Of the million or more animal species in the world, more than 98% are invertebrates. Invertebrates don’t have an internal skeleton made of bone. Many invertebrates have a fluid-filled, hydrostatic skeleton, like the jelly fish or worm. Others have a hard outer shell, like insects and crustaceans. There are many types of invertebrates. The most common invertebrates include the protozoa, annelids, echinoderms, mollusks and arthropods. Arthropods include insects, crustaceans and arachnids.


Protozoa are simple, single-celled animals. They are the smallest of all animals. Most protozoa are microscopic in size, and can only be seen under a microscope. However, they do breathe, move and reproduce like multicelled animals.

There are several types of protozoa. The amoebas are clear, shapeless cells. Flagellates have a body shape looking like a hair.

Although we can’t see them, protozoa do a lot for us. Protozoa play a useful role in the food chain as a source of food for fish and other animals. Some protozoa are helpful to humans by eating dangerous bacteria. Unfortunately, other protozoa are parasites and can be harmful to humans by transmitting disease. 

Protozoa eat tiny algae and bacteria. Some protozoa absorb food through their cell membrane. Others surround and engulf their food or have openings to collect food. They digest their food in stomach-like compartments called vacuoles.

Protozoa take in oxygen and give off carbon dioxide through the cell membrane.

Protozoa reproduces by splitting in half.

Now, try to know more about protozoa through this funny activity!


There are about 9,000 species of Annelids known today, including worms and leeches. They can be found almost anywhere in the world. Annelids have existed on Earth for over 120 million years.

Annelids have bodies that are divided into segments. They have very well-developed internal organs. One common characteristic of annelids is that they don’t have any limbs.

Some annelids may have long bristles. Others have shorter bristles and seem smooth, like the earthworm shown here.

There are many types of worms. Commonly known worms include earthworms, roundworms and flatworms. Most worms are small, measuring fractions of an inch to several inches long. Other worms, such as the ribbon worm, can grow up to 100 feet in length. Some worms are considered parasites, in that they live inside the human body.

Pay attention to the anatomy of annelids!


Mollusks were among the first inhabitants of the Earth. Fossils of mollusks have been found in rocks and date back over 500 million years. Mollusk fossils are usually well preserved because of their hard shell.

Most mollusks have a soft, skin-like organ covered with a hard outside shell. Some mollusks live on land, such as the snail and slug. Other mollusks live in water, such as the oyster, mussel, clam, squid and octopus.

Land living mollusks, like the snail, move slowly on a flat sole called a foot.

Ocean living mollusks move or swim by jet propulsion. They propel themselves by ejecting water from their body. For example, the squid ejects water from a cavity within its body, and the scallop ejects water to move by clamping its shell closed.

Other ocean living mollusks, like the oyster, attach themselves to rocks or other surfaces, and can’t move. They feed by filtering small food particles from water that flows through them.

Here, you will find interesting videos about different mollusks:

The clam is native to many of the world’s oceans and freshwater rivers. There are many different types of clams. For example, the Pacific Razor Clam is found along the Pacific west coast of the United States. The Asian Clam is found along sea coasts and estuaries in northern Europe, the Mediterranean and west Africa. The Giant Clam is found in coral reefs of the South Pacific and Indian Oceans. A clam’s shell consists of two parts connected by a hinge joint. The hinged joint allows the clam to open and close its shell to feed and protect itself from predators.

Despite their name, the cuttlefish is not a fish, but a mollusk. The cuttlefish is native to all of the oceans of the world, but are more common in shallow coastal temperate and tropical waters. The cuttlefish has an internal shell or bone, called the cuttlebone, that helps them to be buoyant. Attached to this body structure is the head with eight arms and two feeding tentacles. The cuttlefish can easily camouflage itself by changing its skin color and pattern to blend in with its background. This helps the cuttlefish to hide from predators, and the sneak up on its prey. Like the squid and octopus, the cuttlefish can eject ink in an effort to escape from predators. This ink, called sepia, was once used as a die to create ink used by artists.

