Introduction to Lobster
Lobster, sea-dwelling animal related to the crayfish, shrimp, and crab. Lobster meat is considered a delicacy. Lobsters are caught in both Atlantic and Pacific waters. They are often marketed alive, but their meat is also available frozen or canned. There are several kinds of lobsters; the most important commercially are the American lobster and various species of spiny lobsters. (Spiny lobsters are also known as rock lobsters and marine crayfish.)Lobsteres have five pairs of legs, including the large claws.
Most of the American lobster catch is made in coastal waters off New England, Nova Scotia, and Newfoundland by using traps made of wood slats and baited with fish. Spiny lobsters are caught in both Atlantic and Pacific waters, primarily with baited wood or wire traps, or with nets.
Lobsters and other crustaceans inhabit all the world’s major oceans. Although lobsters can be found worldwide, different types of lobster choose different areas in which to live. Many lobsters live in shallow water in the coastal areas around islands. One group of lobsters, called deep-sea lobsters, lives in the cold, deep sea.
American lobsters thrive in the cool waters of the North Atlantic Ocean. These lobsters inhabit sandy, muddy, and rocky areas of the ocean floor from Virginia in the United States to Newfoundland and Labrador in Canada. Spiny and slipper lobsters are found in warm waters throughout the world. Spiny lobsters live in coral reefs, on rock ledges, and in crevices. Slipper lobsters are usually found in muddy or sandy places.
A typical American lobster is 12 inches (30 cm) long and weighs about 2 pounds (0.9 kg). Some grow to more than 3 feet (90 cm) long and weigh more than 40 pounds (18 kg). Spiny lobsters are about the same size as American lobsters. Lobsters can live as long as 100 years.Lobster have the same major internal body structures as humans
Lobsters belong to a group of animals called crustaceans. Like other crustaceans, lobsters have a rigid structure called a carapace, or shell, that encloses the soft parts of the body. The carapace may be any of various colors, usually mottled with numerous markings. It is usually dark green in American lobsters and brownish in spiny lobsters. Spiny lobsters have numerous spiny projections on their shells. Lobster shells turn red after they have been cooked.
In days of old, knights wore suits of armor to protect themselves in battle. Lobsters have a natural protective shell of their own, made of a material called chitin (KY tihn).
Like a suit of armor, a lobster’s exoskeleton is made of not one, but many, solid pieces. Some of the pieces are permanently attached to one another and do not move. Others are connected by a flexible material, which lets a lobster move freely.
The exoskeleton of an American lobster is made of 21 different pieces. The head has 6 pieces, the thorax (middle part) 8 pieces, and the tail, 7 pieces. The thickest part of a lobster’s shell—on its back—is called the carapace (KAR uh pays). You can think of it as a shield.
Because lobsters are invertebrates, their shell is their body’s only structural support. A lobster’s muscles are attached to its outer skeleton (shell) as ours are to our internal skeleton. Without its shell, a lobster could not move.
An unjointed shell covers the head and forepart of the body. In the head region the lobster has a pair of compound eyes at the ends of jointed movable stalks, and two pairs of sensory antennae (feelers). Five pairs of legs grow under the forepart of the body. In the American lobster, the first pair has evolved into large, pincer-like claws used to crush prey.
The abdomen is covered by six overlapping shell rings that are joined together. A pair of fringed paddles, called swimmerets, is attached to each of the first five rings. A fan-shaped tail is attached to the last ring. In common usage, the entire abdomen is called lobster tail. Usually this is the only part of a spiny lobster that is eaten. In American lobsters, there is considerable meat in the enlarged claws as well as in the tail.
Lobsters look like they might be hollow, but that is not the case.
Lobsters have the same major internal body structures as humans. Lobsters have a heart that pumps blood around its body and a brain that connects to a nervous system. For eating, digesting, and eliminating food, the lobster has a mouth, stomach, intestines, and anus. Lobsters also have sex organs for reproducing.
While lobsters share similarities with vertebrates, they are much more similar in structure to other invertebrates, especially insects. Like insects, lobsters have an open circulatory system. Animals with such a system lack blood vessels in some areas of their bodies. Blood flows directly into these areas and delivers oxygen and nutrients to the organs and tissues.
If you see an animal walking on the sea floor, and it has a jointed tail, two long antennae, two short antennae, lots of legs, and dark eyes that are on stalks, it is likely to be a lobster.
