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? Spider Beetle Crab 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

one pair of compound eyes and 3-8 simple 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 modified into pincers (hold food) or fangs (inject poison) chelicerae

Arachnids 2nd pair – pedipalps, for handling food and sensing

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

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 insect embryos develop inside eggs, eggs hatch some look like miniature adults will molt several times until adult size Molt Nymph Eggs Nymph Molt Adult

Insecta INCOMPLETE METAMORPHOSIS Nymphs can’t reproduce 3 stages: egg, nymph, adult Nymphs can’t reproduce Nymph gradually becomes an adult

Insecta Some undergo COMPLETE METAMORPHOSIS 4 stages: egg, larva, pupa, adult Metamorphosis is controlled by chemical substances in the insect Egg Adult 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 Spiders are: Predators! predators scavengers decomposers parasites Predators!

Question 6 Having 2 pairs of antennae distinguish _________ from other arthropods. centipedes millipedes crustaceans horseshoe crabs Crustaceans!

Question 7 Why are horseshoe crabs called “living fossils?” They remain unchanged after 220 million years!