The nautilus is native to deep ocean waters. It has a multi-chambered shell. Each chamber is sealed and contains gas which provides the nautilus with buoyancy to float. Like the octopus, squid and cuttlefish, the nautilus uses jet propulsion to move forward. It sucks in water, then expels it in a fast, strong stream to propel itself forward. The nautilus has as many as 90 small tentacles that it uses to catch food, such as shrimp, fish or small crustaceans. It then uses its powerful beak to crush the food. The nautilus is considered a living fossil because its form has remained unchanged for over 400 million years.

There are about 300 different species of octopus native to many of the world’s oceans, especially coral reefs. The octopus doesn’t have an internal or external skeleton, allowing it to squeeze into very small places. The octopus has eight arms or tentacles, that it uses for crawling, exploring things and catching prey. The octopus’ arms have suckers capable of grasping and holding objects, such as their prey. The octopus has a hard beak in the center of its arms that it uses to tear apart its prey for eating. Like the squid, the octopus can suck water into its mantle and expel it out in a fast, strong jet. This jet propulsion provides fast, forward movement. Also like the squid, the octopus can eject a thick cloud of ink to help it escape from predators.

Oysters are a family of bivalve mollusks like the clam, mussel and scallop. This means they have two half shells connected by a hinge that allows the oyster to open and close its shell. Oysters are native to many of the world’s oceans and bays. Oysters are a very popular sea food. Oysters are also harvested by people for their pearls. Unfortunately, many of the world’s oyster reefs have been destroyed by overfishing and coastal development. Due to the massive loss of oyster reefs, many states have oyster restoration projects in an attempt to revive the oyster population.

The snail family consists of marine snails and land snails all over the world. Land snails live in many habitats from gardens and woodlands, to deserts and mountains. Marine snails are native to all the worlds oceans and seas, and many freshwater rivers and lakes. Along with slug, snails make up the gastropod class of the mollusk phylum. Snails have an external shell, large enough to withdraw their body into it. Gastropods without a shell are known as slugs.

There are about 300 species of squid. They are native to most of the world’s oceans. The squid has a distinct head, eight arms and two tentacles. The mouth of the squid has a sharp horny beak used to kill and tear its prey into small pieces. The main body of the squid is enclosed in the mantle, which has a swimming fin along each side. However, the swimming fin is not the squid’s main way of moving through the water. The squid can suck water into the mantle and expel it out in a fast, strong jet. This jet propulsion provides fast, forward movement. Although most squid are less than 2 feet in length, the giant squid can grow up to 43 feet in length.


Echinoderms are marine animals that live in the ocean. Common echinoderms include the sea star, sea urchin, sand dollar and sea cucumber. Most echinoderms have arms or spines that radiate from the center of their body. The central body contains their organs, and their mouth for feeding.

Sea stars, commonly known as the starfish, have 5 or more arms attached to their body. On the bottom of the Starfish are small tube feet to help with movement and feeding. The starfish’s mouth is underneath, and is capable of eating other sea life such as clams and mussels.

Another type of echinoderm is the sea urchin. Sea urchins have many spines connected to their body. These spines help to protect them from predators.

-Do you want to learn more about echinoderms? Watch the following videos. They’re fantastic!

The sand dollar habitat is the sandy or muddy ocean floor of coastal areas and bays. Dead sand dollars are often found washed up on beaches. They are called sand dollars because they look like a large, round, flat coin. Alive however, sand dollars look like fuzzy cookies. Sand dollars have tube feet on their top and underside. They use the underside tube feet to move around on the ocean floor. Their mouth is also on their underside. They sift through the sand using their tube feet to find food.

