Ch 24 A Closer Look at Arthropods 24

Ch 24 A Closer Look at Arthropods 24. 1 Arthropod Diversity • Arthropods characteristics – invertebrates – exoskeleton (cuticle) made of chitin – jointed appendages (paired) – segmented body parts

• Arthropod Groups – Trilobites • extinct, bottom feeders – Crustaceans • live in oceans, freshwater streams, and on land – Chelicerates • specialized daggerlike mouthparts – Insects • most live on land, have six legs – Myriapods • long bodies and many pairs of legs

• Movement – 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 • Molting 1. Secrete new layer cuticle under exoskeleton 2. Enzyme weakens old exoskeleton, crawl out of it 3. New exoskeleton filled with fluid/larger than before, will harden

• Internal/External Functions • Arthropods have an open circulatory system. • Sensory organs such as antennae are made of modified cuticle. • Most arthropods have compound eyes.

• Arthropod Diversity – The oldest fossils are of trilobites that date back 540 million years. • The evolutionary relationship between arthropods and other invertebrates remains under question. – body segmentation similar to annelids – molecular evidence suggests segmentation is analogous development • Velvet worms and water bears are considered the closest relatives of arthropods.

24. 2 Crustaceans • Crustaceans evolved as marine arthropods • Crustaceans share several common features. – two distinct body sections, cephalothorax and abdomen – one pair of appendages per segment – two pairs of antennae – exoskeleton – carapace

• Appendages include claws, antennae, walking legs, swimmerets, and mandibles. • Crustacean appendages are used for a variety of functions. – collecting and manipulating food – attracting females – protection

• Crustaceans vary in both anatomy and structure. – Decapods such as lobsters and crabs have ten legs. • Barnacles are sessile filter feeders wrapped in a hard shell. • 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. 3 Arachnids • Arachnids are spiders and their relatives • Arachnids are the largest group of chelicerates – Lack antennae – Have 6 paired appendages – 4 pairs of walking legs – Fanglike mouthparts chelicerae – Appendages pedipalps grasp prey – 2 body sections: cephalothorax and abdomen

• There are three major groups of chelicerates. – horseshoe crabs – sea spiders – Arachnids

• Arachnids are a group of chelicerates that live on land. – eight legs – fanglike pincers that inject venom – silk glands fangs poison gland spinnerets • Arachnids have four different adaptations that reduce water loss. – waterproof cuticle – book lungs – Malpighian tubules – spiracles

• Diversity of Archanids: – All spiders make silk and produce venom. – Spiders make up half of the more than 60, 000 known arachnid species. – Arachnids also include mites, ticks, chiggers, and scorpions

24. 4 Insect Adaptations • Insects are in nearly every ecological niche. • Insects have a body with three parts. – head – thorax – Abdomen

• Some insects live independently, others live in social colonies • In incomplete metamorphosis, insects look like miniature adults when they hatch. • There are three life stages of incomplete metamorphosis. – larva – nymph – adult

• There are three life stages of complete metamorphosis. – egg – larva – pupa – adult

• Evolution to life on land – The evolution of flight occurred in insects 400 million years ago. – An insect’s mouth parts are adaptations related to its specialized diet. • • sucking mouth parts chewing mouthparts

24. 5 Arthropods and Humans • Arthropods interact with humans. • Many arthropods are herbivores that eat plants humans also depend on. – Arthropods cause millions of dollars of crop damage. – Insecticides have unwanted side effects.

• Scientists have developed safer insecticide alternatives. – arthropod-specific insecticides – integrated pest management (IPM) – genetically modified crops

• Vectors are organisms that carry disease from one host to another. • Disease spread by arthropods have serious effects on human populations. – 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. – West Nile virus is caused by a virus carried by mosquitoes.