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“And two penises. They’re called claspers,” Fred added, raising his eyebrows.

Claspers can be found in shrimp, aquatic insects and even sharks—and, crucially, trilobites’ modern analogues, horseshoe crabs.

Claspers suggest that, in some species, male and female trilobites had different looking bodies.

The looks of claspers in horseshoe crabs helped Losso and her team verify that the Olenoides appendages were more than just malformed feet.

Among them, researchers found two sets of short, grasping appendages that looked an awful lot like reproductive structures called claspers.