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LOBSTER BRAIN
Lobsters have simple brains. A lobster brain consists of a dense collection of nerves called a ganglion. The ganglion sits at the end of a long string of nerve fibers that connect the brain to the rest of the lobster's body. The combination of the brain and these long nerves is called the central nervous system.
As with other animals, the lobster's central nervous system transmits tiny electrical messages between the different parts of the body and brain. For instance, nerves in the lobster's legs, eyes and shell are constantly sending messages to the lobster's brain about its environment. The brain, in turn, sorts through these messages and reacts automatically to those messages requiring some kind of action. This type of response is called an INSTINCT because the lobster doesn't actually think about the action before doing it. If the lobster's eye sends a visual message to the brain, say, that a fast-moving object is approaching, the lobster's brain might respond by sending an electrical message to the tail, "telling" the tail to close rapidly and propel the lobster to safety.
ÇLobster Gills
LOBSTER GILLS
The gills of a lobster function much the way a fish's gills do. Each gill is made of a fine, feathery material that is filled with tiny blood vessels. The gills are attached near the area where a lobster's legs are attached to the body. The movement of the lobster's legs helps bring water to the gills. As the water passes over the gills, the blood vessels in each gill absorb the oxygen from the water and release carbon dioxide, which is a byproduct of respiration. The oxygen is then carried in the blood to the other parts of the lobster's body, where it is used for activities such as movement, growth and digestion.
∙Lobster Gonad
LOBSTER Gonad
This long, colorful organ is called a gonad. It is used by lobsters for reproduction. In female lobsters, the gonad produces eggs. In male lobsters, it produces sperm. Like most other invertebrates, lobsters reproduce by laying and fertilizing eggs. Once a lobster's eggs are fertilized, they are kept in a small chamber attached to the lobster's body. Several weeks later, baby lobsters, known as larvae, emerge from the eggs.
During the larval stage of its development, a lobster looks nothing like it will as an adult. Instead of having a long body with a shell and claws, the lobster larva is almost circular, and it has no tail or recognizable head. Without any means of moving around, a lobster larva must float along in the ocean current. Most lobster larvae end up as a meal for some other animal. As the larva grows, it sheds its outer layer of skin. This process is called MOLTING. With each molting, more of the lobster's parts are revealed until a recognizable lobster finally appears.
,Lobster Heart
LOBSTER HEART
The lobster's heart acts like a small pump which draws oxygen-rich blood from the gills and then pumps it to the rest of the lobster's body. The blood is carried through a web of connecting blood vessels called a circulatory system. In lobsters, blood flows from the lobster's body tissues into a large body cavity, known as a hemocoel, located near the middle of the lobster. From the hemocoel, the lobster's blood flows into the gills, where carbon dioxide is released by the lobster's blood cells and oxygen is absorbed from the water.
rLobster Stomach
LOBSTER STOMACH
Lobsters don't have just one stomach, but two. Like many animals, the lobster digests its food in stages. Food passes through the mouth into a straight digestive tract. From the digestive tract, the food moves into a large stomach known as the cardiac stomach where it is broken down into smaller pieces. Following the cardiac stomach, the food enters a second stomach where digestive juices known as enzymes break down the food into even smaller pieces that can now be easily absorbed by the lobster's blood cells. These enzymes are produced by a large gland, located nearby, known as the digestive gland.
gOctopus Brain
OCTOPUS BRAIN
The octopus's brain is one of the largest, most complex brains of all invertebrates. It is enclosed in a thick, protective layer of cartilage located just behind the octopus's eyes.
The octopus's brain is divided into several areas known as lobes. Each lobe is connected to parts of the octopus's body by long, thick nerve fibers. The lobes of an octopus's brain monitor and control millions of tiny electrical impulses that travel between the brain and the different parts of the octopus's body. These impulses tell the brain what is going on both inside and outside the octopus's body. At the same time, the brain is sending messages to the rest of the body, telling it what to do.
One of the largest lobes in the octopus's brain is called the visual lobe. It is connected to the eyes and keeps track of all the visual information being transmitted to and from the octopus's eyes. Another large lobe in the brain is responsible for the messages coming from the octopus's arms and suction cups. Octopuses rely heavily on their ability to feel and manipulate objects, so this part of the brain is very large. Unlike most undersea animals, the octopus's brain is capable of remembering things. An octopus can actually learn from its experiences, remembering to avoid places where predators live or remembering to go to places where there is an abundance of food.
