The burrow dwelling behavior and locomotion of palaeoscolecidian worms: New fossil evidence from the Cambrian Chengjiang fauna

• The life habits of palaeoscolecidian worms are greatly updated;
• Some previously reported burrow dwelling behavior of palaeoscolecidians are mis-identified;
• Different palaeoscolecidians have different life habits;
• Palaeoscolecidians are all burrow dwellers and temporarily crawled on the sea beds.

Palaeoscolecidian worms are abundant components in Paleozoic shallow marine communities; however, their life habits remain poorly known. Here we present evidence of burrow dwelling behavior of palaeoscolecidian worms based on well-preserved specimens of Cricocosmia jinningensis and Mafangscolex sinensis from the lower Cambrian Maotianshan Shale. C. jinningensis was found living within elongate burrows, either of cylindrical or more rarely of swollen sac-like shape, while M. sinensis lived in elongate and slender tube-like burrows. The wall of the burrow has a sharp boundary from the surrounding sediment, which may have been consolidated by the worm itself and it resembles the recent priapulid worm Maccabeus. It is demonstrated that M. sinensis makes a snake-twisting movement in its burrow that differs from crawling behavior of C. jinningensis by the use of two rows of lateral plates. The lined burrows of Maotianshania cylindrica previously reported are in fact made by C. jinningensis and M. sinensis.