Introduction to Invertebrates

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Avalon and Cambrian Explosions

  • Avalon explosion: proposed evolutionary radiation of Animalia, taking place around 575mya in the Ediacaran
    • had two main radiations of animal life: the rangeomorphs and the erniettomorphs
  • Cambrian explosion: refers to the interval of time in the Cambrian period when practically all major animal phyla started appearing in the fossil record
    • lasted between 13 and 25 million years
    • occurred around 538.8 million years ago
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Laggerstätten

  • Laggerstätte:sedimentary deposit that exhibits extraordinary fossils with exceptional preservation 
    • two types: Konzentrat-Lagerstätten and Konservat-Lagerstätten 
  • Konzentrat-Lagerstätten: concentration Lagerstätten, have a particular concentration of disarticulated organic hard parts, such as a bone bed
  • Konservat-Lagerstätten: conservation Lagerstätten, known for exceptional preservation of fossilised organisms or traces 
    • taphonomy varies 
    • explain important moments in history and the evolution of life
    • sediment from toxic volcanic ash of submarine volcanoes and landslides
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Ancestors of Animals

  • common ancestors of plants and animals appeared 2500 million years ago
  • theoretically, there are three ways multicellular organisms could have evolved from protists:
    • different protists form symbioses to create a composite multicellular organism
    • products of asexual division stay together, and multicellularity comes from intermediate colonial stage
    • multinucleate protist evolve internal membranes around each nuclei
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Abundance of Invertebrates

  • 1.3 million described invertebrate species, of which almost 90% are arthropods 
  • most familiar groups include:
    • ANNELIDA (segmented worms),  
    • ARTHROPODA (e.g., insects, spiders, crustaceans), 
    • CNIDARIA (corals, sea anemones, jellyfish), 
    • ECHINODERMATA (e.g., starfish and sea urchins), 
    • KINORHYNCHA (mud dragons), 
    • MOLLUSCA (e.g., snails, clams, squids),
    • NEMATODA (roundworms),
    • NEMATOMORPHA (horsehair worms),
    • PLATYHELMINTHS (flatworms),
    • PORIFERA (sponges),
    • PROTOZOA (e.g., amoeba),
    • ROTIFERA (wheel animals),
    • and TARDIGRADA (water bears) 
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Haeckel's Tree

  • created in 1866
  • had three kingdoms: Animalia, Vegetabilia, and Protista
  • all microscopic organisms were known as Monera
    • Monera persisted as a group until 1977 when Carl Woese split Monera into Archaea and Bacteria
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Biological Symmetry

  • animals can be asymmetricradially symmetrical, or bilaterally symmetrical
  • BILATERIA can be split into PROTOSTOMIA and DEUTEROSTOMIA
    • protostomes have their mouth form from the blastophore
    • deuterostomes have their anus form before their mouth
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