Echinoderm, pronounced ih KY nuh durm, is the general name of certain spiny-skinned sea animals. There are about 6,000 kinds of echinoderms. Starfish, brittle stars, sand dollars, sea urchins, and sea cucumbers are among the most common kinds. All echinoderms have an internal bony skeleton. Their spines are a part of the skeleton. The echinoderm phylum (large animal group) is the only major phylum made up entirely of sea animals.
Adult echinoderms have radial symmetry. Their body parts are arranged around the center of the animal like the spokes of a wheel around the hub. Echinoderm bodies are usually divided into five sections with the mouth in the center.
Echinoderms are the only animals that have many tiny tubelike structures called tube feet. The tube feet project from the body in rows. Echinoderms use the tube feet for moving, feeding, breathing, and sensing. The outer tip of each tube often forms a suction disk for gripping hard surfaces. Within the echinoderm's body, a tiny bulb attached to the tube foot forces water into it to make it lengthen. An internal system of water-filled canals connects the tube feet to each other and to a sievelike plate that usually opens to the sea water. The entire system of tube feet and canals is called the water vascular system.
Echinoderms reproduce by laying eggs that develop into larvae and swim freely. The larvae have bilateral symmetry (two similar halves). The larvae sink to the ocean bottom and change into the adult, radial form.
Scientific classification. Echinoderms make up the echinoderm phylum, Echinodermata.
Wednesday, February 21, 2007
Mollusks
Mollusk, pronounced MAHL uhsk, is a soft-bodied animal that has no bones. Snails, slugs, clams, mussels, oysters, squids, and octopuses are mollusks. Most mollusks have a hard shell that protects their soft bodies. Some, such as cuttlefish and squids, have no outside shell. A special shell grows inside their bodies. This shell is called a cuttlebone in cuttlefish and a pen in squids. A few kinds of mollusks, including octopuses and certain slugs, have no shell at all. For additional information on mollusk shells and how they are formed.
All mollusks have a skinlike organ called the mantle. In mollusks with outside shells, the mantle makes the shell. The edges of the mantle release liquid shell materials and add them to the shell as the mollusk grows. In mollusks with no outside shell, the mantle forms a tough cover around the body organs.
Mollusks live in most parts of the world. Some kinds of mollusks live in the deepest parts of oceans. Others are found on the wooded slopes of high mountains. Still others live in hot, dry deserts. Wherever mollusks live, they must keep their bodies moist to stay alive. Most land mollusks live in damp places such as under leaves or in soil.
Mollusks are used mainly for food. People in many parts of the world eat mollusks every day. Most Americans do not eat them nearly so often. The most popular kinds used as food in the United States are clams, oysters, and scallops. Mollusk shells are made into many useful products, including pearl buttons, jewelry, and various souvenir items. Perhaps the best-known mollusk products are the pearls made by pearl oysters.
Some mollusks are harmful to people. For example, certain small, freshwater snails of the tropics carry worms that cause an often fatal disease called schistosomiasis. Shipworm clams drill into rope, wooden boats, and wharves and cause millions of dollars worth of damage a year.
Mollusks make up the largest group of water animals. There are about 50,000 known kinds of living mollusks, and scientists find about 1,000 new species every year. The fossils of about 100,000 other species of mollusks have also been found.
The mollusks make up a phylum (major division) of the animal kingdom. The scientific name of the phylum is Mollusca, a Latin word meaning soft-bodied. To learn where the phylum fits into the animal kingdom, see ANIMAL.
There are seven classes (large groups) of mollusks. They are (1) univalves or Gastropoda, (2) bivalves or Bivalvia or Pelecypoda, (3) octopuses and squids or Cephalopoda, (4) tooth shells or Scaphopoda, (5) chitons or Polyplacophora, (6) Monoplacophora, and (7) Aplacophora.
