Lobster Facts, Photos and Videos - Interesting Invertebrates
To many people, a lobster is simply a source of tasty meat that's fun to eat at social events. Living lobsters can be fascinating animals to observe and study, however. They deal with the problems of living very differently from humans. They have gills instead of lungs, different sense organs and a nervous system that has ganglia - nerve centers - but not a true brain. Nevertheless, lobsters are very successful creatures and are found in all oceans of the world.
My interest in lobsters began when I was at a high school event shortly after I arrived in Canada from the UK. A container of lobsters was present to feed the crowd. Another student told me that the live lobsters were going to be put into boiling water to cook, something that I had never heard of before. I was horrified and refused to eat any lobster meat. Boiling the animals alive seemed incredibly cruel to me. I did eat other types of meat, however. It didn’t occur to me that this too could have been seen as a form of cruelty to animals, depending on how the animals were treated and killed.
Today I enjoy exploring the lives of lobsters in the wild and examining the role of the living animals in their environment. Lobsters and other marine invertebrates are well worth studying.
The Lobster's Body - External Anatomy
A lobster's body is divided into two sections. The first is the cephalothorax, which contains the head and the thorax and is made of fused segments. The eyes, antennae and mouth parts are attached to the head, or cephalon, and the legs are attached to the thorax. The second body section is the abdomen, which consists of a visibly segmented region and a wider tail at the end. The underside of the abdomen has multiple pairs of swimmerets (or pleopods) attached to it, which help the lobster to move.
Lobsters are crustaceans and belong to an order of animals called the Decapoda. The order name refers to the ten legs, which are arranged in five pairs. The first pair of legs of many lobsters are greatly enlarged to form claws. One claw is larger than the other and is known as the crusher claw, while the smaller claw is called the pincer claw. These claws are used for manipulating objects but not for walking. Interestingly, some lobsters have the crusher claw on their right side while others have it on the left side, so lobsters have a form of handedness. The remaining four pairs of legs are the walking legs.
Lobsters usually move by walking along the ocean floor. When they're threatened they can swim backwards very rapidly, curling the underside of their abdomen and tail up toward the underside of the cepahothorax and then uncurling it again. Some reports claim that lobsters can move at up to five meters a second using this procedure.
A Caribbean Spiny Lobster Molting
The Exoskeleton and Molting
The lobster's skeleton is on the surface of its body instead of on the inside and is known as an exoskeleton or shell. As a lobster grows, it periodically sheds its exoskeleton in a process called molting. ThIs is necessary because the exoskeleton is too hard to allow the lobster's body to expand.
The lobster that emerges from the old shell is in a very delicate state. It's covered by a new exoskeleton that formed under the old one, but this new covering is soft and needs time to harden. The softness of the new shell allows the lobster's body to increase in size but also makes the animal vulnerable to predators. In the wild, molting generally happens in a secluded place, such as a burrow.
Not all animals with "lobster" in their name are true łobsters. True łobsters belong to the family Nephropidae. Spiny lobsters, squat łobsters and slipper lobsters don't belong to this family. The molting process of the spiny lobster that's shown in the video above is quite similar to that of a true lobster, however.
Classification of the American Lobster
The American Lobster
The American lobster (Homarus americanus) lives on the east coast of North America in Canada and in the United States. Most American lobster shells are olive green or red brown in color. The shell may have orange highlights, however, and may sometimes have blue markings around the joints. Very rarely, an American lobster is completely blue. Even rarer are red lobsters. Yellow lobsters are extremely rare. Albino lobsters - those with no pigment - also exist.
Blue, Yellow and White American Lobsters
According to the Lobster Institute at the University of Maine, an estimated one in two million American łobsters is blue, one in ten million is red and one in thirty million is yellow. The frequency of calico lobsters is also one in thirty million.
A Calico or Orange and Brown Lobster at the New England Aquarium
Lobster Senses - Sight and Hearing
The eyes of lobsters are located at the ends of little stalks and are movable. Lobsters have compound eyes which give them a 180 degree view of the world. It’s thought that the eyes are sensitive to light intensity and movement but don’t produce a very clear image.
Lobster eyes are interesting because they contain mirrors instead of lenses. Each of our eyes - and the eyes of most other animals - contains a lens that refracts (bends) light rays so that they hit the retina, the light-sensitive layer at the back of the eyeball. The lobster eye is made of many sections, each containing a reflective surface that acts as a mirror instead of a lens. The mirrors reflect the light rays on to the light-sensitive layer of the eye. Lobsters don't have color vision.
"Sound" is created by vibrations at the specific frequencies that an ear can detect. When the ear is stimulated it sends a signal to the brain, which creates the sensation of sound. Lobsters almost certainly can't sense sounds in the way that we do, since they don't have any sense organ that behaves like our ears. They do detect vibrations, however. They also produce low frequency vibrations themselves by contracting and relaxing special muscles at the base of their antennae. This causes the carapace - the exoskeleton over the cephalothorax - to vibrate. The function of these vibrations is uncertain, but they may play a role in defence.
A Yellow Lobster
Smell, Taste and Touch
Lobsters have an excellent sense of smell. They use the first, shorter pair of antennae to detect scents. These short antennae, which each consist of two branches, are actually known as antennules. The many tiny hairs on the antennules pick up a wide range of odors.