There are about 1,250 species of sea cucumber native to ocean floors throughout the world. They inhabit everywhere from shallow waters to deep seas, and often travel in large herds. Their name comes from the fact that many of these species look much like a cucumber. The sea cucumber is a scanvenger, feeding on plankton and decaying organic matter found on the ocean floor. They sift through this sediment with their tentacles. They also position themselves in currents to catch food that flows by their open tentacles. When threatened, some sea cucumbers discharge sticky threads or eject some of their internal organs to deter their predator.

Sea urchins are small, spiny, ball-shaped creatures usually found on rocky ocean bottoms. Spines cover most of the sea urchin’s body. These moveable spines are used for both walking along the ocean floor, and for protection from predators. Some sea urchin spines are also poisonous, to further protect against predators. Sea urchins have rows of tiny tube feet used to move along the ocean floor and collect food. On its underside is a claw-like mouth with five sharp teeth used to feed on algae or small invertebrates, such as mussels.

The starfish or sea star is native to all of the world’s oceans. There are about 1,800 different species of starfish with the greatest variety living in the tropical Indo-Pacific region. Most starfish have five arms, although some have fewer or more arms. Like other enchinoderms, starfish have small tube feet on their underneath body to help with movement and feeding. The starfish’s mouth is underneath, and it has two stomachs in the mouth. The stomach sack can come out through the mouth to engulf and digest food, such as clams and mussels. Starfish are capable of both sexual and asexual reproduction (by fragmentation or fertilization).


Crustaceans are a type of Arthropod. The name may not sound familiar, but you probably know them. You may even have eaten one.

Crustaceans live mostly in the ocean or other waters. Most commonly known crustaceans are the crab, lobster and barnacle.

Crustaceans have a hard, external shell which protects their body. Crustaceans have a head and abdomen. The head has antennae which are part of their sensory system. The abdomen includes the heart, digestive system and reproductive system. The abdomen also has appendages, such as legs, for crawling and swimming. Many crustaceans also have claws that help with crawling and eating.

-Here you will find fantastic videos about crustaceans:

There are about 10,000 different species of crab. The crab is native to all of the world’s oceans. There are also freshwater crabs, and even some crabs that live on land. Crabs have a large, hard shell. Extending from the front of its shell are the eyes, mouth and two pairs of antennae. The crab has 5 pairs of legs extending from the side of its shell. The first pair of legs have claws or pincers used to catch and hold food. The other pairs of legs are used for walking. Most crabs don’t swim, they use their legs to walk. However, some crabs such as the Blue Crab can use their legs as paddles to swim.

Krill are small crustaceans native to all oceans of the world. Krill are small shrimp-like creatures usually 1/4 inch to 2 inches in length. Krill are considered near the bottom of the food chain. They eat phytoplankton, single-celled plants that float in the seas near the surface. Krill then become food for fish and other animals that can’t eat plants. They are an important food for sea creatures such as baleen whales, manta rays, whale sharks, crabeater seals, and a some seabirds. Most krill travel in large swarms with as many as 10,000 to 60,000 krill per cubic meter. These dense swarms elicit a feeding frenzy among fish, birds and mammal predators.

Lobsters are native to most oceans of the world. The lobster habitat is rocky, sandy or muddy ocean bottom and they are generally found hiding in crevices or in burrows under rocks. Lobsters have five pairs of legs, the first pair of legs are claws used to catch and hold food. Lobsters have a large exoskeleton. As lobsters grow, the must molt to shed their old exoskeleton as they grow a larger new shell.

Shrimp are native to many of the world’s oceans and lakes. They are generally found in shallow water. Their habitat includes both fresh and salt water. Although most shrimp are small, some can grow up to 9 inches in length. The shrimp has a very simple body consisting of the head and thorax, and a muscular abdomin for swimming. They have 8 pairs of legs, 5 for swimming and 3 for feeding. They also have 2 pairs of antennae use for taste and smell to find food. As a crustacean, the shrimp has a thin, almost transparent, exoskeleton. The shrimp is a popular food. In addition to commercial fishing for shrimp, shrimp are also grown in shrimp farms. Shrimp are also commonly found in aquariums.


