Heteromastus sp. (Eisig, 1887)
Up to 180 mm long and maximal 1 mm wide, for more than 150 segments.
Anterior body red; posterior body yellowish or reddish-green.
Lives in branching burrows, supported by mucus. Produces wormcasts on the surface of the bottom. From upper eulittoral down to lower abyssal (4680 m). Favours muddy sand and tolerates pollution and changing salinity grades.
Burrowing head-down feeders.
Free spawning with planktotrophic larvae.
Arctic, North Pacific, North Atlantic.