Lobster
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| Nephropidae | |||||||||||||
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| American lobster, Homarus americanus | |||||||||||||
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Lobsters are large crustaceans that live in the sea. They form the family of Nephorpidae, which is sometimes also called Homaridae. Lobsters are an economically important type of seafood.
[change] Biology
Several different groups of crustaceans are known as lobsters. When people talk about lobsters, they mean clawed lobsters most of the time, such as the genus Homarus. Clawed lobsters are not closely related to spiny lobsters or slipper lobsters, which have no claws (chelae), or squat lobsters. The closest relatives of clawed lobsters are the reef lobster Enoplometopus and the three groups of freshwater crayfish.
Smaller kinds are sometimes called "lobsterettes". Lobsters are invertebrates, and have a hard exoskeleton (outer skeleton), which protects them. Like most arthropods, lobsters must shed it in order to grow. This is called moulting. It makes them weak and easy to attack during this time. When they are moulting, some species' colors might change.
Lobsters live on rocky, sandy, or muddy bottoms from the shore to beyond the edge of the continental shelf. They usually live alone in cracks or in burrows under rocks.
Lobsters usually eat live food, consisting of fish, mollusks, other crustaceans, worms, and some plant life. Sometimes, they will scavenge (eat dead plants and animals) if necessary, and may eat each other (cannabalism) when they are in captivity; however, this has not been observed in the wild. Lobster skin in the stomachs of lobsters has been found before, although this is because lobsters will eat their shed skin after molting [1]. Lobsters grow throughout their lives and it is not unusual for a lobster to live for more than 100 years [2]. They can thus reach impressive sizes. According to the Guinness World Records, the largest lobster was caught in Nova Scotia, Canada and weighed 20.14 kg (44.4 lb).
Being arthropods, lobsters are largely bilaterally symmetrical (they are the same on the left and right sides). Clawed lobsters often have unequal, specialized claws, like the king crab. A freshly caught lobster will have a claw that is full and fleshy, not small. Lobsters have the cephalothorax which is the head connected to the thorax, both of which are covered by the carapace, of chitinous composition, and the abdomen. The lobster's head has two pairs of antennae, three pairs of jaws. Because a lobster lives in a murky environment at the bottom of the ocean, its eyesight is poor and it mostly uses its antennae to feel around. Studies have shown that the lobster eye is formed with a reflective structure at the top a rounded retina (eye part). In contrast, most complex eyes use lenses that change the direction of rays and a inward-curving retina [3]. The abdomen of the lobster includes swimming legs and a tail fan.
In general, lobsters move slowly by walking on the bottom of the sea floor. However, when they are in danger and need to escape, they swim backwards quickly by curling and uncurling their abdomen. A speed of 5 metres per second has been recorded.
[change] References
- ↑ "Homarus americanus, Atlantic lobster". http://marinebio.org/species.asp?id=533. Retrieved December 27, 2006.
- ↑ David Foster Wallace (2005). Consider the Lobster and Other Essays. Little, Brown & Company. ISBN 0-31-615611-6.
- ↑ Land, M. F. (1976). "Superposition images are formed by reflection in the eyes of some oceanic decapod Crustacea". Nature 263: 764-765.
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