Marrella

The marrella is a segmented arthropod with the low, plated shape of a trilobite and the busy legs of a centipede. Its most striking feature is a pair of long, fluffy-looking antennae. These are not feelers at all but gills, which is why the creature lives mostly in water.

Each of the two whiplike antennae can lash an enemy for 1d6 points of damage. A marrella with at least 10 feet of room between itself and a target can instead charge, slamming its heavily plated head into the foe for 2d8 points of damage. That head is the toughest part of the animal, so blows aimed at it accomplish less than strikes against the softer body.

Although it breathes through its antenna-gills, a marrella can survive out of the water for up to an hour at a stretch. It often uses that window to scuttle overland from one pond, stream or lake to the next, so travelers sometimes meet one far from any shoreline.