Marrella

Marrella was a primitive arthropod from the Middle Cambrian Burgess Shale. It is the most common fossil found in the formation.

Description
Marrella was a small creature, measuring 2 centimeters long at most. Its most prominent feature was its head shield, which had two pairs of rear-facing spikes. Marrella walked on the sea floor using around 50 individual legs, with each leg supporting a feathery gill-like structure. In life, the hard parts of Marrella would have been iridescent.

Classification
At the current time, Marrella is best classified as a stem group arthropod, and not a type of trilobite as its morphology would suggest.

Discovery
Marrella was the first type of fossil collected by Charles Walcott from the Burgess Shale in British Columbia. He described it in 1912, identifying it as a possible trilobite. In 1971, Harry Whittington published a redescription of the animal and concluded that Marrella was not actually a trilobite, nor was it part of any extant arthropod group. It was subsequently labeled as a stem group arthropod.

Since its discovery, over 25,000 specimens of Marrella have been collected, making up a significant portion of the specimens found in the Greater Phyllopod bed.

Paleobiology
Marrella is thought to have been a deep-sea scavenger, living on the ocean floor and feeding on small particles of organic material. One particular specimen shows that the animal molted its shell, rather like living marine invertebrates.