Shishania aculeata lived during the mid-Cambrian, around 512 million years ago, in shallow tropical waters covering what is now southwestern China.
Up to about 6cm in length (~2.4″), its spine-covered body was initially thought to be an early mollusc, but the discovery of more specimens has resulted in a new interpretation: instead of a slug-like creature, the fossils of Shishania might instead represent a flattened and ruptured chancelloriid.
Chancelloriids were an enigmatic group of Cambrian animals that had hollow bag-like bodies armored with numerous sharp star-shaped spines. They were historically classified as sponges due to their similar body plan and immobile filter-feeding lifestyle, and they’ve also been proposed to be relatives of halkieriid molluscs due to similarities in the microscopic structure of their spines – but currently it seems most likely that chancelloriids were actually their own separate lineage of early animals, closer related to eumetazoans than to sponges.
Shishania had much simpler spines than other chancelloriids, so it may represent an early stage of the evolution of these animals’ armor, showing that these structures were developed from scratch rather than adapted from a pre-existing ancestral feature.
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