A species of these organisms that act as pests in one ecosystem are injected with bile salts using autonomous drones like RangerBot. A relaxin-like peptide hormone found in these organisms called “gonad-stimulating substance” makes them a useful model to study oocyte maturation. They aren’t deer, but two recent studies have disproved the theory that the densovirus SSaDV caused a mysterious “wasting disease” in these organisms. The Triton Snail is one of the few natural predators capable of containing outbreaks of a corallivorous type of these animals in the genus Acanthaster. Studying the purple Pisaster genus (-5[1])of these animals in rocky intertidal ecosystems led Robert (10[1])Paine to coin the term “keystone species.” For 10 points, what echinoderms are named for having five arms? ■END■ (10[1])