Invertebrates evolutionary history

• Origin of invertebrates

  • Roughly 3 billion years after the first prokaryotic cells evolve all prokaryotes and eukaryotes were single celled.
  • Animals evolved from ancestor they shared with organisms called choanoflagellates.
  • Choanoflagellates hare several characteristics with sponges, the simplest multicellular animals .
• EDIACARIAN FAUNA

  • Some important discoveries about invertebrate life before the cambrian period come from fossils in the ediacara hills of australia
  • Strange fossils which date from roughly 565 to about 544 million years ago show body plants that are different from those of anything alive today.
• EDIACARAN FAUNA

  • Many of the organisms were flat and live on the bottom of shallow
  • they show little evidence of cell tissue or organs specialization and organization into a front and back end
• CAMBRIAN EXPLOSION

  • The cambrian period began about 544 million years ago.
  • Two major cambrian fossils sites are in chengjiang china and in the burgess shell of canada
  • cambrian fossils show that over a period of 10 to 15 million years animals evolved complex body plants including specialized cells tissues and organs
• CAMBRIAN EXPLOSION

  • A number of cambrian fossils have been identified as ancient member of modern invertebrates phyla such as the fossil of arthropod which is marella spledens.
• CAMBRIAN EXPLOSION

  • Late evolutionary changes which produce the more familiar body structures of modern animals involves variations on this basic body plants.
• • Today invertebrates are the most abundant animals on earth
  • invertebrates live in nearly every ecosystem participate in nearly every food web and vastly out number so called "higher animals" such as reptiles and mammals.
• • Modern sponges and cnidarians have little internal specialization
  • specialized cells joined together to form tissues organs and organ systems that works together to carry out complex functions.
• All invertebrates except sponges exhibit some type of body symmetry
• • The concentration of sense organs and nerve cells in the front of the body is called cephalization
  • some organisms like worms and arthropods nerve cells are arranged in structures known as ganglia
  • in more complex invertebrates such as certain mollusk nerve cells form an organ called brain
• Coelom formation

  • Most complex animal phyla have through coelom that is lines completely with mesoderm.
• Early development

  • In most invertebrates the zygote divides repeatedly to form a blastula- a hollow ball of cells
• Sponges or phylum porifera

  • are the most ancient members of the kingdom animalia
  • they are multicellular heterotrophic, lacks cell walls, and contain a few specialized cells.
• • Cnidarians or phylum cnidaria it includes jellyfishes sea fans, animals hydras and corals.
  • they are aquatic, soft bodied ,carnivorous, radially symmetrical animals, with stinging tentacles
  • they are the simplest animal to have body symmetry.
• Flatworms or phylum platyhelminthes

  • They're unsegmented flattened worms that have tissues and internal organ systems
  • they are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization
  • flatworms do not have coelom.
• Mollusks or phylum mollusca

  • Includes snails, slugs, clams, squids and octopus
  • they are soft bodied animals that have an internal or external shell
  • they have true coelom surrounded by mesoderm and complex organ systems, many mollusks have a free swimming larva or immature stage called a trochopore.
• Annelids or phylum annelida

  • this includes earthworms, submarine worms, and leeches,
  • They are worms with segmented bodies and a true coelom line with tissue derived from mesoderm
• Nematodes or phylum nematoda

  • these re unsegmented worms with pseudocoeloms, specialized tissues, and organs, and digestive tracts with two openings, a mouth and anus
  • they were once thought to be closely related to flatworms, annelids, and mollusks but have been found to more closely related to arthropods.
• Arthropods or phylum arthropoda

  • possesses an exoskeleton with the cuticle made of chitin which is being shed periodically
  • have a segmented body jointed limbs
  • it includes insects crustaceans and spiders
• Echinoderms or phylum echinodermata

  it includes sea stars sea urchins and sand dollars they have spiny skin and internal skeletons

  • they also have a water vascular system or a network of water filled tubes that includes suction cup like tube feet which are used for walking and gripping pret
  • most exhibit five part radial symmetry and are deuterostomes