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Paleontologists found a fossil of the ancestor of modern molluscs, which instead of a shell had the appearance of an external skeleton made of conical mineralized spines, writes Success in UA.
Because of this, the mollusk found in China was named Shishania aculeata, i.e. thorny shishania. It lived in the Cambrian period about 500 million years ago, and scientists believe it gave rise to both shell-like molluscs and rarer exoskeleton molluscs, such as chitons, reports nauka.ua.
In structure, Shishania aculeata resembled a flat snail, had a muscular leg with the help of which it moved, and a mantle from which the spines on its back grew. Analysis of the remains showed that the spines were not formed due to mineralization of the mollusk's body, but due to the release of chitin, a natural polymer that makes up the external skeletons of arthropods. Since such spines, sclerites, are also characteristic of annelids, paleontologists placed S. aculeata on the evolutionary tree between them and molluscs, but closer to modern molluscs than to another ancient mollusc, Wiwaxia.