The mouth parts and the legs of a lobster have taste receptors. The second, longer pair of antennae are sensitive to touch. The exoskeleton has fine hairs which also sense touch.
A Giant Lobster
Above the walking legs on each side of a lobster’s body is a space under the exoskeleton called the branchial chamber (or sometimes the gill chamber). The lobster’s gills are located in these chambers. If the shell on the side of a lobster is removed, the gills can be seen. The branchial chamber is lined with a thin layer of shell on its inner wall.
The internal anatomy of a crayfish is very similar to that of a lobster. In the crayfish anatomy video below, the gills are shown, although the narrator never refers to them. The gills are the segmented clumps of tissue on each side of the crayfish above the walking legs. They look like clumps because they are dried out and stuck together. When the gills are placed in water they separate, revealing a feathery structure.
There are twenty gills in each branchial chamber of a lobster. Each gill consists of a central rod with projections extending all around it. Most of the projections are long and look like filaments. The gill is often said to resemble a bottlebrush. The base of each gill is attached to the wall of the branchial chamber or to the legs. Therefore when a leg is removed from a lobster a gill may be removed as well.
Internal Anatomy and Gills of a Crayfish, A Lobster Relative
Sea water reaches the gills through the opening at the bottom of the branchial chamber. As the water moves upwards and forward over the gills, the gills extract oxygen from the water. The oxygen is then transported by the blood to the lobster's cells. The blood picks up carbon dioxide waste from the cells and transports it to the gills, where the carbon dioxide is released into the water that is flowing over the gills. The water in a branchial chamber moves out through an opening at the front of the chamber.
The current that moves the water over the gills is created by a structure called the gill bailer, or scaphognathite. This is a flap attached to a mouth part and is almost constantly beating. Sometimes the gill bailer changes the direction of its beat for a short time in order to reverse the direction of water flow and sweep sea water over the gills, removing any debris that has become trapped on them.
Internal Anatomy of a Lobster
More Facts about Lobsters
- Lobsters aren't scavengers, as was once thought. They prefer to catch live prey, such as fish, crabs, clams, snails and starfish.
- A lobster has two stomachs. The first is called the cardiac stomach and the one behind it is called the pyloric stomach.
- The teeth of a lobster are in its cardiac stomach, which is close to its mouth. The teeth form a structure called the gastric mill.
- The tomalley from a lobster is a soft and green material which some people consider very tasty. It may collect toxins, however, and should be eaten with caution. Tomalley is actually the digestive gland of the lobster, which plays a role somewhat similar to that of our liver and pancreas.
- Lobsters have an "open" circulatory system. Their heart pumps blood into arteries, but the arteries lead to blood cavities called sinuses instead of to other blood vessels. The blood travels through sinuses and channels back to the heart.
- Lobsters have colorless blood, which turns slightly blue when exposed to oxygen.
- Lobsters can regenerate their claws, their walking legs and their antennae. They may drop a claw spontaneously, which is useful if they want to escape from a predator.
The Lobster's Nervous System
A lobster's nervous system is based on ganglia and nerves. These are made from neurons. A neuron consists of a cell body, whIch contains most of the cell's organelles, and a fiber called an axon extending from the cell body. A ganglion is a group of cell bodies from several neurons. A nerve is a group of axons bundled together.
A lobster has a large pair of ganglia in its head near its eyes, which is sometimes referred to as a brain. These ganglia don't have the complex structure of a true brain, however. A double nerve cord extends from the "brain" to the lower part of the lobster’s body and then travels towards the rear of the animal. The nerve cord has a pair of ganglia in almost every segment of the lobster and gives off nerves that go to the various parts of the body.
Do Lobsters Feel Pain?
Do lobsters and their relatives feel pain? Researchers can't answer for certain. There are scientists on both sides of the debate. Some claim that lobsters and other invertebrates do feel pain and stress; others say that it's "unlikely" that they feel pain due to their relatively simple nervous system.
To me it seems highly unlikely that lobsters and other invertebrates have evolved without being able to perceive some kind of pain sensation. As the first linked article points out, feeling pain is a protective mechanism to prevent damage to an organism's body. The brain of lobsters doesn't have a cerebral cortex, the part of our brain that perceives pain. This doesn't rule out the possibility that lobsters are perceiving pain by a different mechanism than we use. In any case, since no scientist can guarantee that lobsters are unable to feel pain, the onus should be on us to kill them humanely if we want to eat them.
In the American lobster (Homarus americanus), the female releases a pheromone to attract a male. The male's first pair of swimmerets are rigid and grooved. They are used to insert sperm into the female's sperm receptacle.
The female retains her unfertilized eggs in her body for many months. Eventually she releases her eggs, which are fertilized by the sperm and then stick to her swimmerets. Here they stay until they hatch.
Some Lobster Statistics
- In 2006 a teenager in the United Kingdom caught (and released) a giant lobster weighing 11 pounds 3 ounces. Experts think that the animal could have been as old as fifty years of age. There are claims that far heavier lobsters than this have been caught, including a 22 pound specimen and a 44 pound, three and a half foot long animal that is reported to have been caught off the coast of Eastern Canada in 1977.
- Lobsters are thought to be able to live for up to a hundred years.
- Lobsters can live out of water for one or two days if they are kept cool and their gills stay moist.
There are probably many more facts about lobsters to be discovered. They are interesting animals to observe.
© 2012 Linda Crampton