Body relatively short and broad, up to 34 segments and a 'tail', which missing in young individuals. Without obvious segmentation other than elongated parapodia.
Prostomium with 2 short, divergent antennae, two eyes with lenses and two ciliated nuchal organs. Length of cirriform appendages of the second segment at least half the body length.
14-21 parapodia and a 'tail' bearing 10-14 very reduced parapodia. Tail may be a third of the total body length. All parapodia with rosette organs in the tips of both branches; yellow in life, brownish in preserved specimens (T. helgolandica-detail).
Parapodia without chaetae.
Commonly 20-40 mm in length including the tail.
Body striated with dark brown lines in life, but transparent when fixed..
Pelagic, usually near the coast.
Arctic, Atlantic, Mediterranean, English Channel, North Sea, Skagerrak, Kattegat, Öresund to Bay of Kiel.