LOctopus Gills
OCTOPUS GILLS
The gills of an octopus are located safely inside the octopus's body cavity. Like a fish's gill, an octopus's gill is made of a feathery material that is filled with tiny blood vessels. To capture oxygen from ocean water, the octopus draws water into its body through a small muscular opening called a funnel. The water then passes over the octopus's gills, where oxygen is absorbed by the octopus's blood cells and carbon dioxide is released. At this point, the tiny atoms of oxygen latch onto different blood cells and are then transported all over the octopus's body.
ÄOctopus Heart
OCTOPUS HEART
The function of an octopus's heart is to pump oxygen-rich blood from the gills to the rest of the octopus's body via a network of blood vessels known as a circulatory system. The octopus's heart is divided into two chambers: an atrium, which collects blood from the body; and a ventricle, which pumps blood out to the body. Like all hearts, the octopus's heart pumps rhythmically, either contracting to push blood out of the heart or relaxing to let blood flow back into the heart. The octopus's circulatory system is similar to that of a crab or a shellfish. Blood flows from the body tissue through vessels known as veins into a large body cavity called a hemocoel. The blood then passes through the gills where it absorbs oxygen from the seawater. After this stage, the blood travels to the heart where it is pumped back out to the rest of the body through blood vessels known as arteries.
▐Octopus Mouth
OCTOPUS MOUTH
Octopuses have strong, beak-like jaws that are so powerful they can crush the shells of very large crabs and lobsters. When an octopus captures its prey, it holds the animal in its mouth, then kills or paralyzes it with a poison that is secreted by the octopus's salivary glands. The octopus then injects into its prey's body a digestive enzyme that dissolves many of the animal's toughest body tissues. Once the animal's body is soft enough, the octopus sucks it into its mouth. Because the octopus dissolves most of its food outside of its body, it only needs a simple digestive system to absorb food into its bloodstream. A few hours after an octopus captures a crab or lobster, all that's left is an empty shell.
-Octopus Stomach
OCTOPUS STOMACH
Unlike many animals, the octopus does most of its digesting outside the body. For this reason, the octopus only has a small, simple stomach.
Many animals need food to be in their digestive system for several stages stages of digestion. This helps break down the food into pieces small enough to be absorbed into their body's bloodstream. The octopus is different. It injects digestive enzymes into its food before the food even enters its mouth. These enzymes work like acids, dissolving the tough parts of the food so that it can be quickly and easily digested by the octopus's stomach. Located very close to the octopus's stomach is a small ink sac. When an octopus is in danger, it will often squirt ink out of its body, creating a murky cloud in the water that helps confuse an attacker.
£Shark Reproduction
SHARK REPRODUCTION
Most sharks give birth to live young rather than lay eggs, as most fish do.
Scientists know very little about the mating habits of sharks. Since sharks range over such wide areas of ocean, it must take a long time for male and female sharks to find one another. When they do, the male chases the female, often biting her tail to get her interested in mating. Once the male catches the female, he fertilizes her eggs by inserting one of his fins, known as a clasper, into an opening in the female's body.
In most shark species, the fertilized eggs reside inside a cavity in the female's body known as an oviduct. Safe inside the oviduct, the shark embryo is nourished by a yolk sac attached to its body. Some shark embryos actually feed on unfertilized eggs inside the female's body. After a period of four to eight months, the embryos hatch but continue to remain inside the oviduct while the baby shark keeps growing. Eventually, the female shark gives birth to live baby sharks. Unlike mammals, sharks do not care for their young. Once they are born, baby sharks swim away to fend for themselves.
A small number of sharks like the dogfish or swell shark reproduce by laying eggs. Just after the female's eggs are fertilized, they are covered with a leathery shell which resembles a small purse. The egg is then deposited in a safe spot on the sea floor, where it will remain for as long as a year. Safe inside the shell, the shark embryo lives off of a yolk sac that is connected to its body by an umbilical cord. When the shark finally hatches from its egg, it is quite vulnerable to attack by predators and must quickly find a hiding place until it is larger.
kShark Brain
SHARK BRAIN
For many years it was thought that sharks had simple, primitive brains. Yet recently, scientists have shown that many sharks have large, capable brains, especially when compared to other vertebrates. Certain sharks have even demonstrated the ability to learn simple tasks.
A shark's brain is the center of a complex system of nerves and senses. Millions of tiny electrical messages are transmitted to the brain from all over the shark's body. For instance, the shark's eyes are constantly sending information to the brain about what is visible to the shark. Electrical sensors in the shark's face transmit information about the electrical fields being created by other animals in the water. At the same time this is happening, the shark's brain is sending messages out to the different parts of the body, instructing them what to do.
