Palaeoscolecids from the early Cambrian Guanshan biota, Yunnan Province, China

Palaeoscolecidomorphs (Palaeoscolecida and Cricocosmiidae) are widespread early Palaeozoic worms crucial to understanding the early evolution of Ecdysozoa. They are well known from the early–middle Cambrian of the Yangtze Platform of South China, but research has disproportionately focused on the well‐known Cambrian Stage 3 Chengjiang biota of Yunnan Province. Here, palaeoscolecid specimens from the Cambrian Stage 4 Guanshan biota are described, collected from a new locality in Yunnan's Fumin county. A new species of Guanduscolex Hu et al . ( Guanduscolex hexagonus ) is described , and species of Wronascolex Ivantsov & Zhuravlev, and Wudingscolex Hu et al . are revised. This facilitates a comparative discussion of the two faunas that is not yet possible between other Cambrian soft‐bodied biotas of the Yangtze Platform. Although they are close in age and occur in the same region, the Guanshan and Chengjiang palaeoscolecidomorph faunas are highly distinct from each other. This suggests the possibility of a faunal turnover, at least locally, between Cambrian Stages 3 and 4 marked by the appearance of long‐lived palaeoscolecid clades with more densely ornamented and tightly regimented plates (including Wronascolex (Cambrian Series 2 to Late Ordovician) and possibly Palaeoscolecidae (Cambrian Series 2 to Ludlow)) and the disappearance of cricocosmiids. Furthermore, the phylogenetically critical ventral projections are illustrated in Wudingscolex , and their significance and context are summarized. This shows that serially repeated ventral projections are present in palaeoscolecidomorph taxa outside Chengjiang and across a range of taxa; they are probably an ancestral character for palaeoscolecidomorphs, regardless of the monophyly of the group.