Annelids possessing a posterior sucker and a fixed number of somites – most famously leeches (Hirudinida), but also crayfish worms (Branchiobdellida) and salmonid parasites (Acanthobdellida) - form a clade; however, determining the relationships between these orders has proven challenging. Here, we compile the largest molecular phylogenetic dataset yet analysed for these groups, including new sequences for key taxa. We find robust model-based support for a clade formed by Hirudinida and Acanthobdellida, contrasting the largest prior studies. We determine that conflicting prior studies included contaminant sequences for Acanthobdella peledina. In addition to this broad-scale comparison, the size of our dataset grants us invaluable insight into the internal relationships of leeches and crayfish worms. Of particular importance, a largely marine clade of leeches (Piscicolidae and Ozobranchidae) is recovered as sister to all remaining Hirudinida. This necessitates the dissolution of the paraphyletic suborder Rhynchobdellida into two new suborders (Oceanobdelliformes and Glossiphoniiformes). Likewise, we decompose Arhynchobdellida into its respective suborders: Hirudiniformes, Erpobdelliformes, and the new, monotypic, Americobdelliformes.

具有后部吸盘和一定数量的体节的后足动物-最著名的是水（Hirudinida），还有小龙虾蠕虫（Branchiobdellida）和鲑鱼寄生虫（Acanthobdellida）-形成进化枝。但是，确定这些订单之间的关系已证明具有挑战性。在这里，我们编译了尚未对这些组进行分析的最大分子系统发育数据集，包括关键分类单元的新序列。我们找到了由Hirudinida和Acanthobdellida形成的进化枝的基于模型的强大支持，这与最大的先前研究形成了鲜明对比。我们确定先前的研究相互矛盾，包括了Acanthobdella peledina的污染序列。除了进行大规模的比较之外，我们的数据集还使我们对水ches和小龙虾蠕虫的内部关系具有不可估量的洞察力。尤为重要的是，回收了大部分的海洋水of（Pi科和O科），作为其余所有水rud科的姊妹。这就需要将副生亚目Rhynchobdellida分解为两个新的亚目（Oceanobdelliformes和Glossiphoniiformes）。同样，我们将伞形目分解为各自的子顺序：Hi形目，叶形目和新的单型形目形。