A new genus and species of an endobenthic, unusually large eumonostiliferous hoplonemertean, Arenogigas armoricus gen. et sp. nov., is described from an intertidal sandflat in Pouldohan Bay near Concarneau, France. Morphological characters of the species and genus include a prominent connective tissue that divides the anterior longitudinal musculature, an extremely branched vascu- lar system, the absence of a pre-cerebral septum, a pair of eyes situated at the anterior tip of the head, small cerebral organs positioned far anterior to the brain, 10 proboscidial nerves, and nine accessory stylet pouches.