Brains differ greatly in size and complexity from one shark species to the next. Large, fast-moving sharks like the hammerhead and dusky shark have bigger brains, probably because they spend more time hunting and tracking prey. Slower, bottom-dwelling sharks, which find most of their food in one place, generally have smaller brains.
Shark brains are divided into three large segments: a forebrain, a midbrain and a hindbrain. Each of these segments is responsible for controlling a different part of the shark's bodily functions.
▄Shark Heart
SHARK HEART
Like other fish hearts, the shark heart is made of four chambers composed of a powerful muscular tissue. The chambers work together to collect blood from the shark's body, then pump it to the gills where it is enriched with oxygen.
Once the blood has passed through the gills, it is pumped back out to the shark's body. Blood vessels known as veins transport the blood from the shark's body to the heart. Vessels known as arteries carry the blood out of the heart to the gills, then back to the different parts of the shark. The size of the heart depends on the kind of shark it belongs to. Highly active sharks such as the mako or grey shark have larger hearts than do slower sharks, which remain in a small area.
≡Shark Stomach
SHARK STOMACH
All sharks are big eaters. And because they are big eaters, they need a large stomach to hold their food. Some sharks keep more than just food in their stomach. The stomachs of many captured sharks have included items such as cans, shoes--even tires.
Most sharks eat once every one or two days. It usually takes 24 hours for a shark to fully digest its food. Some sharks, like the great white shark, can eat a single enormous meal and then wait as much as two months before feeding again. Once a shark's food is swallowed, it enters the stomach where it is broken down by digestive enzymes into small pieces that are more easily digested. After the food moves through the stomach, it passes into the shark's intestine, where much of it is absorbed by the shark's blood and used as fuel for the shark's physical activities.
Just below the shark's stomach is its liver. Almost all sharks have an enormous liver to help them remain buoyant in the water. Unlike other fish, sharks do not have a swim bladder, which helps to keep a fish's body stable in the water. To make up for this, the shark's large liver is filled with oil that is lighter than water so the shark actually can float. Some shark's have livers that weigh as much as 200 pounds.
ÖLobster Gills
LOBSTER GILLS
A lobster's gills are located near the spot where its legs are attached to its body. Lobsters collect oxygen from the water and into their gills by constantly waving their legs. After oxygen has been removed from the water by the gills, the oxygen passes out of the lobster's body through an opening near its mouth. The female lobsters carry their eggs between their gills and lower abdomen.
╛Lobster Antennae
LOBSTER ANTENNAE
The lobster's long, sensitive antennae are used to help it learn about approaching objects. Lobsters wave their antennae in front them as they walk. The antennae tell the lobster whether to attack or retreat. Some lobsters have antennae that are so sensitive that they can "smell" certain kinds of undersea life forms. Other lobsters use their antennae to churn up the water in front of them and draw food toward their mouth.
Lobster Shell
LOBSTER SHELL
A lobster's shell is very hard and covered with sharp spines, which are used to ward off enemies. This shell is made up of different pieces that are connected to each other at joints around the lobster's body. Every three to four months, a lobster outgrows its shell and must replace it with a new one. When this happens, the lobster's old shell becomes soft and falls off its body. It then takes three to four hours for the lobster's new skin underneath to harden. During this time, the lobster is almost completely helpless and often hides deep in caves so that it will not become a tasty treat for some lucky predator.
Lobster Pincer
LOBSTER PINCER
The large claws or pincers are found on the first of five walking legs on each side of the lobster. They are used for moving over the ocean floor, and for grasping food while it is being torn apart. A lobster's pincer is loaded with muscle, giving the lobster a powerful grip. Each pincer is also equipped with strong, stiff bristles at the tips for grasping. Often, lobsters will lose a large pincer in combat with a predator or another lobster. Some lobsters can grow back the lost pincer in several months.
Lobster Eyes
LOBSTER EYES
A lobster's eye is located at the end of a long, movable stalk. The eye has a hard, curved surface that is made up of thousands of tiny lenses. Each of these lenses acts like a separate eye, detecting differences in light and dark. Some lobsters are capable of seeing certain colors such as blue and green. Because the surface of a lobster's eye is so large, lobsters see movements over a very wide angle, like the wide-angle lens of a camera. Lobsters are probably able to make out the forms and shapes of different objects.
8Lobster Tail
LOBSTER TAIL
The lobster has strong muscles in its tail which can pull the tail down and forward very quickly. This movement can propel the lobster backward at high speeds by pushing the water beneath the tail forward. When threatened, a lobster will often use its tail to move backward and away from danger.
2Octopus Arms
OCTOPUS ARMS
An octopus has eight flexible and muscular arms. Each of these arms has suckers on the inside edges and is used both for walking over the ocean floor and for holding onto prey when the octopus is eating. An octopus's arms are highly sensitive to touch and can manipulate very small, fragile objects. The inside of each of an octopus's suction cups is lined by nerves that can detect the differences between the tiniest shapes. Female octopuses will often spend months moving and cleaning their fragile eggs, and none of the eggs will be damaged.
ROctopus Eyes
OCTOPUS EYE
Unlike many undersea hunters, the octopus relies almost entirely on its vision to find and catch prey. For this reason, the octopus's eye is highly developed and can probably see images nearly as well as a human eye can.
Much of an octopus's brain is devoted to interpreting the many signals coming from the octopus's eyes. The octopus eyeball is flattened like a fish eye. To focus on an object, the lens of the eye moves rapidly back and forth. The eye of an octopus is also quite large, making it easy for the octopus to see well at night, when it does most of its hunting.
╚Octopus Funnel
OCTOPUS FUNNEL
An octopus's gills are enclosed in a large muscular chamber called a funnel. This chamber pumps water in and out and over the gills. When the octopus is in danger, the chamber squeezes water out in a powerful gush, jetting the animal backward. An internal ink sac also opens into this chamber. An octopus will squirt ink out to confuse an invader. The ink is irritating to many undersea animals and makes it hard to see what is going on.
&Octopus Body
OCTOPUS BODY
The octopus's large, muscular body may look like a head but in fact it contains all of the octopus's organs, such as the stomach, kidney, gills and brain. Unlike the bodies of many undersea animals, the octopus's body completely lacks a shell or bones of any kind. It does have a soft, cartilage-like substance that forms a protective layer around the brain.
The skin of an octopus is well known for its ability to change colors quickly in order to match the octopus's surroundings. This is possible because the octopus has many different kinds of colors, called "pigments", in its skin. The pigments are held in a small sac just under the skin. By using its nerves and muscles, the octopus can control how much of this pigment is released into its skin, thereby changing its appearance.
σOctopus Mouth
OCTOPUS MOUTH
The mouth of an octopus is located where its tentacles attach to its body. The opening of the mouth has a small, parrot-like beak. This beak is quite powerful and is used for tearing apart food, such as crabs and lobsters. Salivary glands near the beak secrete fluids that help break down the food into smaller pieces. In some species of octopus, this fluid is very poisonous. A few people have died from the bite of a small blue-and-purple-ringed Australian octopus.
÷Octopus Suckers
OCTOPUS SUCTION CUPS
An octopus has suckers that cover the inside of all eight of its arms. These suckers make it possible for the octopus to get a good grip while climbing over slippery rocks. They also help to hold onto prey while an octopus is eating. An octopus's suckers are round and fleshy, and each one has its own circular muscles which help create a suction action. The octopus's suckers are also ringed by many sensitive nerves that can detect the differences between very small objects.
uShark Eyes
SHARK EYES
Contrary to what many people think, sharks have excellent eyesight. A shark's eye can see well during the day and also at night, when many sharks feed. Sharks' eyes are built very much like human eyes, except that they are much thinner. The shark eye is composed of three chambers: an iris, a lens and a retina. The size of the eye depends on what kind of shark it is and where it lives. Sharks that live in shallow waters, where there is plenty of light, have smaller eyes. They don't need to capture a lot of light in their eyes to see. Sharks that live in deeper waters, such as the mako shark, have much larger eyes to capture as much light as possible.
To help see in very dark water, sharks also have a special reflective lens that is located at the back of their eyeball, just behind the retina. This lens acts like a mirror, reflecting small amounts of light in the shark's eye many times over. It is believed that most sharks see in black and white, but it's possible that a few sharks also see in color.
Ears are not found on the outside of sharks or on any other fishes. However, sharks still have very good hearing, particularly for low-frequency sounds like those made by struggling fish. The shark's ear consists of a small membrane of skin that is attached to a spot near the top of the head. This piece of skin moves every time there is a vibration in the water.
╪Shark Dorsal Fin
SHARK DORSAL FIN
Nothing strikes fear in the heart of a swimmer more than the thought of a shark's dorsal fin breaking the surface of the water nearby. This highly recognizable fin acts like a sailboat's keel, stabilizing the shark's body when it is moving through the water. Without the dorsal fin the shark would begin turning to one side, something known as side-slipping. Unlike a shark's other fins, the dorsal fin is stiff and immovable. It is also considered a delicacy in dishes such as shark fin soup.
The shark's pectoral fins are flexible. They can be moved up and down to help steer the shark left and right and up and down. These fins also help communicate the kind of mood a shark is in. When the pectoral fins are in the downward position, the shark is in what scientists and divers call a "threat" posture. This means that the shark may be ready to attack. Divers have learned to avoid and carefully retreat from sharks with their pectoral fins in this position.
=Shark Gills
SHARK GILLS
Like other fish, sharks use gills to remove the oxygen they need from the water. A shark's gills are made up of a feathery material that is packed with tiny blood vessels. As water enters the shark's mouth and passes over the gills, the blood vessels in the gills absorb oxygen from the water and release carbon dioxide. The water then exits through a shark's gill slits. Most fish have only one gill slit, but sharks have between five and seven.
To keep breathing like this, most sharks must keep moving forward so that they maintain a constant flow of water through their mouth and over their gills. If these sharks stop swimming for long periods of time, they will suffocate. Other sharks, such as those that live on the ocean bottom, have muscles which pump water rhythmically over their gills at all times.
Shark Mouth
SHARK MOUTH
A shark's mouth is perfectly suited to a lifestyle of hunting and eating. The shark's head and neck are covered with giant muscles that give a shark its powerful bite. The upper jaw of most sharks is only loosely connected to the shark's skull. This allows many sharks to extend their upper jaw outward, thereby making it easier to take large bites out of their prey. A shark's teeth differ in size and shape depending on the type of shark. The bull shark, for instance, has small teeth which are good for chewing up crabs and mollusks. The great white shark has large, serrated teeth that can saw off large pieces of flesh.
Shark teeth are not attached directly to the jaw of a shark, as they are in many animals. Instead, the teeth grow in a groove known as a "tooth bed," where they move from the back to the front. When broken or lost, a brand new tooth rotates up from behind in just a few days replacing the lost or damaged tooth. Sharks have such powerful bites that they often break or lose teeth.
#Shark Skin
SHARK SKIN
A shark's skin looks smooth but is in fact very rough, like sandpaper. That's because the skin is covered with small, tooth-like bumps called "denticles." These bumps feel smooth when they are stroked from front to back, but feel very prickly when stroked in the reverse direction. Some people think that these bumps slow a shark down by creating friction with the water. Actually, the ocean water flows through channels between the bumps in such a way that they reduce friction, helping the shark to swim more efficiently. Unfortunately, many divers have gotten very bad scrapes from a passing shark whose skin rubbed them the wrong way. Before the invention of sandpaper, shark skin was widely used for an abrasive and for polishing.
Running the length of a shark's body is a row of small receptors called the "lateral line canal." This canal is made up of tiny sensors that detect small changes in the water pressure nearby. Without seeing or smelling a moving fish, a shark's lateral line canal would be capable of detecting its presence.
╕Shark Snout
SHARK SNOUT
One of the shark's most highly developed senses is its ability to smell. A shark's nostrils consist of two small nasal sacs that have no internal connection to the mouth or throat. These nasal sacs are made up of very tiny rows of folded skin which can detect even the tiniest quantities of certain chemicals in the water. Some sharks are able to smell one molecule of blood in a billion molecules of seawater. This is quite helpful for sharks that feed at night and must track the scent of an injured fish for long distances in murky water.
A shark's other remarkable sense is its ability to detect very weak electrical currents in the water. The shark does this by using tiny receptors called "ampullae of Lorenzini" that are hidden just under the skin of a shark's snout. These receptors are made of jelly-filled canals connected to the surface of the skin by tiny, sunken cups that look like small pin pricks. Using these receptors, a shark can detect the tiny electric field created by an animal in the water. It is also believed that sharks use their electrical receptors to find out where they are in the water in the same way that people use compasses to know which direction to go.
Shark Tail
SHARK TAIL
The shark's tail, or "caudal fin," is used to propel the shark forward in the water. In almost all sharks, the upper lobe of the tail is larger than the lower lobe. The longer tail lobe helps push the shark's body downward into the water. For support, a long extension of the backbone extends up and back through the upper lobe of the tail. The size and shape of a shark's tail differ from species to species. Most slower-moving sharks have larger upper tail lobes. For example, the bottom-dwelling catshark has a long flat upper lobe, while the great white and mako sharks have upper and lower lobes that are equal in size. This is the sign of a fast, efficient swimmer. The thresher shark has an extremely long upper lobe that is actually used to slash its prey.
