Still Life with Lobster. Lobsters are a family of large marine crustaceans. Lobsters have long bodies with muscular tails, and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, which are usually much larger than the others. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate. Commercially important species include two species of Homarus from the northern Atlantic Ocean, and scampi-the Northern Hemisphere genus Nephrops and the Southern Hemisphere genus Metanephrops. Although several other groups of crustaceans have the word lobster in their names, the unqualified term lobster generally refers to the clawed lobsters of the family Nephropidae. Clawed lobsters are not closely related to spiny lobsters or slipper lobsters, which have no claws, or to squat lobsters. The closest living relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish. Lobsters are invertebrates with a hard protective exoskeleton. Like most arthropods, lobsters must moult to grow, which leaves them vulnerable. During the moulting process, several species change color. Lobsters have eight walking legs; the front three pairs bear claws, the first of which are larger than the others. The front pincers are also biologically considered legs, so they belong in the order Decapods. Although lobsters are largely bilaterally symmetrical like most other arthropods, some genera possess unequal, specialized claws. Lobster anatomy includes two main body parts: the cephalothorax and the abdomen. The cephalothorax fuses the head and the thorax, both of which are covered by a chitinous carapace. The lobster's head bears antennae, antennules, mandibles, the first and second maxillae. The head also bears the compound eyes. Because lobsters live in murky environments at the bottom of the ocean, they mostly use their antennae as sensors. The lobster eye has a reflective structure above a convex retina. In contrast, most complex eyes use refractive ray concentrators and a concave retina. The lobster's thorax is composed of maxillipeds, appendages that function primarily as mouthparts, and pereiopods, appendages that serve for walking and for gathering food. The abdomen includes pleopods, used for swimming as well as the tail fan, composed of uropods and the telson. Lobsters, like snails and spiders, have blue blood due to the presence of hemocyanin, which contains copper. In contrast, vertebrates and many other animals have red blood from iron-rich hemoglobin. Lobsters possess a green hepatopancreas, called the tomalley by chefs, which functions as the animal's liver and pancreas. Lobsters of the family Nephropidae are similar in overall form to a number of other related groups. They differ from freshwater crayfish in lacking the joint between the last two segments of the thorax, and they differ from the reef lobsters of the family Enoplometopidae in having full claws on the first three pairs of legs, rather than just one. The distinctions from fossil families such as the Chilenophoberidae are based on the pattern of grooves on the carapace. Typically, lobsters are dark colored, either bluish green or greenish brown as to blend in with the ocean floor, but they can be found in a multitude of colors. Lobsters with atypical coloring are extremely rare, accounting for only a few of the millions caught every year, and due to their rarity, they usually aren't eaten, instead released back into the wild or donated to aquariums. Often, in cases of atypical coloring, there is a genetic factor, such as albinism or hermaphroditism. Notably, the New England Aquarium has a collection of such lobsters, called the Lobster Rainbow, on public display. Special coloring doesn't appear to have an effect on the lobster's taste once cooked; with the exception of albinos, all lobsters possess astaxanthin, which is responsible for the bright red color lobsters turn after being cooked.