From the snails in your garden to giant squid that wrestle with sperm whales, the molluscs are one of the most disparate and successful animal phyla. But because they evolved rapidly in the Cambrian period, some 500 million years ago, there is still much debate about their early history — in particular, what the earliest molluscs looked like. A fossil from the Ordovician Fezouata formation in Morocco (known for relic Burgess-Shales-type animals) might shed light on the issue. The creature is a flattened slug-like animal with a distinct, single shell on its head, the rest of the body being covered with spines. The exciting part is that the animal has a radula, the distinctive rasping tongue that is a defining character for molluscs and is the reason slugs can demolish your lettuces so effectively. This phylogenetic analysis shows that the newly discovered creature groups with some other forms variously classified as either molluscs, stem brachiopods or similar, but places it within the molluscs, at the base of the Aculifera (the multiple-shelled chitons plus the shell-free aplacophora), as opposed to the Conchifera (all other molluscs). This finding suggests that early molluscs had only a single shell.
- Ancestral morphology of crown-group molluscs revealed by a new Ordovician stem aculiferan (Letter p471, doi: 10.1038/nature21055)
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