Sidneyia

Sidneyia is an extinct arthropod known from fossils found in the Cambrian-age Burgess Shale formation of British Columbia.

Sidneyia ranged from 2 to 5 inches in length and is one of the largest arthropods found at the site. It was a benthic carnivore that walked along the sea floor in search of prey. Gut contents have revealed Sidneyia dined on hyolithids (molluscs) and other small crustaceans and trilobites.

Sidneyia was discovered during the first day of Charles Walcott's exploration of the Burgess Shale. Walcott's oldest son, Sidney, was the first to discover the fossil, and Walcott named it after him. The species name, Sidneyia inexpectans, means "Sidney's discovery".

About 200 specimens have been documented.