Univalves or gastropods (Gastropoda) are the largest class of mollusks. They include limpets, slugs, snails, and whelks. Most kinds of univalves have a single, coiled shell. The name univalve comes from Latin words meaning one shell. But some kinds of univalves, including garden slugs and the sea slugs called nudibranchs, have no shells after the larval stage.
The name Gastropoda comes from Greek words meaning belly and foot. Gastropods seem to crawl on their bellies, but actually they use a large, muscular foot. The foot spreads beneath the body, and its muscles move in a rippling motion that makes the animal move forward. Most sea snails and some land snails have a lidlike part called an operculum on the back of the foot. When danger threatens, the snail draws back into its shell and the operculum closes the shell opening.
Certain kinds of univalves have two pairs of tentacles (feelers) on their heads. One pair helps the animals feel their way about. Some species have an eye on each of the other two tentacles. Others have no eyes at all. A univalve also has a ribbon of teeth. This ribbon, called a radula, works like a rough file and tears apart the animal's food. Most univalves that eat plants have thousands of weak teeth. A few kinds eat other mollusks, and have several dozen strong teeth.
Bivalves (Bivalvia or Pelecypoda) form the second largest class of mollusks. They include clams, oysters, mussels, scallops, and shipworms. All bivalves have two shells held together by hinges that look like small teeth. The shells of bivalves are usually open. When the animals are frightened, strong muscles pull the shells shut and hold them closed until danger has passed.
Bivalves have a strong, muscular foot. Many kinds of these animals move about by pushing the foot out and hooking it in the mud or sand. Then they pull themselves up with the foot. Some bivalves, such as the geoduck and razor clam, use the foot to dig holes. They push the foot downward into mud or sand. First the foot swells to enlarge the hole, and then it contracts and pulls the shell into the burrow. The Pholas clam can dig holes even in hard clay or soft rock.
Bivalves have no head or teeth. They get oxygen and food through a muscular siphon (tube). The siphon can be stretched to reach food and water if the animal is buried in mud or sand. Bivalves feed on plant cells material, which is filtered from the water by the gills.
Octopuses and squids (Cephalopoda) are the most active mollusks. The argonaut, cuttlefish, and nautilus also belong to this group. All the species in the group live in the ocean.
The word Cephalopoda comes from Greek words meaning head and foot. A cephalopod seems to be made up of a large head and long arms that look like feet. Octopuses and squids have dome-shaped "heads" surrounded by arms. Octopuses have eight arms, and squids have eight arms and two tentacles. The arms grow around hard, strong, beaklike jaws on the underside of the head. These jaws tear the animal's prey, and are far more dangerous than the arms. Octopuses use their arms and squids use their tentacles and arms to capture prey and pull it through their jaws. Octopuses and squids eat fish, other mollusks, and shellfish.
Tooth shells (Scaphopoda) have slender, curving shells that resemble tusks. These mollusks are often called tusk shells. The word Scaphopoda comes from Greek words that mean boat and foot. A tooth shell has a pointed foot that looks somewhat like a small boat. All tooth shells live in the ocean, where they burrow in the mud or sand. The top of the shell sticks up into the water. Tooth shells have no head or eyes. They feed on one-celled organisms that are swept into the mouth by tentacles.
Chitons (Polyplacophora) have flat, oval bodies covered by eight shell plates. The plates are held together by a tough girdle. The name Polyplacophora comes from Greek words that mean many, shell, and bearer. This name refers to the eight overlapping pieces of a chiton's shell. Chitons have a large, flat foot. They can use the foot to move about, but they usually cling firmly to rocks. When they are forced to let go of the rocks, they roll up into a ball. Chitons have a small head and mouth, but they have no eyes or tentacles. Their long radula has many teeth, which some chitons use to scrape seaweed from rocks for food.
Monoplacophora live in the deep parts of the ocean, and most are found only as fossils. The name Monoplacophora comes from Greek words meaning single, shell, and bearer. Monoplacophorans have one shell that is almost flat, like a limpet shell. They are unusual because they have several pairs of gills, six or more pairs of kidneys, and many ladderlike nerve centers. Like other mollusks, they have a mantle. They also have a radula. Little is known about their habits.
