Lecture 9 - Annelida

    Cards (43)

    • What are the 3 classes under Phylum Annelida?
      • Class Polychaeta
      • Class Oligochaeta
      • Class Hirudinea
    • Members of phyla Echiura and Sipuncula are benthic marine animals with unsegmented bodies.
    • Molecular sequence data place echiurans within phylum Annelida.
    • Echiurans - Sister taxon to Annelida
    • Sipunculans - Sister taxon to a clade composed of Annelida and Echiura.
    • Annelids are protostome coelomates in superphylum Lophotrochozoa.
      • Spiral, determinate cleavage.
    • The evolutionary innovation shown by annelids is segmentation (metamerism).
      • Segmentation evolved separately in annelids, arthropods, and chordates.
    • Many annelids have chitinous bristles called setae.
      • Help in locomotion
      • Anchor worm in place
      • Deter predators
      • Polychaetes use setae for filtering food, movement, and attachment
      • Oligochaete help prevent slipping while burrowing
      • Hirudinea use suckers for attachment to prey
    • Prostomium – anterior part followed by segmented body.
    • Pygidium – terminal portion.
    • Peritonia (layers of mesodermal epithelium) of adjacent segments meet to form septa.
    • Fluid-filled coelom acts as a hydrostatic skeleton.
    • Polychaeta is a paraphyletic class. (Aclitellata)
    • Oligochaeta and Hirudinida form a monophyletic group called Clitellata.
      • Characterized by reproductive structure called a clitellum.
    • Polychaeta is the largest, most diverse class.
      • May be brightly colored, variable shape.
    • Polychaetes have some features other annelids do not:
      • A well developed head.
      • Paired appendages, parapodia, that function as gills and aid in locomotion.
      • No clitellum.
      • Many setae
    • Feeding structures of Polychates
      • Errant - Have jaws for feeding
      • Sedentary - Posses tentacles
      • Sedentary forms often have elaborate devices for feeding and respiration. Filter or deposit feeders.
      • Errant forms include pelagic and benthic types and are often predators or scavengers.
    • Representative Polychaetes
      • Clam Worms: Nereis
      • Scale worms
      • Fireworms
      • Tubeworms
      • Fanworms or Featherduster worms
      • Parchment Worms
    • Clam Worms: Nereis
      • Errant polychaetes
      • Live in mucus-lined burrows near low tide level.
      • Come out of hiding places at night to search for food.
      • Prostomium bears a pair of palps sensitive to touch and taste, a pair of short sensory tentacles, and two small dorsal eyes sensitive to light.
    • Scale worms
      • Flattened bodies are covered with broad scales.
      • Some are large, all are carnivores and some are commensals in burrows of other organisms.
    • Fireworms
      • Have hollow, brittle setae that contain poisonous secretions.
      • Feed on cnidarians.
    • Tubeworms
      • Tube-dwellers
      • May line their burrows with mucus
      • Use cilia or mucus to obtain food
    • Fanworms or Featherduster worms
      • Unfurl tentacular crowns to feed.
      • Food moved from radioles to mouth by ciliary action.
    • Parchment Worms
      • Lives in a U-shaped tube.
      • Modified segments pump water through tube.
    • Clade Siboglinidae
      • Formerly members of phylum Pogonophora (beardworms).
      • Discovered in 1900.
      • 150 species described.
      • Most are small, less than 1 mm in diameter.
      • Giant beardworms that live in deepwater hydrothermal vents are 3 m long and 5 cm in diameter.
    • Clade Clitellata
      • Class Oligochaeta and Class Hirudinida
      • Form reproductive structure called a clitellum.
      • Members are derived annelids that lack parapodia.
      • Hermaphroditic (monoecious) animals that exhibit direct development.
    • Class Oligochaeta includes earthworms and many freshwater worms.
      • They possess setae, but not as much as polychaetes.
    • Class Oligochaeta - Reproduction
      • Earthworms are hermaphroditic – male and female organs in the same animal.
      • When mating, two worms are held together by mucus secreted by the clitellum.
    • Class Oligochaeta - Feeding
      • Food is stored in a thin-walled crop.
      • Muscular gizzard grinds food into small pieces.
      • Digestion and absorption occur in intestine.
    • Class Oligochaeta - Nervous System and Sense Organs
      • Pair of cerebral ganglia connect around the pharynx to the ganglia of the ventral nerve cord.
      • Neurosecretory cells in brain and ganglia secrete neurohormones.
    • Class Oligochaeta - General Behavior
      • Avoid bright light (negative phototaxis).
      • Chemical stimuli are important in locating food.
      • Limited learning ability - primarily trial- and-error learning.
    • Class Hirudinea includes the leeches.
      • Primarily freshwater, a few marine & terrestrial.
      • More common in tropical climates.
    • Leeches are hermaphroditic and have a clitellum (only appears during breeding season), like oligochaetes.
    • Chemical stimuli are important in locating food.
    • 10 to 17 pairs of nephridia.
    • Coelomocytes and other special cells may assist in excretion. 
    • 21 pairs of segmental ganglia in between along a double nerve cord.