Arachnids are a type of arthropod. You know many of them as spiders. Common arachnids are spiders, scorpions, ticks and mites.

Like other arthropods, the arachnids have a hard exoskeleton and jointed appendages for walking. Most arachnids have 4 pairs of legs. In some, the first pair of legs may be used for holding their prey and feeding. Unlike other arthropods, arachnids do not have antennae. Spiders are easily recognized with their 8 legs. All legs are used for walking. The first pair of legs is also used for holding prey and feeding. The second pair of legs may also be used for holding and killing their prey. Most spiders have 8 eyes. Spiders have fangs that are used to inject poison to paralyze or kill their prey. Many spiders can produce silk threads to spin webs for catching prey, and for building an egg sack to hold and protect their eggs.

Scorpions are large arachnids, some reaching over 8 inches in length. They have 4 pairs of legs, and a pair of pincers for catching and holding their prey. Scorpions also have a sharp stinger at the end of their tail that is used to paralyze or kill insects and small animals.

Mites and ticks are small arachnids that are parasites living on the blood and tissue fluid of other animals. They can occasionally transmit disease.

-Now, enjoy the enormous collection of videos about arachnids!:

The baboon spider is an old-world tarantula native to Africa. There are about 42 different species of baboon spider in Africa. Their habitat includes savanna woodlands, grasslands and dry scrublands. They are ground-dwelling spiders, living in silk-lined burrows dug in the ground, or under rocks and stones. Like other tarantulas, they are large, hairy spider ranging in size up to about 3-1/2 inches. Their color is generally varying amounts of brown, yellow, gray and black. They have black pads at the end of their legs. It is a venomous spider, but is not considered dangerous to humans. They have large fangs, but will only bite to subdue prey or in self defense. Some baboon spiders will make a hissing noise when they are agitated. These spiders mostly hunt at night. They feed on insects, other spiders, or small reptiles and amphibians. They will wait for prey to come near the entrance of their burrow. They will then pounce on the prey, and take it back to the burrow to eat.

The black widow is a common name for a variety of different spiders. there are about 31 different species of black widow found throughout the world including North, Central and South America, Europe, Africa, middle East, Asia, Australia and New Zealand. The black widow are venomous spiders, the female black widow being particularly dangerous and possibly deadly to humans. Like all arachnids, the black widow has eight legs and an external exoskeleton. In the United States, the southern, western and northern black widow spiders have an easily recognizable red hourglass figure on their back. The black widow spider spins a silk web to catch insects and other prey, and to protect its egg sack. The black widows silk strand is very strong, even stronger than a similar size strand of steel.

The Brazilian Wandering Spider is native to tropical Central and South America. They are a medium to large spider, measuring up to a 5 inch leg span. It is considered a very aggressive spider, and its venom can be quite lethal. The Guinness World Records 2007 identified the Brazilian Wandering Spider as the most venomous spider in the world. This spider is considered responsible for the most human deaths by spider bite. It will wander into homes and hide in shoes, hats and other clothing. It will then bite the unsuspecting person putting on the clothing. The Brazilian Wandering Spider gets it name because it doesn’t build a web or hide in a burrow to catch its prey. This spider wanders the jungle floor at night in search of prey. The Brazilian Wandering Spider is often called a “Banana Spider” because it will occasionally appear in shipments of bananas heading for the United States and other countries.

Brown recluse spider is native to the United States from the southern Midwest south to the Gulf of Mexico. It is also known as the fiddleback spider because of the violin-shaped marking on its back. Like all arachnids, the brown recluse has eight legs and an external exoskeleton. While most spiders have eight eyes, recluse spiders have six eyes arranged in pairs. Recluse spiders get their name because they generally build their webs in undisturbed places such as woodpiles, sheds, closets, garages and cellars. Although the brown recluse spider is not aggressive, its bite can be very dangerous, and even lethal to small children. Human bites are often the result of the brown recluse hiding in shoes, dressers, bed sheets or clothes.