Aplacophora are rarely seen, wormlike mollusks covered with small spines. The name Aplacophora comes from Greek words that mean no shell.
All mollusks have a skinlike organ called the mantle. In mollusks with outside shells, the mantle makes the shell. The edges of the mantle release liquid shell materials and add them to the shell as the mollusk grows. In mollusks with no outside shell, the mantle forms a tough cover around the body organs.
Mollusks live in most parts of the world. Some kinds of mollusks live in the deepest parts of oceans. Others are found on the wooded slopes of high mountains. Still others live in hot, dry deserts. Wherever mollusks live, they must keep their bodies moist to stay alive. Most land mollusks live in damp places such as under leaves or in soil.
The importance of mollusks
Mollusks are used mainly for food. People in many parts of the world eat mollusks every day. Most Americans do not eat them nearly so often. The most popular kinds used as food in the United States are clams, oysters, and scallops. Mollusk shells are made into many useful products, including pearl buttons, jewelry, and various souvenir items. Perhaps the best-known mollusk products are the pearls made by pearl oysters.
Some mollusks are harmful to people. For example, certain small, freshwater snails of the tropics carry worms that cause an often fatal disease called schistosomiasis. Shipworm clams drill into rope, wooden boats, and wharves and cause millions of dollars worth of damage a year.
Kinds of mollusks
Mollusks make up the largest group of water animals. There are about 50,000 known kinds of living mollusks, and scientists find about 1,000 new species every year. The fossils of about 100,000 other species of mollusks have also been found.
The mollusks make up a phylum (major division) of the animal kingdom. The scientific name of the phylum is Mollusca, a Latin word meaning soft-bodied. To learn where the phylum fits into the animal kingdom, see ANIMAL.
There are seven classes (large groups) of mollusks. They are (1) univalves or Gastropoda, (2) bivalves or Bivalvia or Pelecypoda, (3) octopuses and squids or Cephalopoda, (4) tooth shells or Scaphopoda, (5) chitons or Polyplacophora, (6) Monoplacophora, and (7) Aplacophora.
Univalves or gastropods (Gastropoda) are the largest class of mollusks. They include limpets, slugs, snails, and whelks. Most kinds of univalves have a single, coiled shell. The name univalve comes from Latin words meaning one shell. But some kinds of univalves, including garden slugs and the sea slugs called nudibranchs, have no shells after the larval stage.
The name Gastropoda comes from Greek words meaning belly and foot. Gastropods seem to crawl on their bellies, but actually they use a large, muscular foot. The foot spreads beneath the body, and its muscles move in a rippling motion that makes the animal move forward. Most sea snails and some land snails have a lidlike part called an operculum on the back of the foot. When danger threatens, the snail draws back into its shell and the operculum closes the shell opening.
Certain kinds of univalves have two pairs of tentacles (feelers) on their heads. One pair helps the animals feel their way about. Some species have an eye on each of the other two tentacles. Others have no eyes at all. A univalve also has a ribbon of teeth. This ribbon, called a radula, works like a rough file and tears apart the animal's food. Most univalves that eat plants have thousands of weak teeth. A few kinds eat other mollusks, and have several dozen strong teeth.
Bivalves (Bivalvia or Pelecypoda) form the second largest class of mollusks. They include clams, oysters, mussels, scallops, and shipworms. All bivalves have two shells held together by hinges that look like small teeth. The shells of bivalves are usually open. When the animals are frightened, strong muscles pull the shells shut and hold them closed until danger has passed.
Bivalves have a strong, muscular foot. Many kinds of these animals move about by pushing the foot out and hooking it in the mud or sand. Then they pull themselves up with the foot. Some bivalves, such as the geoduck and razor clam, use the foot to dig holes. They push the foot downward into mud or sand. First the foot swells to enlarge the hole, and then it contracts and pulls the shell into the burrow. The Pholas clam can dig holes even in hard clay or soft rock.
