Just a few ideas:
Disposer - a creature that somehow eliminates garbage & waste
Floater - a creature that lives only on the surface of water, not above or below
Hive Builders - a species that lives and works together in massive communities, like ants or bees do. Maybe disallow entries of insect species to push for more original concepts.
And perhaps as a follow-up to the asymmetrical theme - create a creature with radial (circular) symmetry.