13.1 Ecologists Study Relationships
BiologyUnit 25 Arthropods
24.1 Arthropod Diversity
KEY CONCEPT Arthropods are the most diverse of all animals.
24.1 Arthropod Diversity
Arthropod features are highly adapted.
• Arthropods are invertebrates that share several features.– exoskeleton (cuticle) made of chitin– jointed appendages– segmented body parts
24.1 Arthropod Diversity
• Arthropods are classified into five groups.– Trilobites—extinct, bottom feeders
24.1 Arthropod Diversity
– Crustaceans—live in oceans, freshwater streams, and on land
24.1 Arthropod Diversity
– Chelicerates—specialized daggerlike mouthparts
24.1 Arthropod Diversity
– Insects—most live on land, have six legs
24.1 Arthropod Diversity
– Myriapods—long bodies and many pairs of legs
24.1 Arthropod Diversity
Arthropod exoskeletons serve a variety of functions.
• Joints are made of stiff and flexible cuticle to allow movement.
• The exoskeleton is made of many layers of chitin.– hard material that
protects the body– must be shed in order to
grow
24.1 Arthropod Diversity
• Sensory organs such as antennae are made of modified cuticle.
• Most arthropods have compound eyes.
• Arthropods have an open circulatory system.
24.1 Arthropod Diversity
Arthropod diversity evolved over millions of years.
• The oldest fossils are of trilobites that date back 540 million years.
24.1 Arthropod Diversity
– body segmentation similar to annelids– molecular evidence suggests segmentation is
analogous development• Velvet worms and water bears are considered the
closest relatives of arthropods.
• The evolutionary relationship between arthropods and other invertebrates remains under question.
24.1 Arthropod Diversity
KEY CONCEPT Crustaceans are a diverse group of ancient arthropods.
24.1 Arthropod Diversity
Crustaceans evolved as marine arthropods.
– two distinct body sections, cephalothorax and abdomen– one pair of appendages per segment– two pairs of antennae– exoskeleton– carapace
• Crustaceans share several common features.
24.1 Arthropod Diversity
Crustacean appendages can take many forms.
• Crustacean appendages are used for a variety of functions.– collecting and manipulating food– attracting females– protection
24.1 Arthropod Diversity
• Appendages include claws, antennae, walking legs, swimmerets, and mandibles.
24.1 Arthropod Diversity
There are many different types of crustaceans.
• Crustaceans vary in both anatomy and structure.– Decapods such as lobsters and crabs have ten legs.
24.1 Arthropod Diversity
– Barnacles are sessile filter feeders wrapped in a hard shell.
24.1 Arthropod Diversity
– Isopods such as pill bugs have flattened bodies and seven pairs of legs.
– Tongue worms are parasites found in a host’s lungs or nasal passages.
24.1 Arthropod Diversity
KEY CONCEPT Arachnids include spiders and their relatives.
24.1 Arthropod Diversity
Arachnids are the largest group of chelicerates.
• There are three major groups of chelicerates.– horseshoe crabs
24.1 Arthropod Diversity
Arachnids are the largest group of chelicerates.
• There are three major groups of chelicerates.– horseshoe crabs– sea spiders– arachnids
24.1 Arthropod Diversity
poison gland
spinnerets
fangs
– no antennae– four pairs of walking legs– one pair each of chelicerae and pedipalps
• Arachnids are a group of chelicerates that live on land.– eight legs– fanglike pincers
that inject venom– silk glands
• Chelicerates share several features.
24.1 Arthropod Diversity
– waterproof cuticle – book lungs– Malpighian tubules – spiracles
• Arachnids have four different adaptations that reduce water loss.
24.1 Arthropod Diversity
Arachnids have evolved into a diverse group.
• All spiders make silk and produce venom.
24.1 Arthropod Diversity
Arachnids have evolved into a diverse group.
• Spiders make up half of the more than 60,000 known arachnid species.
• Arachnids also include mites, ticks, chiggers, and scorpions.
24.1 Arthropod Diversity
KEY CONCEPT Insects show an amazing range of adaptations.
24.1 Arthropod Diversity
Insects are the dominant terrestrial arthropods.
• Insects are in nearly every ecological niche.• Insects have a body with three parts.
– head– thorax– abdomen abdomen
thorax head
24.1 Arthropod Diversity
• Some insects live independently, others live in social colonies.
24.1 Arthropod Diversity
Insects undergo metamorphosis.
• In incomplete metamorphosis, insects look like miniature adults when they hatch.
• There are three life stages of incomplete metamorphosis.– larva– nymph– adult
nymph stage
larvae
adult
24.1 Arthropod Diversity
Larva
EggPupa
Adult
• In complete metamorphosis, the insect changes form entirely.
• There are three life stages of incomplete metamorphosis.– egg– larva– pupa – adult
24.1 Arthropod Diversity
Insects have adapted to life on land.
• The evolution of flight occurred in insects 400 million years ago.
24.1 Arthropod Diversity
– sucking mouth parts
• An insect’s mouth parts are adaptations related to its specialized diet.
24.1 Arthropod Diversity
– chewing mouthparts
24.1 Arthropod Diversity
KEY CONCEPT Arthropods and humans interact in many ways.
24.1 Arthropod Diversity
Arthropods and humans share many of the same resources. • Many arthropods are
herbivores that eat plants humans also depend on.– Arthropods cause millions of
dollars of crop damage.– Insecticides have unwanted
side effects.
24.1 Arthropod Diversity
– arthropod-specific insecticides– integrated pest management (IPM)– genetically modified crops
• Scientists have developed safer insecticide alternatives.
24.1 Arthropod Diversity
Some arthropods can spread human diseases.
• Vectors are organisms that carry disease from one host to another.
24.1 Arthropod Diversity
– Bubonic plague is caused by a bacterium carried by fleas.
– Yellow fever is caused by a virus carried by mosquitoes.– Malaria is caused by a protozoan parasite carried by
mosquitoes. It is the world’s most deadly disease.– West Nile virus is caused by a virus carried by
mosquitoes.– African sleeping sickness carried by tsetse fly
• Disease spread by arthropods have serious effects on human populations.
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