To the bottom is the turtle.

The turtles are Archaean creatures. Their thick shell covered with spikes protects their skeletal bodies. They typically ignore lesser creatures such as Trilobites, but when encountering a creature they consider a threat they retract into their shells and eject a volley of deadly spikes. Both their spikes and themselves deal a third of a bar of damage. The spikes damage Rusty, other enemies (and the Turtle that shot the spikes, assuming the spikes don't go far enough away), and tiles.