Non-carnivorous feeding in Arctic chaetognaths

•Diet differences were evident in the gut contents and biochemistry of Arctic arrow worm species.•Nine months of data from the Beaufort Sea showed abundant green detritus and oil droplets in the guts of only E. hamata.•The green detritus contained diatoms with a honeycomb structure (supported by biochemistry).•E. hamata likely receives an energy input from direct diatom ingestion and is thus not a strict carnivore.•Multiple signals suggest that P. elegans has a reduced dependence on diatoms for food.•Our data provide the stimulus for continued focus on non-carnivorous feeding in chaetognaths.