Daddy-long-legs spiders are native to most countries of the world. They are also commonly known as cellar spiders. The daddy long legs has a small, slender body compared to most spiders. As its name implies, it also has very long legs for the size of its body. These spiders are commonly found in basements of homes and in garages. They are a venomous spider, but the venom is not dangerous to humans. The daddy long legs spins an irregular shaped web to trap its prey. The web isn’t sticky, so the daddy long legs must quickly run out to wrap the insect caught in the web with silk, and then bite it injecting toxin, to prevent the insect from escaping.

There are at least two different families of spiders called funnel web spiders. One family consists of spiders such as the Hobo Spider that can be found in the northwestern United States, western Canada, and western Europe. The other family consists of spiders such as the Sydney Funnel Web Spider. Limited to the Sydney, Australia area, the Sydney Funnel Web is one of the most dangerous spiders in the world. What these spiders have in common is their funnel-shaped web.

The gladiator spider is native to eastern Australian forests. The gladiator has a relatively long and thin body for a spider, and long legs for the size of its body. The gladiator spider is also called the net casting spider because of the way it catches prey. It spins a small web that it holds between two pairs of legs. It then holds the web, or net, a few inches above the ground. The spider waits until an insect wanders below where it is holding the net. The gladiator then drops on top of the insect catching it in the net.

The goliath birdeater is a member of the tarantula family of spiders. They are native to rain forests of northern South America. They are considered to be the largest spider in the world, with a leg span of 12 inches. These spiders mostly live in burrows they dig in the ground, or abandoned burrows dug by other animals. Despite their name, the goliath birdeaters mostly eat insects. They will occasionally eat small mammals, rodents, reptiles or birds that come too close to their burrow. They got their name from early explorers that saw the spider eating a hummingbird.

There are over 6,400 species of harvestmen throughout the world. Most species live in tropical areas such as Southeast Asia and South America. They prefer a humid habitat such as in forests, caves, under rocks and in vegetation. Although the harvestmen looks like a spider, and is an arachnid related to the spider, it is not a spider. The difference between a harvestmen and a spider is that the harvestmen’s two body parts, the abdomen and cephalothorax, are joined together appearing as one body part. Harvestmen have very long, slender legs compared to their body size. They are often called a daddy long legs, but there are two other species of spider also called daddy long legs. The harvestmen spider has been around for a long time, with fossils dating to over 400 million years old.

The hobo spider is a type of funnel web spider native to parts of northwestern United States, western Canada, and western Europe. The hobo spider is sometimes confused with the brown recluse spider due to similar coloring. The hobo spider is brown with a chevron or herringbone pattern on the top side of its abdomen. It has smooth, light brown colored legs. As with other funnel web spiders, the hobo spider builds a funnel-shaped web and lies at the small end of the funnel waiting for insects to get caught in the web. Hobo spiders are considered aggressive, and their bite can cause considerable pain in a human.

There are over 5,000 species of jumping spiders throughout the world. Most live in tropical forests, although many species live in temperate forests, scrub lands, deserts, intertidal zones, and even mountains. There are a few hundred species of jumping spiders in the United States and Canada. Jumping spiders are often very colorful. Their bright colors help to attract a mate. Jumping spiders have excellent vision with four big eyes on the face and four smaller eyes on top of the head. The jumping spider’s name comes from the ability to jump over 50 times its body length. To do this, the jumping spider doesn’t have strong jumping legs like a grasshopper. It uses muscle contractions forcing body fluid into the legs, quickly extending the legs resulting in a jump. Before jumping the spider anchors a strand of web so that if it falls the spider can climb back up the thread. The jumping spider hunts during the day. It doesn’t rely on a web to catch prey. The jumping spider will stalk its prey by crawling slowly forward, then pouncing on it.

