Marella splendens was an arthropod that occupied the Mid-Cambrian and is found in the Burgess Shale formation, and is the most common animal found in said formation. It was once thought to be a trilobite of sorts, but this has since been corrected. It has, since being described as a trilobite, been found to be another type of arthropod all together, and has gained it’s own distinction among them.
M. splendens grew to about two centimeters, had 24 to 26 segments, each with a pair of branched legs; the branches being gills located on the upper portion of each leg, with the lower portion being used for walking. It had two pairs of antennae, one pair being long and sweeping and the other pair being short and stout. It’s head also had two pairs of rearward facing, for lack of a better term, spikes. It had too few segments per leg to be a trilobite, not to mention too many antennae. It also couldn’t be a crustacean as it lacked the three pairs of legs located behind the mouth. Studies show that it had an iridescent sheen and would have appeared colorful.
By Wilson44691 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons