2 Phylum Arthropoda

• Arthropoda

  • Gk: arthros – joints, podos – foot
• Phylum Arthropoda - largest assemblage in the Animal Kingdom = 80% of all known species; 800,000 have been described; estimated total number of species is about 6 million
• Characteristics of Phylum Arthropoda:

  1. Metamerism
  2. Exoskeleton
  3. Bilateral symmetry
  4. Paired jointed appendages
  5. Open & dorsal circulatory System
  6. Ventral nervous system
• Metamerism – body is segmented, arranged into regions called tagmata (head, thorax, abdomen)
• Exoskeleton – chitinous covering (hard) that must be shed at intervals (ecdysis) or during growth (molting)
• Hypothetical Evolution of Insect

  1. Segmented, legless, wormlike annelids
  2. Paired, bilateral, lobe-like appendages on the somite, with a pair of simple eye and antenna
  3. Bilateral appendages on each body segment becomes jointed, and with typical primitive mandibulate
  4. Differentiation of head, thorax and abdomen, with modified genitalia
• Crustacea – e.g., lobsters, crabs, copepods
• Crustacea - mostly aquatic gill-breathers
• Crustacea - with 2 well-defined body regions: cephalothorax and abdomen
• Crustacea - possess 2 pairs of cephalic appendages, antennae, and several pairs of branching appendages on remaining cephalothoracic segments, with few abdominal appendages
• Crustacea - calcium salts impregnate the exoskeleton = rigidity
• Arachnida – e.g., spiders, mites, ticks, scorpions
• Arachnida - with 2 well-defined body regions: cephalothorax and abdomen
• Arachnida - lack antennae with 6 pairs of appendages: 1 st pair – chelicerae (jawlike or fangs), 2nd pair – pedipalps (not leglike), remaining 4 pairs – legs
• Myriapoda - with 2 body regions: head & trunk
• Myriapoda - elongated, worm-like bodies, with 9 or more pairs of appendages
• Diplopoda (milliepedes) - cylindrical or slightly flattened bodies
• Diplopoda (millipedes) - with more than 30 pairs of legs, typically 2 pair of legs per body segment, and short antennae
• Chilopoda (centipedes) - fewer legs than millipedes usually more than 15, with 1 pair per body segment
• Insecta - contains the vast majority of medically important arthropods
• Insecta - with 3 body regions (head, thorax and abdomen), 3 pairs of thoracic appendages, compound eyes and simple eyes (ocelli)
• Phylum Arthropoda Members of Medical Importance:

  1. Crustacea
  2. Arachnida
  3. Myriapoda
  4. Insecta
• Class Insecta: Integument/Exoskeleton

  • Body covering, made up of hardened/sclerotized plates (sclerites) separated by flexible ("membranous") regions, conjunctivae, or by grooves (sutures) = allows flexibility and protection
• Class Insecta: Integument/Exoskeleton

  • Epidermis – single layer of cells that synthesizes and deposits the cuticle
• Class Insecta: Integument/Exoskeleton

  • Dermal glands – interspersed among the epidermal cells, secreting the outermost layer of cuticle including substances and various pheromones
• Class Insecta: Integument/Exoskeleton

  • Apodemes – infoldings of the body wall (structural support) and attachment of muscle fibers
• Class Insecta: Integument/Exoskeleton

  • Setae – multicellular, hairlike, one cell forming the projected portion (hair) and another cell forming the socket, pigmented and connected to a neuron and acting as sensory structures
• Class Insecta: Integument/Exoskeleton

  • Spines – multicellular, the cuticle of which is continuous with the integument
• Class Insecta: Integument/Exoskeleton

  • Microtrichia – subcellular, tiny cuticular hairs that cover the cuticle
• Class Insecta: General Insect Form

  • 3 regions: head, thorax & abdomen
• Class Insecta: General Insect Form

  • Head – bears the mouthparts (ingestion) & sensory organs = a pair of compound eyes, simple eyes (dorsal ocelli), and a pair of antennae
• Class Insecta: General Insect Form

  • Thorax (prothorax, mesothorax, & metathorax) – each thoracic segment bears pair of legs, when wings are present are borne on meso- and/or metathorax
• Class Insecta: General Insect Form

  • Abdomen – composed of 11 segments: last segment is divided into a dorsal epiproct and lateroventral paraprocts and cerci/cercus, 8 and/or 9 segments bear the external genitalia
• Class Insecta: Head

  • Head capsule – provides rigid points of attachment for mouthpart musculature
• Class Insecta: Head

  • Cervix – joined the head capsule with the prothorax
• Class Insecta: Head

  • Cervical sclerites – small plates in the cervix that provide articular points for both the posterior head capsule and the anterior edge of the prothorax
• Class Insecta: Head

  • Foramen magnum – opening at the back of the head capsule where skeletal muscles, alimentary canal, aorta, and nerves enter
• Class Insecta: Head

  • Frons - region between the compound eyes
• Class Insecta: Head

  • Gena - lateral regions between the compound eyes
• Class Insecta: Head

  • Vertex - located between the compound eyes at the dorsal of the head