Bivalves have no head or teeth. They get oxygen and food through a muscular siphon (tube). The siphon can be stretched to reach food and water if the animal is buried in mud or sand. Bivalves feed on plant cells material, which is filtered from the water by the gills.
Octopuses and squids (Cephalopoda) are the most active mollusks. The argonaut, cuttlefish, and nautilus also belong to this group. All the species in the group live in the ocean.
The word Cephalopoda comes from Greek words meaning head and foot. A cephalopod seems to be made up of a large head and long arms that look like feet. Octopuses and squids have dome-shaped "heads" surrounded by arms. Octopuses have eight arms, and squids have eight arms and two tentacles. The arms grow around hard, strong, beaklike jaws on the underside of the head. These jaws tear the animal's prey, and are far more dangerous than the arms. Octopuses use their arms and squids use their tentacles and arms to capture prey and pull it through their jaws. Octopuses and squids eat fish, other mollusks, and shellfish.
Tooth shells (Scaphopoda) have slender, curving shells that resemble tusks. These mollusks are often called tusk shells. The word Scaphopoda comes from Greek words that mean boat and foot. A tooth shell has a pointed foot that looks somewhat like a small boat. All tooth shells live in the ocean, where they burrow in the mud or sand. The top of the shell sticks up into the water. Tooth shells have no head or eyes. They feed on one-celled organisms that are swept into the mouth by tentacles.
Chitons (Polyplacophora) have flat, oval bodies covered by eight shell plates. The plates are held together by a tough girdle. The name Polyplacophora comes from Greek words that mean many, shell, and bearer. This name refers to the eight overlapping pieces of a chiton's shell. Chitons have a large, flat foot. They can use the foot to move about, but they usually cling firmly to rocks. When they are forced to let go of the rocks, they roll up into a ball. Chitons have a small head and mouth, but they have no eyes or tentacles. Their long radula has many teeth, which some chitons use to scrape seaweed from rocks for food.
Monoplacophora live in the deep parts of the ocean, and most are found only as fossils. The name Monoplacophora comes from Greek words meaning single, shell, and bearer. Monoplacophorans have one shell that is almost flat, like a limpet shell. They are unusual because they have several pairs of gills, six or more pairs of kidneys, and many ladderlike nerve centers. Like other mollusks, they have a mantle. They also have a radula. Little is known about their habits.
Aplacophora are rarely seen, wormlike mollusks covered with small spines. The name Aplacophora comes from Greek words that mean no shell.
Arthropods
Arthropod, pronounced AHR thruh pahd, is any animal that belongs to the major division, or phylum, of the animal kingdom called the Arthropoda. This term is formed from two Greek words, and means jointed feet. Actually, the legs, rather than the feet, are jointed. All the Arthropoda, or arthropods, have jointed legs. Among the most important groups of arthropods are the following: (1) insects, including cockroaches, beetles, bees, butterflies, and many others; (2) crustaceans, including such well-known animals as crabs, lobsters, shrimps, and barnacles; (3) arachnids, including mites, ticks, spiders, and scorpions; (4) chilopods, or centipedes; and (5) diplo-pods, or millipedes. The arthropod phylum contains more than three-fourths of all the different kinds of animals. Insects make up the largest class of arthropods in terms of the number of species.
The bodies of arthropods, as well as their legs, are made up of sections. Among some primitive arthropods, each section of the body has its own pair of legs. Most of these legs are used for swimming or walking. In some types of arthropods, certain legs have developed special shapes and uses. Some serve as sucking organs, some are jaws, some serve as weapons of offense and defense, and some are sense organs. Insects lack most of the pairs of legs found in other arthropods. They have only three pair. One pair is attached to each segment of an insect's chest or thorax. Insects also may have one or two pairs of wings.
