Fossil enthusiasts know all about these guys. Brachiopods are ocean-dwelling animals that superficially resemble clams. They've got two articulated shells — or "valves" — apiece: One rests underneath the animal while the other covers it from above. Found in an assortment of marine habitats, the creatures filter tiny food particles out of the water. Although there are over 300 living species, most people associate brachiopods with prehistoric times because the hard-shelled creatures are disproportionately well-represented in much of the fossil record.
Extant brachiopods do not rely on hemoglobin or hemocyanin to ferry oxygen in the blood. That task is left to hemerythrin, yet another pigmented protein. Like hemoglobin, it contains iron atoms, albeit in a different arrangement. Hemerythrin makes deoxygenated blood look either colorless or faintly yellow. However, once the blood starts taking on oxygen, it adopts a violet-to-pinkish hue.
You'll also see this kind of blood in Sipuncula marine worms. Nicknamed "peanut worms" due to their segmented appearance, the creepy crawlies reside in sand, mud, crevices and unoccupied shells among other places.
Other ocean-going worms have a different circulatory setup. If a diver were to spot a live polychaete cruising through the waves, he or she might mistake it for a sentient feather-duster. Most of these worms are covered in bristles and tentacles whose function varies from species to species. Some have red blood, but others harbor green blood. The latter use the oxygen-binding protein chlorochurion in place of hemoglobin. When concentrated, the stuff appears to be green. Those New Guinea skinks have apparently got some company...