Sanctacaris

An illustration of an extinct marine invertebrate. It has a space vaguely like a woodlouse, with an armored segemented body, but instead of legs it has rows of swimming flaps alongs its sides and a lobster-like tail. It has two small widely-set eyes at the front of its shield-like head, along with a pair of long antennae and a pair of shorter spiky appendages. On the undersid eof its head, in front of its mouth, there are two bunches of five segmented spiny mouthparts.

Nicknamed “Santa Claws”, Sanctacaris uncata was a marine arthropod from the Middle Cambrian (~505 mya) Burgess Shale deposits of Canada. Its exact evolutionary relationships are unclear, but it’s thought to have been very closely related to or part of an early branch of the chelicerates – the lineage that includes modern arachnids and horseshoe crabs.

Measuring up to about 9cm long (3.5″), it had forward-facing eyes and five pairs of grasping appendages on the underside of its head, adaptations that suggest it was an active predator convergently similar to anomalocaridids. It probably swam around grabbing onto whatever small prey items it could catch, trapping them in its “limb basket” while it ate them.

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