There are over 45,000 species of mites throughout the world. They are closely related to the tick. Mites live in a variety of habitats including soil, water, plants and animals. Most mites are very small, only about 1 mm in size. Interestingly, while larval mites have three pairs of legs, adult mites have four pairs of legs. Many species of mites are considered parasites. They destroy plants and spread disease in animals. One very common mite is the dust mite. Dust mites can be found in mattresses, pillows, upholstered furniture, rugs and other places where people sleep or sit. Dust mites are a major source of allergies in humans, including hay fever, asthma and eczema.

The nursery web spiders are found in many parts of the world. Their habitat includes woodlands or grassland areas with tall grass. The nursery web spider is yellowish-brown in color with a light to dark brown band down the middle of its back, and a slender and tapering abdomen. It looks somewhat like a wolf spider, except with a different arrangement of its eyes. The name nursery web spider comes from the way the female takes care of its eggs. Nursery web spiders don’t build their web to catch prey. They chase down their prey. The nursery web spider builds its web as a nest or nursery for its eggs. The female spider carries her egg sac in her mouthparts until the spiderlings are almost ready to hatch. The mother spider will then build a web or nursery around her egg sac. As they hatch, she will stand guard over the spiderlings until they are old enough to leave the nest.

 The orb weaver is a common spider found in gardens, fields and forests. It is sometimes called a “garden spider.” The orb weaver gets its name from the spiral, wheel-shaped construction of its web. Orb weavers will use weeds, fences, trees, walls, or other structures to build their webs. Their webs are quite intricate, and it can be very interesting to watch an orb weaver build a web. Their webs tend to look very organized compared to many other spiders. Once complete, you will often see the orb weaver sitting in the center of its large web. Many orb weavers will eat their web and build a new one every day. This keeps the web clean and strong. Orb weavers are considered beneficial to humans because they eat flies, mosquitoes, ants, and other insects considered pests.

 The redback spider is native to Australia, and is related to the black widow spider of North American and other parts of the world. The female redback spider is easily recognizable by its black body with a red stripe on its upper abdomen, and “hourglass” shaped red/orange spot on the underside of its abdomen. The male spider is light brown in color and its markings are less distinct than the female. The redback spider builds a irregular or untidy web. They are usually found under rocks, logs, shrubs, bricks, and junk-piles, and in sheds or outdoor toilets. However, they can be found in houses. The redback spider’s venom can cause serious pain in humans, and can be even be deadly to infants and the elderly. Redback Spiders rarely leave their webs, so human bites are usually the result of coming too close to their web. Some bites do occur where the spider has crawled into shoes or clothing.

Scorpions are native to many parts of the world. There are about 1,400 different species of scorpion. They prefer warm or hot climates, but can even be found in cold, snowy areas. Their habitat includes deserts, grasslands and savannahs, forests, intertidal zones, mountains and caves. Scorpions are best known for their long, segmented tail with its venom-injecting barb. The scorpion will use its venomous stinger to capture prey and defend against predators. Scorpions have four pairs of legs and a pair of pincer-like pedipalps. These pincers can also be used to catch prey and defend against predators. Scorpions are nocturnal animals. They prefer to find shelter during the day in underground holes or under rocks where it is cool. They come out at night to hunt and feed. Most scorpions prey on insects, spiders, centipedes, and other scorpions. Large scorpions may also prey on small lizards, snakes and mice.

Tailless whip scorpion, also called the whip spider, is native to tropical and subtropical areas of the world. Despite either of its names, it is not a scorpion or a spider. Unlike true scorpions, the tailless whip scorpion doesn’t have a tail. It is also different from the whip scorpion, that has a whip-like tail. Like other arachnid, the tailless whip scorpion has eight legs. The first pair of legs, however, act as sensory organs. It only uses six legs for walking. The sensory legs are long and thin, extending several times the length of body. The tailless whip scorpion holds one of these legs out in front as it walks, and uses the other to explore to the side. The tailless whip scorpion will dig an underground burrow or live under logs, bark, rocks, leaves and other natural debris. Most are nocturnal and hunt at night. They don’t have silk glands or venomous fangs. They have pincer-like pedipalps for catching and holding prey.

