Comparative sea spider neuroanatomy: exploring neural characters to illuminate phylogeny and evolution of an old arthropod lineage with limited morphological disparity

该项目的目的是比较成年神经解剖学的主要类群（“家庭”）的海洋Pycnogonida（海蜘蛛），以及示范研究成年神经发生在这个节肢动物谱系。作为所有其他螯形动物的姐妹群，密子虫是一个关键的分类群，当试图阐明螯形动物神经系统的进化时。现存的密锥虫显示出非常一致的身体组织，其特征是“头部”区域有三对特殊的附肢，躯干有四对行走的腿。然而，虽然步行腿结构是严格保守的，“头”的附属物显示出激烈的分类特异性变化。然而，无论是外部形态学，也没有分子序列数据迄今为止，使强大的重建密殖吸虫的生殖，内部解剖逾期审查。由于记录有用的神经特征的系统发育推断在主要节肢动物谱系的水平上，的pycnogonid中枢神经系统（CNS）是一个有前途的内部器官系统开始。使用现代技术（包括显微CT）3D重建的超细胞中枢神经系统结构将提供骨干研究在细胞水平上通过免疫标记的各种神经活性物质和随后的高分辨率成像。此外，体内细胞增殖实验加上基因表达研究和神经元回填将示范性地探索成人神经原性过程-一种未充分研究的现象，可能是许多节肢动物类群中特定CNS区域可塑性的基础。该项目将产生第一个数据矩阵的内部器官系统的密子虫，涵盖所有现存的家庭。分支系统学分析将（1）测试超细胞和细胞水平的神经特征在这个古老的节肢动物谱系中的实用性，具有有限的形态差异，（2）阐明神经和外部形态特征之间的潜在冲突，特别是在结构可变的“头”与保守的躯干，（3）允许分子pycnogonid的进化的关键评估。此外，神经解剖学特征的pycnogonid地面模式将被重建。通过与其他主要节肢动物谱系的比较，这将为螯肢动物和节肢动物神经系统的进化提供信息。除其他外，它是希望揭示额外的apomorphies-甚至分子-仍然不能令人满意地支持单门（Pycnogonida + Euchelicerata）。

This project aims to compare adult neuroanatomy across the major taxa (“families”) of the marine Pycnogonida (sea spiders), as well as to exemplarily study adult neurogenesis in this arthropod lineage. As likely sister group to all other chelicerates, pycnogonids are a pivotal taxon to consider, when trying to elucidate chelicerate nervous system evolution. Extant pycnogonids show a remarkably uniform body organization, featuring the “head” region with three specialized appendage pairs and the trunk with four walking leg pairs. However, while the walking leg structure is strictly conserved, the “head” appendages show drastic taxon-specific variations. Yet, neither external morphology, nor molecular sequence data have hitherto enabled robust reconstruction of pycnogonid phylogeny, rendering scrutiny of internal anatomy overdue. Owing to the documented usefulness of neural characters for phylogenetic inference at the level of major arthropod lineages, the pycnogonid central nervous system (CNS) is a promising internal organ system to begin with. Using modern-day techniques (incl. micro-CT) 3D-reconstruction of supracellular CNS structures will provide the backbone for studies at the cell level via immunolabeling of various neuroactive substances and subsequent high-resolution imaging. Additionally, in-vivo cell proliferation experiments coupled with gene expression studies and neuronal backfills will exemplarily explore adult neurogenic processes – an understudied phenomenon that may underlie plasticity of specific CNS areas in many arthropod taxa. The project will result in the first data matrix for an internal organ system of Pycnogonida, covering all extant families. Cladistic analyses will (1) test the utility of supracellular and cell-level neural characters in this old arthropod lineage with limited morphological disparity, (2) illuminate potential conflicts between neural and external morphological characters, especially in the structurally variable “head” versus the conserved trunk, and (3) allow critical evaluation of molecular pycnogonid phylogenies. Further, neuroanatomical features of the pycnogonid ground pattern will be reconstructed. Via comparison to other major arthropod lineages, this will inform on chelicerate and arthropod nervous system evolution. Among others, it is hoped to reveal additional apomorphies of the – even molecularly – still unsatisfactorily supported monophylum (Pycnogonida + Euchelicerata).