Figure 4 — Mouth apparatuses of two Cambrian fossils. Left, the anomalocaridid euarthropod Hurdia has a mouth surrounded with a ring of plates, and a throat lined with tooth-plates. Right, the penis worm Ottoia has an eversible throat lined with teeth, with a single ring of spines marking the official mouth. Abbreviations: m.pl., Mouth plates; t.t., throat teeth. Image credits: Marianne Collins; A. C. Daley, G. E. Budd and J.-B. Caron Journal of Systematic Palaeontology 11, 743–787 (2013). DOI 10.1080/14772019.2012.732723; Martin Smith/Smithsonian Institution.