Arthropoda

• Arthropoda


  Derived from Greek words: arthros-a joint; podos-a foot
• Classes of Arthropoda

  • Insecta
  • Arachnida (Chelicerata)
  • Crustacea
  • Myriapoda
• Insecta

  • 6 legs, 3 body regions, mandibles, 1 pair of antennae, 0, 2, or 4 wings
• Arachnida (Chelicerata)

  • 8 legs, 2 body regions, chelicerae, no antennae, no wings
• Crustacea

  • 10+ legs, 2 body regions, mandibles, 2 pairs of antennae, no wings
• Myriapoda

  • Greek: Myria- ten thousand; Pous-foot, 1-2 pair of legs per segment, 2 body regions, mandibles, 1 pair of antennae, no wings
• Centipedes move faster than millipedes


  Because centipedes have longer legs
• Insecta

  • Bilateral symmetry
  • Coelomate
  • Tribloblastic
  • Displays cephalization
• Organisms with cephalization will always have bilateral symmetry
• Protostomes

  Their mouth develops first through gastrulation
• Many insects but not all go through a larval stage
• Insects must undergo metamorphosis before they go through another stage
• Sclerites

  The exoskeleton is usually present in the form of chitinous plates: Tergum, Sternum, Pleuron
• Insect digestive system

  1. Foregut (Stomodaeum)

  2. Midgut (Mesenteron)

  3. Hindgut (Proctodaeum)
• Foregut (Stomodaeum)


  • Initial breakdown of large food particles occurs, mostly by saliva
• Midgut (Mesenteron)

  • Digestion through enzymatic action, microvilli increase surface area and allow for maximum absorption of nutrients
• Hindgut (Proctodaeum)

  • Rectum absorbs most of the water in waste matter, dry pellet is then eliminated through the anus
• Parts of the Hindgut (Proctodaeum)

  • Malpighian tubules
  • Pylorus region
  • Ileum
  • Rectum
• Malpighian tubules


  Responsible for absorbing the nitrogenous waste from the hemolymph, which is then transported into the hindgut to be excreted
• Arthropod excretory structures

  • Pair of nephridia (crustacean)
  • Malpighian tubules (insecta)
  • Malpighian tubules and coxal glands (arachnids)
• Arthropod respiratory structures

  • Gills (branchiae)
  • Trachea
  • Lung-books (spiders)
  • Gill books (crabs)
  • Cuticle (parasitic mites)
• Insect tracheal system

  • Composed of a thin layer of chitin strengthened by spiral thickenings
• Insect respiration

  Movements produced by muscular contractions and elastic distensions of the body wall
• Proper identification of arthropods is essential in pest management
• Insects

  • Three, usually distinct body regions: head, thorax, & abdomen
  • One pair of segmented antennae
  • Usually have one pair of compound eyes
  • Three pairs of segmented legs, one pair on each of the three thoracic segments
  • Usually with two pairs of wings, some have only one pair or no wings at all
• Insect head

  • Ovoid or globular capsule composed of a number of plates or sclerites
  • Eyes: compound eyes (holophobic or dichoptic), small simple eyes or ocelli
  • Antennae: situated between or in front of the compound eyes, form varies
  • Mouthparts: modified for chewing or sucking, includes labrum, labium, mandibles, maxillae, epipharynx, hypopharynx
• Maxillae and labium possess jointed palps which function as sensory structures
• Labium or lower lip

  Forms the lower boundary of the mouth
• Biting Jaw (pair)

  • Between the labrum and labium
• Epipharynx


  • A small membranous structure found on the underside of the labrum
  • It bears the organ of taste
• Hypopharynx

  • Bears the salivary duct
• Maxillae and labium

  • Possess jointed palps
  • Function of jointed palps is sensory
• Thorax

  • Primarily responsible for locomotion
  • Made up of 3 segments: prothorax, mesothorax, and metathorax
• Legs

  • Consist of trochanter, femur, tibia and tarsus
  • Tarsal segment is provided with a pair of claws
  • Between the claws is a pad, a spine or a bristle
  • Pulvilli are located below the claws
• Wings

  • Normally there are 2 pairs
  • In Dipterans, the posterior is reduced to form the balancers or the halters
  • The wings are supported by "veins" which are branching tubes or trachea
  • Wing arrangement is important for identification
• What are the balancers or halters formed from in Dipterans?
• Abdomen

  • Has 11 or fewer segments
  • Contains the copulatory claspers, an ovipositor, and the external genitalia – the modified terminal somites
• Alimentary Canal

  • Consists of stomodaeum, a mesenteron and proctodaeum
  • Diptera feature a crop
  • Mosquitoes have three thin bags
  • Acarina have diverticula (blind sacs) in the midgut that can greatly distend
  • Insects that eat solid food have a gizzard with a complicated set of teeth on its internal surface
  • Cyclorrhapha have an esophageal valve
  • Proventriculus is compact and spherical, functioning as a valve
  • Peritropic membrane extends from midgut to rectum in Cyclorrhapha
• Vascular System

  • Comprises the heart, an aorta and the general body cavity or hemocoele
• Circulatory System

  • Hemocoel is a cavity that carries blood (hemolymph)
  • Ostia (openings in the heart) close when heart contracts and open when heart relaxes to suck in blood