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Arthropods What are ARTHROPODS? • • • • • Coelomate Segmented Bilateral Symmetry Exoskeleton – made of protein and chitin Jointed appendages – any structure (leg or antennae) that grows out of the body What are Arthropods? • earliest invertebrates to exhibit jointed appendages – Jointed appendages are an advantage because they allow more flexibility for animals with hard, rigid exoskeletons – Joints allow powerful movements and allow appendages to be used in many ways What are Arthropods? Appendages Jointed Appendages Exoskeletons Provide Protection • made up of protein and CHITIN • can be a continuous covering over most of body OR made of plates that are held together by hinges Continuous Hinged Exoskeleton Advantages • Protects, supports internal tissues • Provides place for muscle attachment • Aquatic arthropods have exoskeleton reinforced with calcium carbonate Exoskeleton Disadvantages • Heavy – the larger the animal, the thicker and heavier the exoskeleton • Exoskeletons don’t grow – animals must molt when they get too large for exoskeleton Molting • Animal contracts muscles and takes in air or water • Body swells and causes exoskeleton to split open, usually along the back • Most arthropods will molt 4-7 times before becoming an adult. Before the new exoskeleton hardens... • increased circulation to all parts of the body cause the animal to puff up and new exoskeleton hardens leaving some “growing room” • animal can’t protect itself, can’t move Question 1 Which of the following organisms would be most likely to have an exoskeleton reinforced with calcium carbonate? A. Spider B. Beetle C. Crab D. Dragonfly Correct! Question 2 • Exoskeletons are heavy. Why can aquatic arthropods grow so much larger than terrestrial arthropods? The buoyancy of the water helps support the weight of the exoskeleton Question 3 • What is one advantage and one disadvantage of flying arthropods having a thinner, lighter weight exoskeleton? Disadvantage: less protection Advantage: greater freedom to fly and jump Question 4 • What is one advantage and one disadvantage of having a cephalothorax? Disadvantage: less flexibility, mobility Advantage: more protection Segmentation • 3 segments – abdomen – thorax – head Segmentation • Sometimes these segments can be fused together – some have head and fused thorax and abdomen – some have abdomen and fused head and thorax (cephalothorax) Respiration • Efficient respiratory systems to meet large O2 demands • Large O2 demand needed to sustain high metabolism for fast movements • 3 types of respiratory structures – gills (aquatic arthropods) – tracheal tubes (terrestrial arthropods) – book lungs (terrestrial arthropods) Respiration • Gills – water moves over gills – O2 from water diffuses into gills and into bloodstream – CO2 from body diffuses out through gills into surrounding water Respiration • Tracheal tubes – branching network of hollow air passages that take air throughout the body Muscle movement brings air in/out through SPIRACLES (openings in abdomen and thorax) Respiration • Book lungs – spiders and relatives – air filled chambers with leaf-like plates – stacked plates are arranged like pages of a book Antennae • Acute sensing by antennae – stalk like structure that can detect changes in the environment • movement • sound • chemicals Used for sound and odor communication Eyes • Compound Eyes – visual structure with many lenses • Simple Eyes – visual structure with one lens for detecting light one pair of compound eyes and 3-8 simple eyes Nervous System • Double ventral nerve cord • Anterior brain • Several fused ganglia that control the body section they are located in Circulatory System • Open circulatory system – blood flows away from the heart in vessels – blood flows out of vessels into tissues – blood returns to the heart through open spaces Digestive System • Complete digestive system with mouth, intestine, and anus • Mouth has 1 pair of jaws called MANDIBLES – adapted for holding, chewing, sucking, or biting Reproduction – Sexual and Asexual • Sexual reproduction – separate sexes – internal fertilization for terrestrial species – external fertilization for aquatic species Reproduction – Sexual and Asexual • Asexual reproduction – PARTHENOGENISIS • a new individual develops from an unfertilized egg • seen with ants, aphids and bees Arachnids • spiders (largest group), ticks, mites, and scorpions • 2 body regions: cephalothorax and abdomen • 6 pairs of jointed appendages – 12 total appendages! Arachnids • 1st pair - chelicerae, are near the mouth chelicerae • modified into pincers (hold food) or fangs (inject poison) Arachnids • 2nd pair – pedipalps, for handling food and sensing pedipalps Arachnids • Silk, for webs, is secreted by silk glands in the abdomen • as it is secreted, it is spun into thread by SPINNERETTES • spiders are predatory and feed almost exclusively on other animals Arachnids • Ticks and mites have only 1 body section • Head, thorax and abdomen are completely fused • Ticks feed on blood of other animals Arachnids • Mites feed on fungi, plants, and animals • small – not usually visible • can transmit diseases Dust mites Arachnids • Scorpions have many abdominal body segments • Enlarged pincers • Long tail with venomous stinger at the tip Crustaceans • crabs, lobster, shrimp, crayfish, barnacles • Only arthropods with 2 pairs of antennae • mandibles – move from side to side • 2 compound eyes Crustaceans • 5 pairs of walking legs • 1st pair are claws for defense claw legs Crustaceans • Most are aquatic and use gills • pill bugs (roly-polies) live on land, but must have moisture to aid in gas exchange Yes! This is a crustacean! Centipedes and Millipedes • Centipedes are carnivorous – eat soil arthropods, snails, slugs, and worms • Bites can be painful • Millipedes – eats plants and dead material on damp forest floors • Does not bite, but does spray foul-smelling fluid Horseshoe Crabs • Class Merostomata • “Living Fossils”- unchanged for 220 million years (Triassic period) • Extensive exoskeleton • Live in deep coastal waters • forage bottoms for algae, annelids and molluscs Insecta • Flies, grasshoppers, lice, butterflies, beetles • 3 body segments • 6 legs • Very diverse - more insects than all other classes of animals combined Insecta • mate once in lifetime • internal fertilization • some exhibit parthenogenesis • large number of eggs to increase survival rate Insecta Nymph Molt Eggs Nymph Molt Adult • insect embryos develop inside eggs, eggs hatch • some look like miniature adults – will molt several times until adult size Insecta • INCOMPLETE METAMORPHOSIS – 3 stages: egg, nymph, adult • Nymphs can’t reproduce • Nymph gradually becomes an adult Insecta • Some undergo COMPLETE METAMORPHOSI S Adult Egg – 4 stages: egg, larva, pupa, adult • Metamorphosis is controlled by chemical substances in the insect Larva Pupa Insecta • Incomplete metamorphosis: grasshoppers and cockroaches • Complete metamorphosis: ants, beetles, flies, wasps Origins of Arthropods • Successful because of – varied life styles – high reproductive output – structural adaptations – hard exoskeletons – jointed appendages Origins of Arthropods • Hard exoskeletons fossilize – a lot is known about evolutionary history • Evolved from ANNELIDS (segmented worms) • Arthropods have more complex segments, more developed nervous systems • circular muscles in annelids do not exist in arthropods Question 5 a. b. c. d. Spiders are: predators scavengers decomposers parasites Predators! Question 6 a. b. c. d. Having 2 pairs of antennae distinguish _________ from other arthropods. centipedes Crustaceans! millipedes crustaceans horseshoe crabs Question 7 • Why are horseshoe crabs called “living fossils?” They remain unchanged after 220 million years!