You can count the number of segments in its tail. A lobster’s tail is made of seven distinct pieces, including the fanlike tip.
Another way to identify a lobster is by the number of its legs. Lobsters have five pairs of legs. Clawed lobsters, such as the American lobster, have front legs that end in large claws. The next two sets of legs have smaller pincers on their tips. Both clawed and clawless lobsters have delicate, leglike limbs under their abdomen that are used for swimming. These limbs are called swimmerets.
Lobsters are known as decapods. “Deca” is a Greek word that means 10, and “pod” is a Greek word that means foot. In addition to the lobster, other 10-footed crustaceans include shrimp and crayfish.
The female American lobster carries fertilized eggs on the underside of its abdomen until the eggs are ready to hatch. The eggs are covered by a sticky cement that hardens and holds them in place. Eggs of the spiny lobster are released to float in the ocean shortly after they have been fertilized. The newly hatched lobsters do not resemble the adults for several weeks, during which time they go through various stages of development.
The lobster molts, or sheds its shell, frequently while young, less frequently as it grows. After molting it is helpless against predators and must hide until the new shell hardens. If it loses a claw or a leg, the lobster grows a new one. Lobsters mature at four or five years of age. Females, depending on their size, produce 3,000 to 100,000 eggs at one time.
It is hard for lobsters to grow. A lobster is, in a sense, trapped in its exoskeleton, because its shell cannot grow larger. For its body to grow larger, a lobster must discard its shell and replace it with a bigger one. This process is called molting.
Before a lobster molts, it forms a new, soft exoskeleton underneath its existing shell. When the lobster is ready to molt, it seeks out a protected place; it is vulnerable to attack until its new shell hardens.
To molt, the lobster shrinks the muscles and other tissues in its limbs by releasing fluid out of the tissues. This lets the lobster withdraw its appendages from the surrounding shell. Once the shell cracks, the lobster is able to withdraw its entire body from its old shell.
After it is out of its shell, the lobster takes in water to swell its body to a larger size. The new soft shell can withstand the pressure from the lobster’s swollen body without cracking. It takes several weeks for the new shell to harden around the swollen lobster. Once the new shell is hard, the lobster pushes the excess water out from its body. It now has a new, roomier shell to grow into.
On its antennae, legs, carapace, and tail, a lobster has tiny, hairlike receptors that can detect specific chemical molecules in the environment, which help the lobster to identify and locate food. The lobster crawls over the bottom of the sea, eating dead and living fish, starfish, clams, and other animals and seaweed. It grinds its food with six pairs of jaws. The food is then further ground and mixed with digestive juices in the stomach, which contains toothlike grinding organs.
A lobster does not smell with a nose, taste with a tongue, or hear with ears. Instead, the animal has special sense organs for collecting information about its marine environment.
Much of the information a lobster gets about its surroundings is gathered by millions of tiny hairlike sensors on its antennae, mouthparts, legs, and shell. Some of these sensors “sniff” chemicals that help lobsters locate and taste food.
Others warn lobsters of predators or alert them to potential mates.A lobster also has special organs located at the base of its antennules, as the shorter pair of antennae are called. These organs are pits that are lined with tiny bristles. As a lobster moves, particles that are floating within the pits bend the tiny bristles in different directions. Signals that are sent from these bristles through the lobster’s nervous system help the lobster determine its position in its surroundings and keep its balance.
In autumn some species of spiny lobsters take part in mass migrations in search of food and warmer waters for mating. As many as 100,000 individuals move south, by both day and night, in single files of about 60 individuals each. They cover about 10 miles (16 km) a day.
To protect themselves from predators, fish swim in schools. Birds fly in flocks. And lobsters “march.” Predators often have a difficult time capturing prey traveling in such groups.
During a lobster march, dozens of spiny lobsters walk together in long rows, like ants or soldiers. The lobsters walk so close together that the antennae of one lobster may touch the tail of the lobster in front of it.
In the Caribbean Sea, lobster marches are often observed after a storm. At these times, the lobsters are usually marching out to deeper water. Some people believe that storms trigger lobster marches. Scientists, however, are not sure why spiny lobsters march to other locations. Are they moving to deeper waters to protect themselves from winter storms? Are they looking for new breeding grounds? New feeding grounds? The answer remains a mystery.