Arthropods have an outside shell, or exoskeleton, that contains a stiff, horny material called chitin. Certain arthropods, such as flies and moths, have only thin, weak shells. Others, including crabs and lobsters, have thick, strong shells. Nearly all arthropods have a kind of heart and blood system and usually a well-organized nervous system. Some arthropods have simple eyes, some have compound eyes, and some (including many insects) have eyes of both types.
The bodies of arthropods, as well as their legs, are made up of sections. Among some primitive arthropods, each section of the body has its own pair of legs. Most of these legs are used for swimming or walking. In some types of arthropods, certain legs have developed special shapes and uses. Some serve as sucking organs, some are jaws, some serve as weapons of offense and defense, and some are sense organs. Insects lack most of the pairs of legs found in other arthropods. They have only three pair. One pair is attached to each segment of an insect's chest or thorax. Insects also may have one or two pairs of wings.
Arthropods have an outside shell, or exoskeleton, that contains a stiff, horny material called chitin. Certain arthropods, such as flies and moths, have only thin, weak shells. Others, including crabs and lobsters, have thick, strong shells. Nearly all arthropods have a kind of heart and blood system and usually a well-organized nervous system. Some arthropods have simple eyes, some have compound eyes, and some (including many insects) have eyes of both types.
Nematodes
Roundworm, also called nematode or eelworm, is any of more than 12,000 species of worms. Many species of roundworms live freely in soil, water, dead plants, or dead animals. All other roundworms are parasites. They live and feed on living plants and animals, which serve as hosts. Some parasitic species cause serious diseases in human beings and other hosts.
Roundworms range in size from microscopic to more than 3 feet (90 centimeters) long. They have slender, round bodies with tapered ends. Roundworms have remarkable powers of reproduction and are extremely numerous. Researchers have found more than 90,000 roundworms in a single rotting apple.
Nearly all species of roundworms reproduce by laying eggs. Some species produce great quantities of eggs. For example, females of the species Ascaris lumbricoides each lay about 200,000 eggs per day for at least 10 months. Among some species of roundworms, the eggs hatch into tiny young that look like the adults. Eggs of other species hatch into young called larvae, which gradually transform into adults. Species of roundworms that do not lay eggs give birth to larvae.
Parasitic roundworms may infect a host in a number of ways. Some species enter the host when the host swallows food that contains the roundworm, its eggs, or its larvae. Among other species, the larva burrows into the skin of the host. In other species of roundworms, the larva is taken up by an insect, such as a fly or a mosquito, and transmitted through the bite of that insect to the host.
At least 14 species of roundworms cause infection in human beings. A. lumbricoides, which inhabits the small intestine, infects about 65 million people throughout the world. It causes a disease called ascariasis. Symptoms of this disease include pneumonia and intestinal pain. The roundworm Trichuris trichiura infects the large intestine and occurs in about 350 million people worldwide. It causes trichuriasis, a disease characterized by diarrhea. Other common roundworms that cause disease in humans include filariae, hookworms, pinworms, and trichinae.
Roundworms range in size from microscopic to more than 3 feet (90 centimeters) long. They have slender, round bodies with tapered ends. Roundworms have remarkable powers of reproduction and are extremely numerous. Researchers have found more than 90,000 roundworms in a single rotting apple.
Nearly all species of roundworms reproduce by laying eggs. Some species produce great quantities of eggs. For example, females of the species Ascaris lumbricoides each lay about 200,000 eggs per day for at least 10 months. Among some species of roundworms, the eggs hatch into tiny young that look like the adults. Eggs of other species hatch into young called larvae, which gradually transform into adults. Species of roundworms that do not lay eggs give birth to larvae.
Parasitic roundworms may infect a host in a number of ways. Some species enter the host when the host swallows food that contains the roundworm, its eggs, or its larvae. Among other species, the larva burrows into the skin of the host. In other species of roundworms, the larva is taken up by an insect, such as a fly or a mosquito, and transmitted through the bite of that insect to the host.
