Transcript Arthropods
Arthropods Arthropods • Arthropods are the most diverse and numerous animals on earth • More than 1 million different species have been identified • They thrive in almost every habitat • There worldwide population is estimated at a billion billion, or 1018 individuals General Characteristics of the Phylum Arthropoda (Arthropods) • Arthropods are characterized by there segmented bodies, jointed appendages and hard exoskeletons • The exoskeleton is composed of chitin • In most arthropods the segments are called the head, thorax and abdomen • The head contains the antennae and mouth pieces, the thorax supports the legs and wings and the reproductive organs are found in the abdomen General Characteristics of the Phylum Arthropoda (Arthropods) • As arthropods grow, they will outgrown the chitinous exoskeleton. They will shed the exoskeleton in a process called molting General Characteristics of the Phylum Arthropoda (Arthropods) • All arthropods have an open circulatory system in which blood is pumped from a tubelike heart to bath the internal organs • All arthropods have a ventral nerve cord and brain • Along the nerve cord are specialized nerve cells called ganglia • Most arthropods have compound eyes General Characteristics of the Phylum Arthropoda (Arthropods) • Aquatic arthropods have gills used for respiration • Terrestrial arthropods have tracheae, which are chitin lined tubes that lead from the internal organs to the outside of the body where they end in little holes called spiracles that are used for breathing Overview of Arthropod Diversity • Arthropods first evolved in the sea about 560 million years ago • A good example of an early extinct arthropod is called a trilobite Overview of Arthropod Diversity • One ancient living arthropod is the horseshoe crab, which have been living virtually unchanged for over 300 million years Overview of Arthropod Diversity • Modern arthropods include the crustaceans, arachnids, insects and myriapods Crustaceans • The crustaceans include the lobsters, crabs, shrimp and barnacles • Crustaceans have specialized appendages (claws or chelipeds) often used for fighting Terrestrial Arthropods • The three groups of terrestrial arthropods include the arachnids, insects and myriapods • The arachnids include the spiders, ticks, scorpions and mites • The insects include beetles, ants, grasshoppers, butterflies and dragonflies • The myriapods include centipedes and millipedes Metamorphosis • Insects undergo metamorphosis a process by which the body changes from a sexually immature phase to the mature adult phase • Once metamorphosis is complete the adult no longer grows • Both molting and metamorphosis are controlled by hormones Metamorphosis • Incomplete metamorphosis (grasshoppers) the immature young look like the adults but lack wings and sexual organs • Complete metamorphosis (butterflies) the larval stage looks and functions much differently from the adult stage