Vertebrate Story 3a

• 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