Saccorhytus is an early ecdysozoan and not the earliest deuterostome.

The early history of deuterostomes, the group composed of the chordates, echinoderms and hemichordates 1 , is still controversial, not least because of a paucity of stem representatives of these clades 2-5 . The early Cambrian microscopic animal Saccorhytus coronarius was interpreted as an early deuterostome on the basis of purported pharyngeal openings, providing evidence for a meiofaunal ancestry 6 and an explanation for the temporal mismatch between palaeontological and molecular clock timescales of animal evolution 6-8 . Here we report new material of S. coronarius, which is reconstructed as a millimetric and ellipsoidal meiobenthic animal with spinose armour and a terminal mouth but no anus. Purported pharyngeal openings in support of the deuterostome hypothesis 6 are shown to be taphonomic artefacts. Phylogenetic analyses indicate that S. coronarius belongs to total-group Ecdysozoa, expanding the morphological disparity and ecological diversity of early Cambrian ecdysozoans.