线蚓科隶属于环节动物门环带纲,迄今共记录32属650余种,是该纲的第二大科。它们广泛分布于土壤、海洋、淡水、河口和冰川等。其中,约2/3的线蚓科物种(近500种)为陆生种类,100余种仅分布在海洋中。尽管经历了200多年的探索,线蚓科仍然是认知最少的类群之一。尝试回顾人类对线蚓科环带动物分类学和系统发育学方面的认知历程和积累的知识体系,描述线蚓科关键的形态学分类特征以及线蚓科分类研究遇到的主要问题和障碍,展望了线蚓科分类学未来的研究方向。线蚓科的分类研究尚处于α分类阶段,体现在以物种探索为主和大量的已描述的物种需要验证等。而基于生物学物种概念(生殖隔离)的线蚓科物种探索,虽然有一些合理的逻辑解释,但缺乏严格的科学验证。线蚓科内多数属为复系,表明已建立的线蚓科分类系统仍然不能很好的反映线蚓科的自然进化历史。线蚓科分类面临的主要问题和障碍是未描述种类亟待发掘、已描述的物种需要验证、属/种的厘定以及现代属级概念的建立、DNA分类在线蚓科的应用和线蚓科内的系统发育关系研究亟待开展,以及物种探索的不平衡、经费和研究人才匮乏以及网络分类的缺失等。将分子学数据和系统发育物种概念纳入线蚓科的分类学研究,应该是线蚓科分类的一个方向。通过解读保守基因的信息,可以揭示线蚓科的祖先与它们生活的古环境长期斗争的历史,以及将优良的性状遗传给后代的过程和驱动力。而系统发育物种概念认为物种是拥有共同祖先的,物种仅能通过生殖隔离与系统发育重建一起加以验证。基于系统发育物种概念而构建的线蚓科分类系统,必将能真实的反映线蚓科内各分类单元的亲缘关系和进化轨迹。而将最新的线蚓科分类学知识传播于分类学知识的终端使用者,是线蚓分类学家的职责。这些知识将有助于提高人们对线蚓类在生态系统中功能的了解,如土壤有机质分解、养分矿化和健康评价以及评估气候变化等。

Enchytraeidae is the second largest family of the annelid class Clitellata, with nearly 650 species in 32 genera having been recognized up to now. These small but pretty potworms are almost cosmopolitan, being distributed in all major habitats including soils, oceans, fresh water, estuaries and glaciers, but with the majority of species being terrestrial (ca. 500) or marine (ca. 100). In spite of the long duration (over 200 years) of enchytraeid taxonomic investigation, the Enchytraeidae is still one of the most poorly-understood group of clitellates. Here, we provide an overview of the state of taxonomy and phylogenetics of the Enchytraeidae, then characterize its key morphological traits for enchytraeid identification, determine its main taxonomic problems and impediments, and provide future taxonomic and systematic perspectives. Firstly, enchytraeid systematics is still at its initial stage ( α taxonomy). This stage mainly concentrates on species exploration and validation. These species identification processes have been carried out through morphological analysis and consideration of the biological species concept. However, the high interspecific and/or intraspecific diversity of these traits, most of which are only observed and recorded in live condition, adds difficulty to enchytraeid identifications. Moreover, reproduction isolation of enchytraeids has rarely been tested, thus the hypothesis of established enchytraeid species in the biological species concept can not be confirmed. Second, phylogenetic studies of Enchytraeidae based on morphological-and-molecular data suggest that most of the enchytraeid genera are polyphyletic, indicating the established taxonomic systems yet do not genuinely reflect their evolutionary history. Thirdly, enchytraeid taxonomy faces such taxonomic problems and impediments as accelerating species exploration and testifying species validity, the establishment of genera/species definitions that reflect their real phylogenetic relationships, the application of DNA taxonomy to enchytraeid identification and reconstruction of intra-family phylogenies. Other impediments also constrain the develepment of enchytraeid taxonomy, such as the species-exploration imbalance across different regions of the world, the scarcity of funds and talented experts and the deficiency of electronically available taxonomic resources. Finally, we maintain that the application of both molecular data and the phylogenetic species concept should be the future direction of the enchytraeid taxonomy and systematics. Through reading the information stored in genes (such as COI gene), we can reconstruct the evolutionary history of enchytraeid ancestor struggling with their palaeoenvironment and the key processes and driving forces that enchytraeid ancestor had inherited their merit properties to their descendants. An enchytraeid taxonomic system based on the phylogenetic species concept should be tested and verified, e.g., by testing for reproductive isolation. Moreover, it is an important duty that enchytraeid experts disseminate advanced enchytraeid taxonomic knowledge to the public that can promote such enchytraeid-related research and recognitions of their roles in the processes of soil decomposition and nutrient mineralization, assessing soil ecosystem health condition, and evaluating global climate change.