Eunereis longissima (Johnston 1840)

Sexually ripe specimens have been observed in April and May. Most probably the larvae have a planktonic development. E. longissima lives in burrows. When conditions become unfavourable it will rapidly and repeatedly move and set up a new tube at other locations. E. longissima is mainly a non-selective deposit feeder, feeding on algae and dead animals. The species itself is eaten by flatfish (Hartmann-Schröder, 1971; Wolff, 1973; Fauchald & Jumars, 1979).

The bristle worm Eunereis longissima can reach a length of up to 50 cm, although only smaller specimens with a maximum length of 20cm have been found on the Belgian part of the North Sea. The striking head structures with tentacles, palps, antennae and four eyes are characteristic. Living specimens have a red to iridescent dark brown colour.

N. longissima occurs from the subtidal zone of the Wadden Sea and the Delta area down to a depth of 50 m in the Oyster Ground, where it is quite abundant. In the offshore part of the Southern Bight N. longissima is almost absent.

With only eight observations and a maximum density of 16 ind./m2 Eunereis longissima was a rare phenomenon in the entire near-coastal zone in the 1976-1986 period. In the 1994-2001 period the number of observations increased and densities up to 100 ind./m2 were noted. The species still mainly occurred near the coast, but clearly avoided the eastern coastal zone.

Its density distribution suggests a preference for substrates with an admixture of mud.

Eunereis longissima is typically found in sediments with a median grain size of 100 to 250 µm. The species has a broad mud content tolerance but tends to prefer (relative occurrence: > 50%) sediments with a mud content of 10-20%.

A species with a long, rather flattened body of up to 150 mm in length, with over 200 segments. The head is conical, truncate, with two frontal antennae, two biarticulate palps and four relatively small eyes. The first segments bears four pairs of cirri. Like all nereids, the species has an eversible proboscis and two terminal jaws. The small number of teeth on the proboscis are characteristic for this species. The body segments are rather uniform, with prominent, powerful parapodia bearing distinct lamellae. lt is blue-grey, reddish or pinkish in colour (Hartmann-Schröder, 1971; Hayward & Ryland, 1990).