occured. Thus, it reveals a misidentification of T. tetraquetra and T. exsulans species in neuroscience applications. Presence of more hidden lineages within NW Pacific T. tetraquetra is suggested. The long lasting confusion over identity of the species from the genera Tritonia and Tochuina is resolved using molecular and morphological data. We also disprove a common indication about "edible T. tetraquetra" at the Kuril Islands. It is shown that Tochuina possesses specialized tritoniid features and also some characters of "arminacean nudibranchs", such as Doridoxa and Heterodoris. Diagnoses for the families Doridoxidae and Heterodorididae are provided. Taxonomy of the genus Doridoxa is clarified and molecular data for the genus Heterodoris presented for the first time. A taxonomic synopsis for the family Tritoniidae is provided. A new genus among tritoniid taxa is proposed. Importance of the ontogeny-based taxonomy is highlighted. The cases when apomorphic characters considerably modified in a crown group due to the paedomorphosis are revealed. Tracing of the character evolution is presented for secondary gills-a key external feature of the family Tritoniidae and traditional dendronotacean nudibranchs.
涡虫软体动物是一种广泛应用于神经科学模型系统的生物，用于理解学习和记忆的行为和遗传基础。然而，涡虫的物种身份和属级分类仍然存在争议。本文利用分子系统发育分析、形态学和生物地理学数据，对涡虫科进行了分类学综述。首次确认了模型物种 Tetraquetra （Pallas，1788）和 Tritonia exsulans Bergh，1894 的身份。Tetraquetra 分布在东北太平洋和西北太平洋的广阔地理和水深距离内。相反，在东北太平洋海岸，通常会出现单独的物种 Tritonia exsulans。因此，这揭示了神经科学应用中对 Tetraquetra 和 Tritonia exsulans 物种的错误鉴定。在西北太平洋的 Tetraquetra 中，可能存在更多隐藏的谱系。利用分子和形态学数据解决了 Tritonia 和 Tochuina 属物种身份长期以来的混淆。我们还反驳了关于千岛群岛“可食用 Tetraquetra”的常见说法。结果表明，Tochuina 具有特化的涡虫特征，也具有一些“armina 类扁形动物”的特征，如 Doridoxa 和 Heterodoris。提供了 Doridoxidae 和 Heterodorididae 科的诊断。澄清了 Doridoxa 属的分类，并首次提供了 Heterodoris 属的分子数据。提供了涡虫科的分类概要。提出了涡虫科中的一个新属。强调了基于个体发生的分类学的重要性。揭示了由于幼态持续而导致冠群中特化特征发生显著变化的情况。展示了次生鳃的特征进化，次生鳃是涡虫科和传统的 dendronotacean 扁形动物的关键外部特征。