At least 14 species of roundworms cause infection in human beings. A. lumbricoides, which inhabits the small intestine, infects about 65 million people throughout the world. It causes a disease called ascariasis. Symptoms of this disease include pneumonia and intestinal pain. The roundworm Trichuris trichiura infects the large intestine and occurs in about 350 million people worldwide. It causes trichuriasis, a disease characterized by diarrhea. Other common roundworms that cause disease in humans include filariae, hookworms, pinworms, and trichinae.
Rotifers
Rotifer, pronounced ROH tuh fuhr, is a type of tiny multicellular animal that lives in water. The largest rotifers are about 1/26 inch (1 millimeter) long. Rotifers have cylinder- or vase-shaped bodies. Most species live in lakes, rivers, or streams. Some live in the ocean.
The name rotifer means wheel bearer and refers to the circles of hairlike projections called cilia on the animal's head. The cilia create a circular water current that draws food to the rotifer. This water current also enables most species of rotifers to "swim." Other species spend their entire lives attached to such objects as stones and leaves.
In many rotifer populations, the male has no role in reproduction. The female produces young by herself. This kind of reproduction, called parthenogenesis, produces only female offspring.
Scientific classification. Rotifers make up the phylum Rotifera.
The name rotifer means wheel bearer and refers to the circles of hairlike projections called cilia on the animal's head. The cilia create a circular water current that draws food to the rotifer. This water current also enables most species of rotifers to "swim." Other species spend their entire lives attached to such objects as stones and leaves.
In many rotifer populations, the male has no role in reproduction. The female produces young by herself. This kind of reproduction, called parthenogenesis, produces only female offspring.
Scientific classification. Rotifers make up the phylum Rotifera.
Platyhelminthes
Flatworm is a kind of worm. Some flatworms live freely on land or in water. Others live as parasites in human beings or other animals. Many flatworms, especially the larger species, have a flat body.
Flatworms have a simple body structure. A layer of cells called the epidermis covers the animal's body. An inner layer of cells forms an intestine in most flatworms. A tightly packed mass of cells called the parenchyma fills the body between the epidermis and intestine. Muscles, glands, nerves, and reproductive organs lie in the parenchyma. The only opening of the intestine is the animal's mouth. The mouth may be at the head end, the rear end, or the underside of the body.
Many flatworms have a smooth, soft body. Many have suckers or other projections on the body. Some flatworms have spines and tiny, needlelike spicules that serve as a kind of skeleton. Most flatworms measure less than 1 inch (2.5 centimeters) long. However, the largest flatworms, called tapeworms, may grow up to 100 feet (30 meters) long.
There are about 13,000 species of flatworms. They may be divided into four groups: (1) turbellarians; (2) monogeneans; (3) trematodes; and (4) cestodes, or tapeworms. Most turbellarians are free-living. They usually are found in sand and mud on the bottom of bodies of water. A few species live on land in moist soil. The other three groups of flatworms are parasites. They live in a wide variety of organisms that serve as hosts.
Almost all flatworms are hermaphroditic--that is, both male and female reproductive organs are found in the same animal. Most turbellarians lay eggs that hatch into tiny young that resemble the adults. In some turbellarians, and in all parasitic flatworms, young--called larvae--hatch from the eggs. The larvae look different from the adults and live in different habitats. For example, the larva of a monogenean has hairlike cilia that enable it to swim. The larva swims until it finds an appropriate fish for a host. The larva attaches to the fish and develops into an adult. The adult, which lives on the skin and gills of the fish, lacks cilia and cannot swim.
Parasitic flatworms cause disease in their hosts. Schistosomiasis, for example, is a tropical disease caused by schistosomes (blood flukes) living in the blood vessels of the abdomen. Adult tapeworms that live in the intestine of human beings do not usually cause much harm. However, tapeworm larvae cause serious diseases that can be fatal if not treated.
Scientific classification. Flatworms make up the phylum Platyhelminthes. The four classes of flatworms are Turbellaria, Monogenea, Trematoda, and Cestoda.
