unit 24 arthropods
TRANSCRIPT
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.