The Microsporidia, an often overlooked fungal lineage, exhibit increasing diversity and taxonomic understanding with the use of genomic techniques. They are obligate parasites infecting a diversity of hosts, including crustaceans. Crustacea are, in essence, ancient insects and their relationship with the Microsporidia is both diverse and convoluted. Relationships between crayfish and their microsporidian parasites display geospatial and taxonomic diversity. Through classical (histological, ultrastructural, developmental) and genomic (phylogenetic, phylogenomic) approaches, we expand the known diversity of crayfish-infecting microsporidia into the genus Nosema by describing three novel species from North America: Nosema astafloridana n. sp. infecting Procambarus pictus and Procambarus spiculifer, Nosema rusticus n. sp. infecting Faxonius rusticus, and Nosema wisconsinii n. sp. infecting Faxonius propinquus and Faxonius virilis. Additionally, we provide SSU sequence data for further Nosema diversity from Procambarus clarkii and Pacifasticus gambelii. The taxonomy of aquatic crustacean-infecting Nosema have been under scrutiny among microsporidiologists—using genomic data we solidify this systematic relationship. Our genomic data reveal phylogenomic divergence between terrestrial insect-infecting Nosema and aquatic crustacean-infecting Nosema but place our novel species within the Nosema. Comparative genomic analysis reveal that Nosema rusticus n. sp. is a tetraploid organism, making this the first known polyploid from the genus Nosema. Annotation of the genomic data highlight that crayfish-infecting Nosema have distinct proteomic differences when compared to amphipod and insect-infecting microsporidians. Alongside the new diversity uncovered and genome-supported systematics, we consider the role of these new ‘invasive’ parasites in biological invasion systems, exploring their relationship with their invasive hosts.

小孢子虫是一种经常被忽视的真菌谱系，通过使用基因组技术表现出越来越多的多样性和分类学理解。它们是专性寄生虫，感染多种宿主，包括甲壳类动物。甲壳类动物本质上是古老的昆虫，它们与 Microsporidia 的关系既多样又复杂。小龙虾与其微孢子虫寄生虫之间的关系显示了地理空间和分类学的多样性。通过经典（组织学、超微结构、发育）和基因组（系统发育、系统发育）方法，我们通过描述来自北美的三个新物种，将已知的感染小龙虾的小孢子虫的多样性扩展到 Nosema 属：感染 Procambarus pictus 和 Procambarus spiculifer 的 Nosema astafloridana n. sp.、感染 Faxonius rusticus 的 Nosema rusticus n. sp. 和 Nosema wisconsiniin. sp. 感染 Faxonius propinquus 和 Faxonius virilis。此外，我们还提供了来自 Procambarus clarkii 和 Pacifasticus gambelii 的 Nosema 多样性的 SSU 序列数据。感染水生甲壳类动物的 Nosema 的分类学一直受到微孢子虫学家的审查——使用基因组数据，我们巩固了这种系统关系。我们的基因组数据揭示了感染陆生昆虫的 Nosema 和感染水生甲壳类动物的 Nosema 之间的系统发育差异，但将我们的新物种置于 Nosema 中。比较基因组分析表明，Nosema rusticus n. sp. 是一种四倍体生物，使其成为 Nosema 属的第一个已知多倍体生物。 基因组数据的注释强调，与片足类和昆虫感染的微孢子虫相比，感染小龙虾的 Nosema 具有明显的蛋白质组学差异。除了发现新的多样性和基因组支持的系统学外，我们还考虑了这些新的“侵入性”寄生虫在生物入侵系统中的作用，探索它们与入侵宿主的关系。