haemerythrins

thumb|right|Trimeric Hemerythrin Protein Complex () Hemerythrin (also spelled haemerythrin; , ) is an oligomeric protein responsible for oxygen (O2) transport in the marine invertebrate phyla of priapulids, brachiopods, and in the annelid worm clades Magelona and Sipuncula. Myohemerythrin is a monomeric O2-binding protein found in the muscles of marine invertebrates. Hemerythrin and myohemerythrin are essentially colorless when deoxygenated, but turn a violet-pink in the oxygenated state.

Hemerythrin does not, as the name might suggest, contain a heme. The names of the blood oxygen transporters hemoglobin, hemocyanin, and hemerythrin do not refer to the heme group (only found in globins). Instead, these names are derived from the Greek word for blood. Hemerythrin may also contribute to innate immunity and anterior tissue regeneration in certain worms.