Lobsters are malacostracan decapod crustaceans of the family Nephropidae or its synonym Homaridae. They 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 the coastal areas they populate. Commercially important species include two species of Homarus from the northern Atlantic Ocean; the smaller Nephrops norvegicus, known as true scampi, Norway lobster, or langoustine; and multiple small species in the genus Metanephrops, commonly called Pacific scampi.
Distinction 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 langustas (spinys and slipper lobsters), which have no claws (chelae), or to squat lobsters. The most similar living relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish. In the United States, the only species whose Acceptable Market Names are "lobster" with no qualification are the Homarus species: H. gammarus (European Lobster) and H. americanus (American lobster). In culinary contexts, the unqualified term "lobster" almost always means the American lobster in North America and the European lobster in Great Britain. Qualified names are used for other species, whether they are clawed lobsters in the Nephropidae family (like Norway lobster, Nephrops norvegicus) or not (like spiny lobster). In the Caribbean, Panulirus argus is formally called the spiny lobster, but informally simply "lobster". In other English-speaking areas, the unqualified term "lobster" is rarely used.
Description
Body
Lobsters are invertebrates with a hard protective exoskeleton. Like most arthropods, lobsters must shed to grow, which leaves them vulnerable. During the shedding 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 ("ten-footed"). 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 (usually stalked) 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 (lenses) 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 (also known as swimmerets), 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 in culinary usage, which functions as the animal's liver and pancreas. Lobsters of the family Nephropidae are similar in overall form to several 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. Analysis of the neural gene complement revealed extraordinary development of the chemosensory machinery, including a profound diversification of ligand-gated ion channels and secretory molecules.
Longevity Lobsters live up to an estimated 45 to 50 years in the wild, although determining age is difficult: it is typically estimated from size and other variables. Newer techniques may lead to more accurate age estimates. Research suggests that lobsters may not slow down, weaken, or lose fertility with age and that older lobsters may be more fertile than younger lobsters. This longevity may be due to telomerase, an enzyme that repairs long repetitive sections of DNA sequences at the ends of chromosomes, the telomeres. Telomerase is expressed by most vertebrates during embryonic stages but is generally absent from adult stages of life. However, unlike most vertebrates, lobsters express telomerase as adults through most tissue, which has been suggested to be related to their longevity. Lobster longevity is limited by their size. Moulting requires metabolic energy, and the larger the lobster, the more energy is needed; 10 to 15% of lobsters die of exhaustion during moulting, while in older lobsters, moulting ceases and the exoskeleton degrades or collapses entirely, leading to death. Like many decapod crustaceans, lobsters grow throughout life and can add new muscle cells at each moult. Lobster longevity allows them to reach impressive sizes. According to Guinness World Records, the largest lobster ever caught was in Nova Scotia, Canada, weighing 20.15 kilograms (44.4 lb).
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