Simple triploblasts

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  • Simple triploblasts
    • Bryozoa
      • 'Moss animals'
      • 4,500-8,000 species
      • Live in colonies of up to 2 million individual zooids
      • Quite common
        • Most marine
        • Some in fresh water
      • Oscillate and rotate their lophophore to increase contact with prey
      • Sexual reproduction
        • Sperm released into water
        • Internal fertilisation
        • Developing embryo brooded released as larvae
      • Some zooids have jaws to protect from grazing
    • Brachiopoda 'armed foot'
      • Lamp shells
      • Solitary, sessile and marine
      • Feed with motile lophophore
        • Cilia on lophophore beat to withdraw water with food particles
      • 335 extant species but 26,000 fossils
      • Two-part hinged shell
        • Similar to bivalve mollusc but dorsal & ventral rather than lateral
      • 4-6 cm long
      • Attached by short, flexible stalk to rock or into sediment
      • Trochophore larvae settle after a few days and develop into adults
    • Rotifera
      • 'Wheel-bearers'
      • Small, mostly fresh water
      • Some free moving, some sessile
      • 1,800 species
      • Complete gut
      • Move by beating cilia
      • Coronal cilia sweep particles into mouth
      • Food ground up in gut by mastax
      • Frequently have fixed number of cells (~1000)
      • Males and females in most species
        • Some only have females
          • Reproduce partheno-genetically
      • Genetic diversity sustained by picking up fragments of genes from environment
    • Platy-helminthes (flatworms)
      • Significant parasites of vertebrates
        • Important to medicine, veterinary science & agriculture
        • Free-living flatworms can predate other invertebrates
        • Most are endo or exoparasites of vertebrates
      • Some free living marine, fresh water or terrestrial
      • 25,000 species
      • Lack organs for transporting oxygen
        • Flat form enabled gas exchange by diffusion
      • Digestive tract has one opening, gut often branched
      • Excretory organs called proto-nephridia
        • Flame cell and duct - pore
      • Some have ganglia, nerve trunks and sense organs
      • 4 CLASSES
        • Turbellaria
          • 4,500 species
          • 4-600 mm long
          • Some are parasitic
          • Many have more than one host
          • Mostly predators or scavengers
          • Skin is single cell layer
          • Ciliated on lower body and sometimes all over body
            • Enables movement
          • Some species swim by muscular undulations
          • Sense organs
            • Simple eyes
            • Balance organs
            • Chemo-sensors
          • Herma-phrodites, internal fertilisation
          • Small portions can regenerate into a completely new worm
        • Trematoda
          • Flukes, often internal parasites
          • Ventral suckers for attachment
          • Complex life cycles specialised for parasitism
          • Enormous number of offspring
          • Definitive host plus a number of staged intermediate hosts
        • Mongenea
          • External parasites, mainly of fish
        • Cestoda (tapeworms)
          • 3,400 species
          • Two or more hosts
          • Specialised parasites of vertebrates
          • Most organ systems reduced
          • No gut
            • Nutrients absorbed through skin
          • Head relatively tiny scolex that attaches to host's gut lining
          • Neck continually produces chain of reproductive segments called proglottids

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