Geology - Corals

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  • Corals
    • Phylum = Cnidaria
    • Class = Anthozoa
    • Morphology
      • Their bodies consist of two layers, an outer ectoderm and an inner ectoderm.
      • They have stinging cells called nematoblasts
      • There are two main types of coral: Solitary and compound.
        • Solitary: have one polyp, which secretes a single skeleton.
        • Compound: many polyps living together in a communal fashion with many skeletons or corralites fused together.
          • A polyp is a soft bodied organism that secretes a calcium carbonate skeleton.
            • Solitary: have one polyp, which secretes a single skeleton.
      • The calice is a bowl shaped depression where the soft polyp sits.
      • The epitheca is the outermost layer of the coral skeleton.
      • The columella is the axial rod which supports the septa, running up the centre of some corals.
      • The corallite is the skeleton produced by one coral polyp.
    • There are three main types of coral.
      • Tabulata
        • Extinct
        • Well developed tabulae
        • Corallites are usually small and mural pores may be present in some species.
        • They show radial symmetry
          • Many planes of symmetry can be seen
        • Development of septa is poor or absent
        • Do not have a columella
      • Scleractinian
        • Extant
        • Either solitary or colonial
        • May have dissepiments and they always have tabulae.
    • How do modern corals live?
      • Some species of coral have a type of algae living inside of them.
        • These algae are called Zooxanthellae
        • There is a symbiotic relationship between the algae and the coral.
          • The algae can photosynthesise as they contain chloroplasts in their cells.
            • The algae takes the CO2, phosphates and nitrates produced as waste from the coral and uses them to produce oxygen, water, amino acids and sugars.
              • The coral uses the waste from the algae.
                • These organisms cannot survive without each other.
    • Soft bodied Polyp
      • After death, the soft tissue is not preserved.
      • Soft bodied polyps sit on top of the hard secreted skeleton or calice.
      • The polyp itself has tentacles which it extends for feeding purposes, usually at night.
        • Untitled
    • Conditions needed for coral growth
      • Above 30m in depth as they need sunlight
      • Clear water so the algae can get sun and photosynthsis
      • High energy so that there is more oxygen in the water and circulates the nutrients.
      • Salinity of 30-40 parts per thousand
      • Temperatures between 23 and 27 degrees
  • Rugose
    • The epitheca is often wrinkled in solitary forms and they may be "horn-shaped"
    • Can be colonial or solitary
    • Extinct
    • Corallites are usually large with no mural pores or connections between the corallites.
    • There are three main types of coral.
      • Tabulata
        • Extinct
        • Well developed tabulae
        • Corallites are usually small and mural pores may be present in some species.
        • They show radial symmetry
          • Many planes of symmetry can be seen
        • Development of septa is poor or absent
        • Do not have a columella
      • Scleractinian
        • Extant
        • Either solitary or colonial
        • May have dissepiments and they always have tabulae.
    • They show one plane of symmetry known as bilateral symmetry.
      • This symmetry is picked out by the distinct septa, the plates that run vertically in the skeleton.
    • They always have a columella and may have dissepiments between the septa but not always present.

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