Marella

Marella splendens is an unusual arthropod known only from a single bed in the Middle Cambrian Burgess Shale of British Columbia. It is, however, quite numerous in that bed and is the most common fossil in the Burgess Shale with over 15000 specimens catalogued. Historically, Marella was the first fossil collected by Charles Walcott from the Burgess Shale. Walcott described Marella informally as a "lace crab" and described it more formally as an odd Trilobite. It was later reassigned to the now defunct class Trilobitoidea in the 'Treatise on Invertebrate Paleontology'. In 1971, Whittington did a thorough redescription of the animal concluding on the basis of its legs, gills and the appendages on the head that it was not a trilobite, not a chelicerate ,and not a crustacean.

Marella itself is a small animal 2cm or less in length. The head shield has two pairs of long rearward directed spikes. On the bottom side of the head are two pairs of antennae, one long and sweeping, the second shorter and stouter. The two dozen segments each have a pair of six segmented biramous legs with feathery gills branching off above the leg. There is a tiny, button like telson at the end of the thorax. It is unclear how the unmineralized head and spines were stiffened. Marella has one too many antennae pair, three too few cephalic leg pairs and two to few segments per leg to be a trilobite. It lacks the three pairs of legs behind the mouth that are characteristic of crustacea. The legs are also quite uncrustacean.

The best modern guest is that Marella is a moderately evolved primitive arthropod descended from a common ancestor of the major later arthropod groups. It is thought to have been a bottom dwelling marine scavenger living on detrial and particulate material. It has no known ancestors, descendants or close relatives.