Characteristics of Arthropods There are more than a million different species of arthropods, (AR...
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![Page 1: Characteristics of Arthropods There are more than a million different species of arthropods, (AR thruh pahdz). The jointed appendages of arthropods can.](https://reader035.fdocuments.in/reader035/viewer/2022062802/56649ea25503460f94ba662f/html5/thumbnails/1.jpg)
Characteristics of Arthropods
• There are more than a million different species of arthropods, (AR thruh pahdz).
• The jointed appendages of arthropods can include legs, antennae, claws, and pincers.
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• Arthropods also have bilateral symmetry, segmented bodies, an exoskeleton, a body cavity, a digestive system with two openings, and a nervous system.
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Characteristics of Arthropods
• Most arthropods species have separate sexes and reproduce sexually.
• Arthropods are adapted to living in almost every environment.
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Segmented Bodies
• The bodies of arthropods are divided into segments.
• Some arthropods have many segments, but others have segments that are fused together to form body regions, such as those of insects, spiders, and crabs.
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Exoskeletons
• All arthropods have a hard, outer covering called an exoskeleton.
• It covers, supports, and protects the internal body and provides places for muscles to attach.
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• In many land-dwelling arthropods, such as insects, the exoskeleton has a waxy layer that reduces water loss from the animal.
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Exoskeletons
• An exoskeleton cannot grow as the animal grows.
• From time to time, the exoskeleton is shed and replaced by a new one in a process called molting.
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• While the animals are molting, they are not well protected from predators because the new exoskeleton is soft.
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Insects• More species of insects exist then all other
animal groups combined.• More than 700,000 species of insects have
been classified, and scientists identify more each year.
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• Insects have three body regions—a head, a thorax, and an abdomen.
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Head• An insect’s head has a pair of antennae, eyes,
and a mouth.• The antennae are used for
touch and smell.
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• The eyes are simple or compound. Simple eyes detect light and darkness.
• Compound eyes contain many lenses and can detect colors and movement.
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Thorax• Three pairs of legs and one or two pairs of
wings, if present, are attached to the thorax.• Insects are the only
invertebrate animals that can fly.
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• Flying allows insects to find places to live, food sources, and mates.
• Flight also helps them escape from their predators.
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Abdomen• The abdomen is where the reproductive
structures are found.
• Insects have an open circulatory system that carries digested food to cells and removes wastes.
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• Insects have openings called spiracles (SPIHR ih kulz) on the abdomen and thorax through which air enters and waste gases leave the insect’s body.
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From Egg to Adult
• Grasshoppers, silverfish, lice, and crickets undergo incomplete metamorphosis.
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• Many insects go through changes in body form calledmetamorphosis (me tuh MOR fuh sihs).
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From Egg to Adult• Many insects, like butterflies, beetles, ants,
bees, moths, and flies, undergo complete metamorphosis.
• The stages of complete metamorphosis are egg, larva, pupa, and adult.
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Click box to view movie.
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Obtaining Food• Grasshoppers and ants have large mandibles
(MAN duh bulz) for chewing plant tissue.
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• Butterflies and honeybees are equipped with siphons forlapping up nectar in flowers.
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Obtaining Food• Praying mantises eat other
animals.• External parasites, such as
mosquitoes, fleas, and lice, drink the blood and body fluids of other animals.
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• Silverfish eat things that contain starch and some moth larvae eat wool clothing.
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Insect Success
• Most insects have short life spans, so genetic traits can change more quickly in insect populations than in organisms that take longer to reproduce.
• Because insects generally are small, they can live in a wide range of environments and avoid their enemies.
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Insect Success
• Many species of insects can live in the same area and not compete with one another for food, because many are so specialized in what they eat.
• Protective coloration, or camouflage, allows insects to blend in with their surroundings.
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Arachnids• Spiders, scorpions, mites, and ticks are
examples of arachnids (uh RAK nudz).
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• They have two body regions, a head-chest region called the cephalothorax (se fuh luhTHOR aks) and an abdomen.
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Arachnids
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• Arachnids have four pairs of legs but no antennae.
• Many arachnids are adapted to kill prey with venom glands, stingers, or fangs.
• Others are parasites.
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Scorpions• Arachnids that have a sharp, venom-filled
stinger at the end of their abdomen are called scorpions.
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• Unlike other arachnids, scorpions have a pair of well-developed appendages, pincers, with which they grab their prey.
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Spiders
• Because spiders can’t chew their food, they release enzymes into their prey that help digest it, then they suck it back into their mouth’s.
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Spiders
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• Oxygen and carbon dioxide are exchanged in book lungs.
• Openings on the abdomen allow these gases to move into and out of the book lungs.
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Mites and Ticks• Most mites are animal or plant parasites,
like the mites that live in the follicles of human eyelashes.
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• Most mites are so small that they look like tiny specs to the unaided eye.
• Ticks attach to their host’s skin and remove blood through specialized mouthparts.
• Diseases carried by ticks include Lyme disease and Rocky Mountain spotted fever.
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Centipedes and Millipedes• Two groups of arthropods, centipedes
and millipedes, have long bodies with many segments and many legs, antennae, and simple eyes.
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• They can be found in damp environments, including in woodpiles, under vegetation, and in basements.
• Centipedes and millipedes reproduce sexually. They make nests for their eggs and stay with them until the eggs hatch.
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Centipedes and Millipedes• Centipedes hunt for their prey, which
includes snails, slugs, and worms.
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• They have a pair of venomous claws that they use to inject venom into their prey.
• Millipedes feed on plants and decaying material and often are found under damp plant material.
Click image to view movie.
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Crustaceans• Crabs, crayfish,
shrimp, barnacles, pill bugs, and water fleas are crustaceans.
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• Most crustaceans live in water, but some live in moist environments on land.
• Crustaceans haveone or two pairs of antennae and mandibles, which are used for crushing food.
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Crustaceans• Crustaceans have five pairs of legs.
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• The first pair of legs are claws that catch and hold food.
• The other four pairs are walking legs.
• They also have five pairs of appendages on the abdomen called swimmerets.
• If a crustacean loses an appendage, it will grow back, or regenerate.
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Value of Arthropods• Arthropods are a source of food for many
animals, including humans.
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• Bees, butterflies, moths, and flies pollinate crops.
• Bees manufacture honey, and silkworms produce silk.
• Many insects and spiders are predators of harmful animal species.
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Value of Arthropods• Not all arthropods are useful to humans.
Almost every cultivated crop has some insect pest that feeds on it.
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• Many arthropods, including mosquitoes, tsetse flies, fleas, and ticks, carry human and other animal diseases.
• In addition, weevils, cockroaches, carpenter ants, clothes moths, termites, and carpet beetles destroy food, clothing, and property.
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Controlling Insects
• One common way to control problem insects is by insecticides.
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• However, many insecticides also kill helpful insects.
• Another problem is that many toxic substances that kill insects remain in the environment and accumulate in the bodies of animals that eat them.
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Controlling Insects
• Different types of bacteria, fungi, and viruses are being used to control some insect pests.
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• Other biological controls include using sterile males or naturally occurring chemicals that interfere with the reproduction or behavior of insect pests.
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Origin of Arthropods• Because of their hard body parts, arthropod
fossils are among the oldest and best-preserved fossils of many-celled animals.
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• Scientists hypothesize that arthropods probably evolved from an ancestor of segmented worms.