Body of uniform width, tapering posteriorly. Prostomium rounded. Median antenna shorter than paired ones, situated slightly in front of eyes. Eyes on posterior part of prostomium, rather small, rounded. Proboscis diffusely covered with conical papillae. Tentacular cirri of segment 1 slightly shorter than segment width. Dorsal tentacular cirri of segments 2 and 3 reaching about segment 5. Ventral tentacular cirri of segment 2 short and flattened, with about five chaetae arising from the anterior part of the cirrophores. Dorsal cirri of median segments slightly flattened, ovoid. Parapodial lobes rounded, with about 6-8 compound chaetae. Terminal end of chaetal shaft with a large number of teeth, slightly decreasing in size proximally. Blades rather broad. Ventral cirri smaller and more pointed than dorsal ones. Pygidial cirri slightly flattened, about 1.5 times as long as broad. Small median pygidial papilla present. Single bands of cilia ventrally on each segment (E. expusilla-detail).
Up to 16 mm for 80 segments.
Living animals yellowish with a dark greenish-black mid-dorsal longitudinal line, present from segment 1. Less distinct pigmentation present laterally, on the dorsal sides of parapodia. Ventral dark spots occur near parapodial bases on some specimens. Eyes clear red. Preserved animals vary in colour from yellowish to dark brown. Dorsal cirri often dark. Median line usually retained. Eyes brownish.
On rocky substrata, among kelp holdfasts and coarse shell gravel. Known to 280 m.
Western Mediterranean, western North Sea, English Channel.