O. Schmidt, 1848
Prostomium separated from the trunk by a transverse furrow; with 3 multiannulated antennae (max. length 700 µm) in anterior part. Median antenna usually the longest, slightly dorsoposterior to lateral antennae. All antennae with oblong bead-like joints, the numbers of which vary (lateral antennae 6-9, median antenna 4-8); joints of individuals from the French Atlantic coast may be more slender and less constricted than those of worms from more northern waters. Two laterally positioned club-shaped palps. Four eyes with lenses and a conspicuous silvery appearance. Two nuchal organs in the form of a deep crescentic groove dorsolaterally on each side of the posterior part of the prostomium, communicating with the mouth region by a deep groove. Nine chaetigers, posterior ones the shortest. Buccal segment distinctly different, with one pair of 4-6 jointed peristomial cirri about twice as long as cirri of following segment. One bundle of 2-9 chaetae emerging dorsally from the base of the cirri. Following 7 segments each with one pair of simple elongate cirri (up to 130 µm long in North Sea specimens). Last segment (chaetiger 9) without cirri. Parapodia in segments 2-8 each with a dorsal and ventral bundle of 8-16 serrate capillary chaetae (N. antennata-parapodium). Cirri of these segments much shorter than chaetae. Dorsum of segments 2-9 with transverse ring of cilia behind each pair of parapodia. Dorsum of the buccal segment with lateral ciliary tufts on each side. Each segment also with lateral patches of cilia. Pygidial cirri up to 900 µm long with 3-7 joints. Buccal pieces present but hard to recognize by light microscopy.
Length 1.5-1.7 mm.
Transparent; intestine often conspicuously dark green or greenish brown.
Interstitial in a wide range of substrata: silt and mud as well as sand with gravel; in intertidal and subtidal areas, with preference for coarse sand-gravel habitats. Also on benthic algae.
North Atlantic, North Sea, English Channel, Irish Sea, Swedish west coast, Baltic, Mediterranean, Black Sea, South West and South Africa, Atlantic (Massachusetts) and Pacific coasts (Washington) of North America, India.