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  • Graptolites
    • Morphology
      • Nema
        • Thin tube extension of the sicula. Possibly used to attach to a floating object
      • Stipe
        • Branch of Rhabdosome
      • Sicula
        • Conical tube secreted by the first member of the colony
      • Virgella
        • Spine at the end of the sicula
      • Theca
        • Individual cup in which one zooid lived
      • Aperture of the Sicula
        • Where the fist zooid protruded through the skeleton
      • Rhabdosome
        • The whole Graptolite skeleton
    • Mode of life
      • Mostly planktonic, attached to a floatation device via the Nema
    • Importance
      • Used in biostratigraphy as a some fossil
      • Close similarity with modern day pterobranchs
    • First appeared in the ordovician
    • Hemichordata, Graptodoidea
    • Evolution
      • Number of stipes reduces over time. Many in the ordovician to one in the silurian
      • attitude of the steps changes from pendant to horizontal to reclined to scandent from ordovician to silurian
      • Shape of the thecae change from simple tube shape to more elaborate shapes
      • from early uniserial thecae to biserial in the ordovician


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