Transcript ARTHROPODA
Phylum ARTHROPODA Shari Bolar Natalie Allcott Brian Schuster Bilateral Symmetry Major Classes • • • • • Arachnida: spiders, scorpions, ticks, mites Diplopoda: millipedes Chilopoda: centipedes Insecta: insects Crustacea: crabs, lobsters, crayfish, shrimp, barnacles Orders of Insects (a chosen few; there are many more) Common Features of Arthropods • Cuticle: the exoskeleton (external skeleton) that is made of layers of protein and chitin, and provides protection for the organism. Can be thick or thin, provides attachments for muscles, and is impermeable to water. • Molting: shedding of cuticle in order to secrete a larger one. Makes the arthropod vulnerable. • Open circulatory system: hemolymph fluid flows through open spaces (sinuses) which surround organs and tissues. Important for nutrient transport. Common Features of Arthropods (cont.) • Malpighian tubules: excretory organs that remove waste from hemolymph in the circulatory system • Tracheal system: branched tubes with chitin lining that carry O2 directly to cells (insects only) • Spiracles: openings in exoskeleton that allow air to enter tracheal system (insects only) Unique Arthropod Features • Book lung: respiratory organ of most spiders that contains stacked plates in an internal chamber that exchanges gases (mostly O2 and CO2) with a spider’s body and the air • Chelicerae: claw-like feeding appendages contained by chelicerates (arachnids) • Mandibles: jaw-like feeding apparatuses contained by unimarians (centipedes, millipedes, insects) and crustaceans Unique Arthropod Features (cont.) • Antennae: sensory organs that come in pairs on the organism’s head • Compound eyes: eyes with many parts and multiple separate focusing elements Life Cycle Metamorphosis: a relatively abrupt change in form or structure Incomplete Metamorphosis Young are similar to adults, but have different body proportions and are smaller. There are a series of molts that eventually lead to the organism reaching full size. Complete Metamorphosis There are several distinct stages: Larval stage specialized for eating and growing Pupal Stage actual change occurs Adult stage specialized for reproduction Germ Layers and Coelom • triploblastic: have all three germ layers (ectoderm, endoderm, an mesoderm) • protostomes: the opening of the gastrula, the blastopore, becomes the mouth and the second opening becomes the anus • start with a coelom during embryo development, which becomes reduced over time. • have open circulatory systems where hemolymph fluid is propelled through sinuses. These sinuses together are called the hemocoel. As the coelom becomes reduced the hemocoel becomes the main body cavity. Even though this occurs they are still coelomates. Reproduction Reproduction is usually sexual with differences in male and females. Potential mates are advertised by bright colors, sound, and odor. Fertilization is internal and is done by normal intercourse. The female will lay eggs. Mating normally happens only once in a lifetime. Camel Spider (class Arachnida; order Solifugae) It does not spin webs or have book lungs. Many rumors about the camel spiders’ speed, size and venom. In the middle east, it was said that these big, fast spiders would come into your tent at night and inject an anaesthetizing venom that would put its victims to sleep and feed on victim leaving a gaping wound. This is false, except that they do leave a large bite prone to infection. Spider Feeding Spiders use a fang like chelicerae equipped with poison glands to kill prey caught in web. Instead of fully chewing their prey, the spider will spill digestive juices onto prey. This softens the food and the spider will suck up the liquid. Review Questions • What type of symmetry do arthropods have? • Match the following classes with their members: – Insecta – Arachnida – Diplopoda – Crustacea – Chilopoda centipedes crabs, lobsters, barnacles insects millipedes spiders, scorpions • In what stage of metamorphosis does abrupt change occur? • What do most spiders use to breathe? • What process allows arthropods to shed their cuticle in order to grow a larger one? Review Questions • Is fertilization internal or external? • How are arthropods classified: protostomes or deuterostomes? • How many germ layers does a camel spider have? • What do spiders use to feed on their prey?