Arrow worms are an important part of plankton biomass in the sea. They are real predators that can detect vibrations in the water with a system similar to the sidelines of fish and strike quickly, after which they grab the prey with hook-shaped bristles on the head. They are very fast swimmers and most will have likely escaped quickly when sampling with a plankton net.
Arrow worms are hermaphroditic, and have both ovaries and testes in their bodies. There is no larval stage, young arrow worms can look for food almost immediately.