Lobster

**Lobsters** comprise a family (**Nephropidae**, sometimes also **Homaridae**) of large marine crustaceans. 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 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 (chelae), or to squat lobsters. The closest living relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish.

## Description

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 10 walking legs; the front three pairs bear claws, the first of which are larger than the others. Although lobsters are largely bilaterally symmetrical like most other arthropods, some genera possess unequal, specialised claws.

Lobster anatomy includes the cephalothorax which fuses the head and the thorax, both of which are covered by a chitinous carapace, and the abdomen. The lobster's head bears antennae, antennules, mandibles, the first and second maxillae, and the first, second, and third maxillipeds. 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 abdomen includes swimmerets and its tail is 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.

## Longevity

Lobsters live up to an estimated 70 years, although determining age is difficult. In 2012, a report was published describing how growth bands in calcified regions of the eyestalk or gastric mill in shrimps, crabs, and lobsters could be used to measure growth and mortality in decapod crustaceans. Without such a technique, a lobster's age is estimated by size and other variables; this new knowledge "could help scientists better understand the population and assist regulators of the lucrative industry".

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, referred to as 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. Lobsters, like many other decapod crustaceans, grow throughout life, and are able to add new muscle cells at each molt. 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).

## Ecology

Lobsters are found in all oceans. They live on rocky, sandy, or muddy bottoms from the shoreline to beyond the edge of the continental shelf. They generally live singly in crevices or in burrows under rocks. Lobsters are omnivores and typically eat live prey such as fish, mollusks, other crustaceans, worms, and some plant life. They scavenge if necessary, and are known to resort to cannibalism in captivity. However, when lobster skin is found in lobster stomachs, this is not necessarily evidence of cannibalism – lobsters eat their shed skin after moulting. While cannibalism was thought to be nonexistent among wild lobster populations, it was observed in 2012 by researchers studying wild lobsters in Maine. These first known instances of lobster cannibalism in the wild are theorized to be attributed to a local population explosion among lobsters caused by the disappearance of many of the Maine lobsters' natural predators.

In general, lobsters are 25–50 cm (10–20 in) long, and move by slowly walking on the sea floor. However, when they flee, they swim backward quickly by curling and uncurling their abdomens. A speed of 5 m/s (11 mph) has been recorded. This is known as the caridoid escape reaction. Symbiotic animals of the genus *Symbion*, the only member of the phylum Cycliophora, live exclusively on lobster gills and mouthparts. Different species of *Symbion* have been found on the three commercially important lobsters of the North Atlantic Ocean – *Nephrops norvegicus*, *Homarus gammarus*, and *Homarus americanus*.

## As Food

Lobster recipes include lobster Newberg and lobster Thermidor. Lobster is used in soup, bisque, lobster rolls, and *cappon magro*. Lobster meat may be dipped in clarified butter, resulting in a heightened flavor. Cooks boil or steam live lobsters. When a lobster is cooked, its shell's colour changes from blue to orange because the heat from cooking breaks down a protein called crustacyanin, which suppresses the orange hue of the chemical astaxanthin, which is also found in the shell. According to the United States Food and Drug Administration (FDA), the mean level of mercury in American lobster between 2005 and 2007 was 0.107 ppm.