It can range from 5 to 15 cm (2 to 6 in) in length and is usually found in shallow north Atlantic water under rocks or in mussel beds.

The head bears five antennae, two eyes and four pairs of tentacular cirri; the eversible proboscis is cylindrical and dotted with rounded papillae.

[5] Before the 1990s, E. viridis was thought to have a wide range in the northeastern Atlantic including the waters around the United Kingdom, but morphological and biochemical studies led to the southern populations being recognised as a separate species Eulalia clavigera, part of a species complex with E.

It is typically found on rocky coasts and on shelly gravel,[7] in rock crevices and mussel beds.

[5] Although many worms in this family are predators and actively hunt prey, E. viridis seems to be more selective in its diet, and researchers found that it only consumed moribund or dead animal tissue.