The tarantula is a large, hairy spider found in tropical to temperate regions of the southwestern United States, Mexico, Central America, South America, southern Europe, Asia, Africa and Australia. Tarantulas can go up to 4 inches in body size, and have a leg span of up to 12 inches.

Like other arachnids, the tarantula has eight legs, arranged in four pairs. It also has another pair of appendages used for feeling and gripping prey. The tarantula has two fangs used to inject venom into its prey, or in defense against predators. Tarantulas prefer to hunt at night. They will lay a web, but not to catch their prey. They lay strands of web on the ground to act as a trip wire. When an insect, frog, toad or mouse steps on the strand, alerting the tarantula, it will pounce on the unsuspecting victim.

Although many people find the tarantula scary, it is generally harmless to humans. They will not bite unless provoked, and if bitten the pain is usually similar to that of a bee sting. Some tarantulas have even become a popular pet.

Ticks are small parasites that live on the blood of mammals, birds, and occasionally reptiles and amphibians. They are often found in tall grass and shrubs, where they will wait to attach to a passing animal. Like other arachnids, ticks have eight legs. They do not jump or fly, so they must have physical contact to attach to an animal. Once attached, the tick inserts its mandibles and feeding tube into the skin. They will then feed on the blood of their host animal. Ticks are known to carry a variety of diseases, such as lyme disease. Lyme disease can cause serious health problems for humans, animals and pets.

The trapdoor spider is native to the southern United States, Mexico and parts of Central America. Species can also be found in Europe, Asia, South Africa and Australia. They are large, hairy spiders that nest underground. The trapdoor spider will dig a burrow in the earth and line it with silk. They will cover the entrance of the burrow with a trapdoor made of earth and silk. The trapdoor is hinged on one side with silk so it can open and close. This makes the burrow difficult to see when the trapdoor is closed. Hidden behind the trapdoor, the trapdoor spider can quickly sneak out and catch prey, such as insects, that wander to close to its burrow.

Whip scorpions are native to tropical and subtropical areas of the world. Although the whip scorpion looks somewhat like a scorpion, it is not a true scorpion. The whip scorpion does not have a stinger. Instead it has a whip-like tail. There are also tailless whip scorpions which are a different family of arachnid. Like other arachnids, the whip spider has eight legs. However, the first pair of legs are adapted as sensory organs. They only use six legs for walking. They also have large, scorpion-like pincers use to catch and hold prey. The whip scorpion will dig an underground burrow or live under logs, rotting wood, rocks, and other natural debris. They hunt at night to feed on insects and millipedes.

There are a variety of different species of wolf spider. They can be found in habitats such as forests, meadows, and even suburban gardens. Wolf Spiders are large, hairy spiders usually black, gray and brown in color. Wolf spiders have two body parts with eight legs, eight eyes and fang-like mouthparts. Though wolf spiders are usually harmless to humans, their venomous bite can cause swelling, mild pain and itching. Wolf spiders do not use webs to capture prey. They stalk, chase and pounce on their prey like a wolf. Unlike other spiders that attach their egg-sack to their web, the female wolf spider carries its egg sac on her abdomen until the spiderlings hatch.


Insects are the largest group of arthropods. There are over 800,000 different types of insects. Insects are very adaptable, living almost everywhere in the world. Common insects include the fly, beetle, butterfly, moth, dragonfly, bee, wasp and praying mantis.

Insects have an exoskeleton that covers their entire body. An insect’s body consists of 3 parts: the head, thorax and abdomen.

The insect’s head has a pair of antennae, and a pair of compound eyes. Compound eyes are different from human eyes which have a single lens for each eye. Compound eyes have many lenses for each eye. For example, the fly has about 4,000 lenses in a single eye. This provides them with very good eyesight. The thorax contains the legs for walking, swimming, jumping or digging. The thorax may also have wings for flying. The abdomen contains many body organs, such as the heart, respiratory system, digestive system and reproductive system.

