Key to the North East Atlantic species of Terebellides

1. Geniculate acicular chaetae on thoracic chaetiger 6........................................................... 2

- Geniculate acicular chaetae on thoracic chaetigers 5 and 6.................................. T. bigeniculatus sp. nov.

2. Chaetigers 1 to 4 ventrally whitish................................................................. T. gracilis

- Chaetigers 1 to 4 of same coloration as the following......................................................... 3

3. Branchial lobes fused; a large species (body up to 50 mm long)......................................... T. stroemii

- Branchial lobes free; a small species (body less than 20 mm long)........................................ T. atlantis