O.F. Müller, 1776
Body narrow, tapering posteriorly.
Prostomium with a pair of short antennae without cirrophores, a pair of biarticulate palps extending beyond the antennae and two pairs of eyes in a trapezoidal arrangement (N. diversicolor-head).
Dorsal tentacular cirri longer than ventral ones, second dorsal tentacular cirrus reaching to chaetiger 3.
Pharynx with a pair of denticulate jaws; oral and maxillary rings with conical paragnaths; group I: 1-3 (0-5), groups II, III and IV: numerous; group V: absent; group VI: 3-5 (3-9); groups VII-VIII: irregular rows (N. diversicolor-proboscis).
Parapodia of the first two chaetigers uniramous with 3 lobes. Remaining parapodia biramous, with 4 lobes. Lobes all relatively short, dorsal notopodial lobe wide in anterior chaetigers becoming narrower posteriorly; notopodial acicular lobe bilobed, with a small but distinct supra-acicular lobe on all parapodia; neuropodial acicular lobe with a prominent postchaetal lobe only in the anterior chaetigers, absent from approximately chaetiger 30; ventral neuropodial lobe short. Dorsal and ventral cirri much shorter than the parapodial lobes.
Notopodial chaetae all homogomph spinigers.
Neuropodial chaetae homogomph spinigers with occasional heterogomph falcigers above the acicula, heterogomph spinigers and falcigers below it. In posterior chaetigers (approximately from chaetiger 40 in large animals) single stout simple acicular chaetae (fused falcigers) replace heterogomph falcigers above the acicula in neuropodia (N. diversicolor-detail).
Up to 200 mm for 120 chaetigers.
In living animals very variable: yellowish, greenish, orange or reddish brown with two dark, longitudinal bands.
No external signs of epitoky are visible, although internal changes to the gut and musculature do occur in mature animals.
A characteristic inhabitant of estuaries, in both low and fluctuating salinities. Also sometimes found on apparently fully marine beaches, where it inhabits local areas with reduced salinity.
Northeast and Northwest Atlantic, Mediterranean, Black and Caspian Seas.