#notatrilobitebutclose

[mineralsrocksandfossiltalks]

Fossil Friday: Marella splendens

This weird looking animal is called Marella splendens. It comes from the middle Cambrian Burgess Shale of British Columbia (and to much, much lesser extent, the Chengjiang Biota of China). Discovered by Charles Walcott, he informally called it a lace crab. In fact, this was the very first fossil he collected in 1909 when he found the Burgess Shale deposits. Walcott thought it was some sort of very odd looking trilobite.

In 1971, Harry Whittington decided to thoroughly redescribe it and came to the conclusion it was not a trilobite not a chelicerate (group that includes arachnids and horseshoe crabs) nor a crustacean. He did this on the basis of its legs, gills, and head appendages. While it may not be in any of those groups, it is an arthropod.

Marella is a very small animal ranging from a little over 2mm to nearly 25 mm (less than an inch in length). The four projections on its head make it look a bit like the top of a pitchfork which I imagine made it very hard to predate on.

There were many other interesting features of the head besides the crazy headgear. This animal apparently had no eyes which would explain the need for long antennae broken into as much as 30 segments. That's not even the weirdest part! Marella's stomach was located in the head right behind the mouth! Talk about using your stomach to think.

Marella was an active, nektobenthic swimmer that moved around just above the sea floor. It could rest on the sea floor by standing on its body appendages. It was a deposit feeder, meaning it ingested sediment to consume organic matter. The net of internal projections on the last twelve body segments would have been used to trap food particles located in water currents and to pass them along the underside of the animal. Food particles trapped in the net would be moved towards the mouth using the tips of the anterior legs.

Marella is one of the most common fossils found in the Burgess Shale. Over 25,000 specimens have been recovered and it is the second most common arthropod after trilobites. That's a lot of sea bugs.