They are typically found on the bottom of shallow marine waters, and some species (e.g. common bloodworms) can grow up to 35 cm (14 in) in length.

[1][2] Bloodworms have a creamy pink color, as their pale skin allows their red body fluids that contain haemoglobin to show through.

The jaws are connected to glands that supply venom which they use to kill their prey, and their bite is painful even to a human[5].

Reproduction occurs in midsummer, when the warmer water temperature and lunar cycle among other factors triggers sexually mature worms to transform into a non-feeding stage called the epitoke.

It contains the following species as of October 2023:[10] Glycera worms are sold commercially in tackle shops as bait for saltwater fishing.