Cyclidans were an enigmatic group of crustaceans that first appeared in the Early Carboniferous (~358 million years ago) and survived all the way until the Late Cretaceous (~66 million years ago). They had body plans resembling crabs — making them an example of carcinization — with flattened round carapaces and pincer-like front appendages.
Their exact evolutionary relationships within Crustacea have been debated for a long time, but recent studies suggest they may have been most closely related to both malacostracans and the also-mysterious thylacocephalans.
Chernyshevine spinosus was an Early Carboniferous cyclidan, living about 340 million years ago in what is now Tajikistan in Central Asia. Around 2cm long (~0.8″), it had a rather domed carapace covered in small bumps — and also long pointed spines around its edges, a feature not seen in any other known cyclidan.
It inhabited shallow marine waters and probably had a similar lifestyle to the crabs it resembled, scuttling around in reefs and feeding omnivorously using its claws to manipulate food items.
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