Marrella has too many antennae, too few cephalic legs, and too 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 different from those of crustaceans, with the first pair modified into a single pair of pleopods with a copious blood supply.[4] The identification of a diffraction grating pattern on well-preserved Marrella specimens proves that it would have harboured an iridescent sheen—and thus would have appeared colourful.[5] Dark stains are often present at the posterior regions of specimens, probably representing extruded waste matter[6] or hemolymph.[7]