Phylogenetic analysis of phenotypic characters and evolutionary transformations in Appendicularia (= Larvacea) and their consequences for the reconstruction of the groundplan of Chordata

脊索动物包括三个单系动物分类群：被毛类(=被囊类)、钩吻类(=头索动物)和脊椎动物(=头盖纲)。大约有2700个物种，被囊类显示出令人眼花缭乱的生活史策略和身体计划的多样性；许多物种以固着生物的形式生活在底物上，其他物种自由地漂浮在浮游生物中，有些物种在世代之间表现出惊人的多态。最近的系统发育和基于形态的系统发育一致地将附属目(=幼虫纲)定位为其余被囊类的姊妹群。这使得大约有70个物种的附属藻处于一个关键位置来阐明被囊进化，因为原始特征可以预期优先发生在附属物动物中。现代的形态研究几乎完全局限于一个物种--Oikopleura dioica--阻碍了对这一在系统发育上具有重要意义的动物群体内差异的可靠评估。对于深海Bathochordaeus属的成员，甚至连光学显微镜下的现代研究都不存在。最近的系统发育分析只包括一个附属物物种，基于18S rDNA序列的较早的分子系统发育包括多达一个科的三个物种。在拟议的项目中，将对这三个科的13个附属物物种的标本进行详细的形态分析。一个主要目标是根据数字解剖学和免疫组织学分析，结合共聚焦激光扫描显微镜，形成用于分支分析的数据矩阵。只要有可能，这些分析将得到透射电子显微镜研究的补充。这样，将实现以下目标：(1)将根据现代标准对该关键分类群的形态差异进行采样和记录。(2)将制定最大特征数的初级同源性假设。(3)首次，(4)器官系统的功能形态假说可以基于超微结构分析提出。(5)进化转化将在所有器官系统中被重复地解释。(6)附属目最后一个共同祖先的基本格局的分支重建将被实现。(7)对更高级分类单元的进化场景的影响将被讨论。

Chordata comprises three monophyletic animal taxa: tunicates (= Tunicata), lancelets (= Cephalochordata), and vertebrates (= Craniota). With approximately 2700 species, tunicates show a bewildering diversity of life-history strategies and body plans; many species live attached to the substrate as sessile organisms, others float freely in the plankton, and some display spectacular polymorphisms between generations. Recent phylogenomic and morphology-based phylogenies concur in positioning Appendicularia (= Larvacea) as sister group to the remaining tunicates. This puts Appendicularia with approximately 70 species in a key position to elucidate tunicate evolution, because primitive traits can be expected to occur preferentially in appendicularians. Modern morphological studies are almost exclusively restricted to one species – Oikopleura dioica – impeding a reliable assessment of the disparity within this phylogenetically important group of animals. For the members within the deep-sea genus Bathochordaeus not even light microscopical modern investigations exist. The recent phylogenomic analyses comprise but a single appendicularian species, older molecular phylogenies based on 18S rDNA-sequences included up to three species of a single family. In the proposed project specimens of 13 appendicularian species of all three families will be morphologically analyzed in detail. A major goal is the conceptualization of a data matrix for cladistic analysis based on digital anatomies and immunohistological analyses combined with confocal laser scanning microscopy. Wherever possible, these analyses will be complemented by transmission electron microscopic investigation. In this way, the following goals will be achieved:(1) The morphological disparity of this key taxon will be sampled and documented according to modern standards.(2) Primary homology hypotheses of a maximum number of characters will be formulated.(3) For the first time, a morphology based phylogenetic hypothesis based on a transparent cladistic analysis will be suggested.(4) Hypotheses of the functional morphology of organ systems can be proposed based on the ultrastructural analyses.(5) Evolutionary transformations will be reproducibly explained in all organ systems.(6) A cladistic reconstruction of the ground pattern in the last common ancestor of Appendicularia will be achieved.(7) Implications for evolutionary scenarios of higher taxa Tunicata, Olfactores (= Tunicata + Craniota), and Chordata grounded in these cladistic analyses will be discussed.