Invertebrate Feeding

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Invert Feeding

Microphagy

  • Feeding off of tiny food particles
  • Probably favoured by ancestral inverts
  • Disadvantges
    • Food widely dispersed, so animal must be mobile
    • Constrained by body size
    • Evolution favoured a larger body size, so..

Macrophagy

  • Advantages of large body size
    • Increased reproductive output
    • Reduced mortality
    • Competitive advantage
  • Can be classified according to diet and behavious
    • Herbivory
    • Predatory
  • Easiest form: suspension feeding
    • 2 types
      • Passive (Interceptors)
        • Consume organic matter whilst suspended in water column
        • Mucus covers spines, trapping suspended particles
        • Wiped off by a tube foot, transferred to scale and passed to mouth
      • Active
        • Common
        • Requires a filter to capture suspended particles
        • Current expelling water is more powerful, often coupled to removal of waste products
        • Cilia generate current
        • Flow = unidirectional
        • An array of feeding appendages
          • Polychaetes have tentacles
          • Bryozoa have lophophore
          • Bivalve molluscs - ctendial gills
          • Some use mucus to trap particles
            • Mucus secreted as a bad/threads through which a current is generated
            • Mucus is then consumed along with trapped particles
            • EXAMPLEChaetopterus sp.
        • Often couples as a respiratory surface
        • Arthropods
          • Do not possess cilia, so use setae on specialised appendages
            • Copepods use maxillipeds
            • Barnacles use their legs
            • Some crab species use antennae
          • Setae - bristles used to trap suspended particles

Deposit Feeding

  • Some inverts consume surface material
  • Don't need specialised feeding structures
  • Disadvantages
    • Little available organic matter
    • Limited by bacterial productivity
  • Important in the deep sea

Herbivory

  • Requires robust mouthparts
  • Echinodermata, Echinoidea: Aristotle's Lantern
    • 5 pyramids supporting the teeth
    • Under muscular control
    • Rasping and chewing
  • Mollusca eg. radula and jaws
    • Chitinous teeth
    • Scraping/rasping action
    • Buccal cavity
  • Arthropoda eg. insects
  • Do not typiccally suffer food shortages
  • Disadvantges
    • Chemical defence mechanisms
    • Large proportion of diet is indigestible
  • Often have bacteria within gut to asist in breakdown of plant material during digestion
    • Echinoderms also have N2 fixing bacteria
    • Molluscs have evolved enzymes (cellulases) to break down plant material
  • Some avoid indigestible plant material by sucking sap
    • Requires complex mouth appendages
    • Poor diet, lacks protein
    • Utilises symbiotic bactera
    • EXAMPLE

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