Annelids are among the most disparate animal phyla, encompassing ambush predators, suspension feeders and terrestrial earthworms1. Early annelid evolution remains obscure or controversial2,3 , partly due to discordance between molecular phylogenies and fossils2,4. Cambrian annelid fossils have morphologies indicating epibenthic lifestyles, whereas phylogenomics recovers sessile, infaunal and tubicolous taxa as an early diverging grade5. Magelonidae and Oweniidae (Palaeoannelida1 28) are the sister group of all other annelids but contrast with Cambrian taxa in both lifestyle and gross
morphology2,6. We describe a new fossil polychaete, Dannychaeta tucolus, from the early Cambrian Canglangpu Formation7, preserved within delicate, originally organic dwelling tubes. The head has a well-defined spade-shaped prostomium with elongate ventrolateral palps. The body has a wide, stout thorax and elongate abdomen with biramous parapodia with parapodial lamellae. This character combination is shared with extant Magelonidae, and phylogenetic analyses recover Dannychaeta within Palaeoannelida. Dannychaeta is the oldest polychaete unambiguously belonging inside crown annelids, providing a constraint on the tempo of annelid evolution and revealing unrecognised ecological and morphological diversity in ancient annelids.