The insect’s hard, exoskeleton makes it difficult for the insect to grow and get larger. This is because the exoskeleton can’t grow and get larger. Many insects must molt in order to grow. Molting is the process where an insect sheds it outer skeleton. It wriggles out of this old skin, and a new, larger exoskeleton develops.

Learn about insects with an ant’s explanation and pictures.


Cnidarians are marine invertebrates. Many cnidarian species exist in two different body forms during their life cycle: the free-swimming form, called the medusa (a jellyfish for instance), and the stationary form called the polyp (which resembles a tiny sea anemone).

Both forms have a single opening that serves as the mouth and anus and is typically surrounded by a ring of tentacles packed with stinging cells called cnidocytes.

Cnidarians have a defined top and bottom and are made up of two layers of tissue that include nerve and muscle cells. This body, formed from tissues with organized groupings of muscles and nerves, allowed ancestral cnidarians to be the first animals on the planet to show animated behavior.

-Now, enjoy the following videos about cnidarians!

Coral are marine animals found in tropical ocean areas. They are best known for building large coral reefs. Like other cnidarians, a coral is not a single organism, but made up of thousands of small polyps. Each polyp measuring only a few millimeters in diameter. Coral catch and feed on organisms, such as small fish and plankton, using stinging cells on their tentacles. Reefs are formed over thousands of years from coral skeletons held together by layers of calcium carbonate produced by the coral. It takes a lot of polyps to form a reef, but over time reefs can grow very large. The Great Barrier Reef, after 500,000 years, is so large that it can be seen from outer space. It is the world’s biggest single structure made by living organisms.

There are about 1,500 species of jellyfish and they are found in all oceans of the world. They can also be found at every depth, from floating near the surface to the deepest depths of the ocean. Despite their name, jellyfish are not fish. They are actually a cnidarian. They are called jellyfish because they feel like jelly when touched. Jellyfish look at lot like an umbrella floating under the surface of the water. Jellyfish do not have a brain, heart or blood, but they still manage to live, eat and swim like other marine animals. They move forward by expanding and contracting their bell-shaped body. Jellyfish tend to travel in large groups or swarms carried by the ocean currents. Some jellyfish have a green fluorescent protein that causes them to glow in the water. Some jellyfish tentacles have a toxin capable of stinging and even killing its prey.

There are over 1,000 different species of sea anemone found in most oceans of the world. Sea anemones live at various depths, although most are found in coastal tropical waters. The sea anemone is named after the anemone land-growing flower. Although the sea anemone looks like a flower, it is actually an animal. It has a cylindrical body with tentacles surrounding its central mouth. These tentacles are capable of injecting a paralyzing neurotoxin into its prey. The sea anemone attaches itself to rocks on the sea bottom or to coral reefs. It then waits for fish to pass by catching them with their venom-filled tentacles. The sea anemone has developed an interesting relationship with the clownfish. Clownfish are immune to the stinging tentacles. The sea anemone protects the clownfish from predators. In exchange, the clownfish cleans the sea anemone’s tentacles.

The sea pen is a family of 14 different species of marine cnidarians found in tropical and temperate oceans of the world. They are sometimes called “soft corals” along with sea whips and sea feathers. Sea pens prefer deep waters where they are less likely to be uprooted. Their name comes from the fact they look like an old feather quill pen. Sea pens are made up of several parts called polyps. Each polyp provides a specific function to the organism as a whole. For example, one polyp is the stalk. Another polyp is the feeding structure, while another polyp provides for reproduction.

Siphonophores are a family of marine invertebrates similar to the jellyfish. The best known species is the dangerous Portuguese Man o’ War. Siphonophores are actually not a single animal, but a highly specialized colony of organisms called polyps or zooids. Siphonophores can grow up to 130 feet in length. They prey on small animals using stinging cells. The stinging cells have glowing ends that appear to twinkle and attract small fish.

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