Some lobsters cannot see at all. Deep-sea lobsters, which live in deep and dark places in the ocean, are completely blind. Other lobsters, however, have two working eyes that sit on top of short, movable stalks. Under a microscope, you can see that a lobster’s eyes have anywhere from dozens to thousands of tiny lenses. Eyes like these are called compound eyes.
Imagine a dome covered in tiles. This is what the surface of a compound eye looks like. Each tile is a lens. If you could count all the tiles, you’d find that some kinds of lobsters can have as many as about 10,000 lenses.
Compound eyes are good at detecting motion. They are also good at gathering light under dim conditions. This is important, because lobsters live underwater, where it can be dark.
A lobster has gills at the base of its walking legs. Can you imagine breathing from your hips? Gills are feathery, blood-filled organs that extract oxygen from seawater. The blood from the gills travels to other parts of the lobster’s body, delivering oxygen along the way. Our lungs and circulatory system perform a similar task. A lobster must keep water moving across its gills—in the same way that humans must keep breathing—to maintain a steady supply of oxygen.
Not all crustaceans, however, have gills. Very small crustaceans with very thin “crusts” absorb oxygen directly through their shell. And, some land-living crabs breathe air with lungs instead of using gills to absorb oxygen from water.
Lobsters are not finicky eaters. They eat animals, such as fish or shellfish, as well as plants. Crowded into a tank, they may even snack on each other.
American lobsters are capable of catching small fish with their claws. They also hunt snails, sea urchins, and clams, crushing them with their claws.
Besides hunting live prey, lobsters scavenge the sea floor for dead and rotting animal carcasses, also known as carrion. Deep-sea lobsters, in fact, feed on the carcasses of whales, fish, and other dead animals. On land, large birds called vultures break down and recycle the nutrients of the dead creatures they eat. In the ocean, lobsters play this important role in recycling the sea’s nutrients.
If you look closely at a lobster, you can see that one of its claws is larger than the other. The larger, heavier claw has thick teeth for crushing prey. The smaller claw is like a steak knife. It has sharp teeth the lobster uses to seize and slice its food.
Not all lobsters have the larger claw on the same side. A lobster is “left-handed” or “right-handed” depending on which side has the larger claw.
A newly hatched American lobster has thousands of brothers and sisters. A female lobster can lay nearly 100,000 eggs at a time.
Unlike many other animals that lay eggs, a female American lobster does not deposit her eggs in a nest. She carries her eggs, holding them under her body attached to her swimmerets for 10 or 11 months. A sticky substance covering the eggs glues them together. When the eggs are ready to hatch, a female shakes her swimmerets, opening the tiny eggshells.
As a general rule, animals that reproduce in such large numbers do so because most of their offspring die young. Life is very dangerous for young lobsters. All sorts of fish, octopuses, and sea birds feed on young lobsters. So, although a lobster may begin life with many siblings, by the time it is an adult, most of them will have perished.
A newly hatched lobster looks like a see-through flea with huge black eyes. It is not a miniature version of an adult lobster. It first goes through a free-swimming stage. It is known as a larva (LAHR vuh) in that stage, and it is about 1⁄3 of an inch (0.8 centimeter) long. A larval lobster has a soft body and delicate, featherlike limbs. It propels itself by moving these limbs in a rapid rowing motion.
A newborn lobster spends its first two or three weeks of life swimming at the surface, feeding on tiny floating organisms.
During this time, it molts often. Each time it molts, the lobster becomes more like an adult lobster, growing a hard shell, jointed legs, and long antennae. By the time a lobster settles on the sea floor, it is ready to begin its life as a bottom-dweller.
Although an American lobster’s claws are formidable weapons, lobsters are shy and try to avoid conflict. Still, claws are often a necessary defense against a hungry octopus or codfish.
Another defense many kinds of lobster have is the ability to lose a limb. Lobsters and many other crustaceans can voluntarily detach a limb that has been grabbed by a predator. When a lobster loses a limb, it can sometimes grow another in a process called regeneration.
Spiny lobsters have developed a unique and interesting defense. Octopuses like to eat spiny lobsters. Moray eels like to eat octopuses. So, spiny lobsters sometimes share a den with a moray eel. If an octopus tries to prey upon a spiny lobster, its “bodyguard,” the eel, attacks and eats the octopus.
Lobsters belong to the class Crustacea of the phylum Arthropoda. The American lobster is Homarus americanus. There are several genera of spiny lobsters, including Palinurus, Panulirus, and Jasus.