Eunicidae is a family of polychaetes. Many eunicids reach a considerable size. Their jaws are known from Ordovician sediments. They live throughout the seas; a few species are parasitic.
One of the most conspicuous of the eunicids is the giant, dark-purple, iridescent "Bobbit worm" (Eunice aphroditois), found at low tide under boulders on southern Australian shores. Its robust, muscular body can be as long as 2 m.
Some species of eunicids prey on coral. Individuals have been found living unnoticed in reef aquaria for long enough to grow to great size.