The genus Glycera is a group of polychaetes (bristle worms) commonly known as blood worms. They are typically found on the bottom of shallow marine waters, and some species (e.g. the proboscis worm, Glycera dibranchiata), are extensively harvested for use as bait in fishing. Another common species is the tufted gilled bloodworm, G. americana.
Bloodworms are carnivorous. They feed by extending a large proboscis that bears four hollow jaws. The jaws are connected to glands that supply poison which they use to kill their prey, and their bite is painful even to a human. They are preyed on by other worms, by bottom-feeding fish and crustaceans, and by gulls.
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. With enlarged parapodia, they swim to the surface of the water where both sexes release gametes, and then die.
The animals are unique in that they contain a lot of copper without being poisoned. Their jaws are unusually strong since they too contain the metal in the form of a copper-based chloride biomineral, known as atacamite. And unlike the clamworm (Nereis limbata), whose jaws contain the metal zinc, the copper in the mineral in the jaws of Glycera is actually present in its crystalline form. It is theorized that this copper is used as a catalyst for its poisonous bite.