Chengjiang fauna is one of the most important sources of early animal fossils. But how the soft tissues of these fossils were preserved is a mystery for long. Previous observations revealed that Chengjiang fossils are dominated by kerogen and pyrite crystals (Gabbott et al. 2004; Zhu et al. 2005) and three-dimensional ultrastructure is seldom reported. Here, we apply electron microscopy to study the preservation modes of weakly weathered Chengjiang fossils and found pyritized skin with submicron details in worm-like animals Cricocosmia jinningensis Hou & Sun, 1988 (Hou and Sun 1988). This new discovery proves that Chengjiang fossils can preserve three-dimensional submicron biological structures and rapid early pyritization is a key preservation mode of Burgess Shale-type Lagerstätten.

Pyrite,Chengjiang biota,integument,palaeoscolecids,taphonomy