Key: Step 241. Arenicolidae

19 anterior segments bearing chaetae, of which 7-19 bear gills, followed by a narrower posterior region lacking gills and chaetae

Arenicola marina

Arenicola marina

The first 15-16 chaetigers without gills, 30-40 pairs of gills posteriorly. No achaetous tail

Arenicolides ecaudata

Arenicolides ecaudata
Decision path