Marrella was a small bottom-dwelling ("benthic") animal, about ¾ inch (2 centimeters) or less in length. It had a body consisting of 24 to 26 segments each with a pair of appendages - the appendages each have two branches, a lower branch for walking, and a upper branch with a feathery gill. The animal also a head with two long backward pointing spikes, and eyes beneath the head.
There has been some debate about how Marrella should be classified. The first fossil was described by its discoverer, Charles Walcott, informally as a "lace crab", and more formally as a odd Trilobite. However, while it seems clear that Marrella is a member of the Arthropod phylum (the group containing insects, crustaceans, millipedes, etc.), it does not easily fit into any of the major subdivisions, Marrella has major differences (too many antennae, too few segments per leg, and too few legs) to be a Trilobite, and does not seem to be a Crustacean (a member of the group containing crabs, lobsters, shrimp, etc.), and nor does it seem to be a Chelicerate (a member of the group containing scorpions, spiders, horseshoe crabs, etc.). Today, the general thinking is that Marrella must be a stem group Arthropod - that is to say that it is descended from an ancestor of most/all other Arthropod groups.
Marrella marine animal that lived during the Cambrian period
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