Abstract
Ophiodromus flexuosus is an important faunal element of the polluted Oslofjord, but its life history was previously unknown. A complete series of developmental stages is illustrated and described based on wild-caught planktonic and benthic larvae and larvae reared in the laboratory. Ophiodromus flexuosus carries 20 000 eggs (Ø= 108 µm) and spawns in autumn. Larval development is planktotrophic for 1–2 months. The benthic larva grows c. 1 segment per month and increases from c. 0.5 mm (young bottom living larva) to 2–3 mm (juvenile) in the first year. A further year of growth elapses before spawning takes place. After spawning the adult starts to produce new genital products. The larvae can be separated from other hesionids by their red eyes and lack of ventral cirri on the second and third segments. They have fewer segments in relation to their length than other hesionid larvae from Oslofjorden. The presence of only 1–2 capillary setae without spines on each segment separates Ophiodromus flexuosus larvae from Gyptis rosea larvae.
