Vertebrate Story 3a

Cards (21)

  • Hemichordata
    • Tripart body (3 parts) - proboscis, collar and trunk
    • characters similar to chordates - dorsal nerve cord(deuterostomes) (not hollow) and ventral nerve cord as well (protostomes) and stomachord (endoderm, not homologous)
    • Homologous with chordates - pharyngeal slits, iodine sequestering in pharynx, some with post anal tail in juveniles
    A) trunk
    B) proboscis
    C) mouth
    D) collar
  • Enteropneusta (Acorn worm)
    • Benthic filter feeders using cilia to generate feeding current and mucus to trap food particles
    • Dorsal mucus = ventral ejection? connection? collection?
    • Mucus generated dorsally in the pharynx food collects ventrally
  • Pterobranchia (feather ones)
    • colonial filter feeders with collar modified into ciliated tentacles
    • not in the phylum chordata because only a few of the chordate synapomorphies certain ----
    • pharyngeal slits
    • iodine sequestering cells
    • post anal tail
  • Chordates are upside down hemichordates
  • Chordate body plan
  • Chordate body plan... continued
    • at some point in their life all chordates have 4 basic characteristics (shared and derived)
    • dorsal nerve chord (hollow)
    • Notochord
    • Pharyngeal slits
    • Muscular post anal tail
  • Chordate body plan .... continued
    • Notochord - a hydrostatic organ with fluid filled cells/ spaces contained in a fibrous sheath. Segmented muscles act on notochord to produce undulating motion>
    • Fibrous tube, loosely packed, fluid filled, allows for undulating swimming
  • Chordate body plan ... continued
    • Dorsal hollow nerve cord - as opposed to ventral in protostomes
    • Hollow due to unique ontogeny (origin) forms brain and spinal cord
    • develops from a plate of dorsal ectoderm that invaginates into a tube
  • Chordate body plan ... continued
    • Pharyngeal slits - openings from the pharynx to the body wall
    • filter feeding in protochordates, lated used for respiration in most vertebrates
    • homologous
  • Chordate body plan ... continued
    • muscualar postanal tail - with notochord and segmented musclture, provides very effective propulsion
  • Chordate body plan ... continued
    • endostyle - tissue along pharynx that accumulates iodine.
    • Mucus production in non vertebrates, hormonal in most vertebrates (thyroid)
    • ventral surface makes mucus
    • chordates are upside down hemichordates
  • Chordate body plan ... continued
    • pharyngeal pouch
  • Urochordata
    • Known as the sea squirts or tunicates
    • tunics are the only animals able to synthesise cellulose like plants
    • They have concentrate vadium in their blood cells - thought to be used of respiration?
    • Tadpole larval stage that disperses and most with distinct adult stage
    • all chordate characters apparent in larval stage
    • Ventral endostyle generates mucus and food collects dorsally
  • Urochordata: Ascidiacea (200 species)
    • Sessile
    • can be solitary or colonial
    • Hermaphrodites
    • Metamorphosis tadpole larvae short lasting
  • Urochordata: Larvacea (70 species)
    • Planktonic
    • adults retain some larval features - might be derived from ascidian larval forms
    • all species except 1 monoecious but protandrous
    • Live in a secreted mucus house
    • exceptional filter feeders (can eat bacteria)
  • Urochordata: Thaliacea (70 species)
    • free living, planktonic
    • derived from ascidians
    • Jet propulsion using feeding current - excurrent and incurrent on opposite sides of body and used for propulsion
  • Cephalochordata
    • Pikaia - an early cephalochordate from the burgess shale (good for preservation) in alberta (Middle cambrian) (114 specimens)
    • These fossils may have had a brain because there was evidence of swelling in the nerve cord
    • They also had tentacles which is not usually seen
  • Cephalochordata: Yunnanozoon
    • from the lower cambrian of China, might have been an early vertebrate
    • This was the beginning of multicellular animals in this time frame
  • Cephalochordata
    • Adults very closely match the basic chordate body plan, but no distinct brain, eyes or neural crest tissue.
    • Filter feeders most sessile unless they are disturbed (burrow into the sand and chill waiting for food)
    • they filter feed in a similar manner to urochordates with an atrium developed from metapleural folds and atriopore find and fin rays but on homologous to those in fishes
    • Caecum/ hapatic diverticulitum - precursor to liver and pancreas
  • Cephalochordata contd
    • Laravel with simple mouth and exposed pharyngeal slits
    • metapleural folds encase the pharyngeal region to create an atrium and mouth parts at metamorphosis
    • Unusual development of pharynx - develops 1 side first then wraps around
  • Garstangs Auricularian hypothesis was influential
    • he thought the post anal tail was cool because the tunicates look the same in adult vs larvae but the larvae has a tail
    • See slides 27,28,29 of 3a