Flatworms have a simple body structure. A layer of cells called the epidermis covers the animal's body. An inner layer of cells forms an intestine in most flatworms. A tightly packed mass of cells called the parenchyma fills the body between the epidermis and intestine. Muscles, glands, nerves, and reproductive organs lie in the parenchyma. The only opening of the intestine is the animal's mouth. The mouth may be at the head end, the rear end, or the underside of the body.
Many flatworms have a smooth, soft body. Many have suckers or other projections on the body. Some flatworms have spines and tiny, needlelike spicules that serve as a kind of skeleton. Most flatworms measure less than 1 inch (2.5 centimeters) long. However, the largest flatworms, called tapeworms, may grow up to 100 feet (30 meters) long.
There are about 13,000 species of flatworms. They may be divided into four groups: (1) turbellarians; (2) monogeneans; (3) trematodes; and (4) cestodes, or tapeworms. Most turbellarians are free-living. They usually are found in sand and mud on the bottom of bodies of water. A few species live on land in moist soil. The other three groups of flatworms are parasites. They live in a wide variety of organisms that serve as hosts.
Almost all flatworms are hermaphroditic--that is, both male and female reproductive organs are found in the same animal. Most turbellarians lay eggs that hatch into tiny young that resemble the adults. In some turbellarians, and in all parasitic flatworms, young--called larvae--hatch from the eggs. The larvae look different from the adults and live in different habitats. For example, the larva of a monogenean has hairlike cilia that enable it to swim. The larva swims until it finds an appropriate fish for a host. The larva attaches to the fish and develops into an adult. The adult, which lives on the skin and gills of the fish, lacks cilia and cannot swim.
Parasitic flatworms cause disease in their hosts. Schistosomiasis, for example, is a tropical disease caused by schistosomes (blood flukes) living in the blood vessels of the abdomen. Adult tapeworms that live in the intestine of human beings do not usually cause much harm. However, tapeworm larvae cause serious diseases that can be fatal if not treated.
Scientific classification. Flatworms make up the phylum Platyhelminthes. The four classes of flatworms are Turbellaria, Monogenea, Trematoda, and Cestoda.
Annelids
Segmented worms are the most highly developed worms. Their body consists of segments that give the worms a ringed appearance. This group includes polychaete worms, oligochaete worms, and leeches.
Polychaete worms, the largest group of segmented worms, live in the sea and along the shore. Many of these worms have tentacles (feelers) on their head and a pair of leglike projections called parapodia on each body segment. The parapodia are used in crawling. They have many setae (bristles) that help the worms grip the surface on which they are moving. Many polychaete worms live among algae or burrow in mud or sand. Some live in tubes attached to the sea floor. A worm makes its tube from sand or from material secreted by its body. Some polychaete worms eat small plants and animals. Others feed on plant and animal remains.
Oligochaete worms include earthworms and many freshwater species. They have a few setae but no parapodia. Most oligochaete worms eat decaying plant matter.
Leeches make up the smallest group of segmented worms. They grow from 3/8 to 12 inches (1 to 30 centimeters) long and have a flat body with a sucker at each end. Most leeches live in water and feed on the blood of fish and other water creatures.
Polychaete worms, the largest group of segmented worms, live in the sea and along the shore. Many of these worms have tentacles (feelers) on their head and a pair of leglike projections called parapodia on each body segment. The parapodia are used in crawling. They have many setae (bristles) that help the worms grip the surface on which they are moving. Many polychaete worms live among algae or burrow in mud or sand. Some live in tubes attached to the sea floor. A worm makes its tube from sand or from material secreted by its body. Some polychaete worms eat small plants and animals. Others feed on plant and animal remains.
Oligochaete worms include earthworms and many freshwater species. They have a few setae but no parapodia. Most oligochaete worms eat decaying plant matter.
Leeches make up the smallest group of segmented worms. They grow from 3/8 to 12 inches (1 to 30 centimeters) long and have a flat body with a sucker at each end. Most leeches live in water and feed on the blood of fish and other water creatures.
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