Eulalia clavigera is a species of polychaete worm in the family Phyllodocidae, native to the coasts around Britain, through Western France, and to the Iberian Peninsula. It closely resembles Eulalia viridis, and there has been confusion in the past as to the identification of the two species.

A long, thin, dorsally flattened worm, between 2.7 and 9.4 cm in length, composed of ca 134 segments. It is a conspicuous worm, deep emerald green in colour, although males are lighter in colour and juveniles are light green.

Eulalia clavigera | (Audouin & Milne Edwards, 1833) N° 215 Mer du Nord, Manche, Atlantique Nord-Est, Méditerranée (rare) Clé d'identification 5 à 15 cm de long, 1 à 3 mm de large, nombreux segments identiques Couleur vert foncé Parapodes étroits et pointus, de couleur vert clair 4 paires de cirres tentaculaires en arrière de la tête