Chordata 1

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  1. List and describe the 5 major identifying characteristics of the Phylum Chordata

  2. Why are tunicates called that?

  
• Phylum Chordata
• Urochordata and Cephalochordata
• Phylum Chordata


  • Very diverse phylum
  • Most advanced phylum of the animal kingdom
  • More complex anatomy
• Unique combination of 5 characteristics of Phylum Chordata

  • Notochord
  • Pharyngeal slits or pouches
  • Dorsal tubular nerve cord
  • Postanal tail
  • Endostyle or thyroid gland
• Bilaterally symmetrical deuterostomes
• Notochord


  • Flexible rodlike structure enclosed by a fibrous sheath
  • Provides basic support and serves as the main axis for muscle attachments to permit "fishlike" undulatory movements
  • First part of skeleton to form in embryo
  • Remnants remain as "intervertebral discs"
• Pharyngeal slits


  • Openings between the digestive tract and outside of the body
  • May be in form of pouches
  • Filter feeding apparatus or, in some, gills develop for gas exchange
• Dorsal Tubular Nerve Cord

  • The nerve cord is a single dorsal hollow nerve cord
  • Expanded anteriorly into the brain
• Endostyle/Thyroid Gland


  • Ventral aspect of the pharynx
  • Secretes mucus used in filter feeding
  • Transformed into thyroid gland in adult lampreys and other chordates
  • In most chordates, the same tissue has become an endocrine gland in the neck region that helps control metabolism
• Post-Anal Tail


  • Extends posteriorly beyond anal opening
  • Provides motility
  • Specially designed for propulsion in water
• 3 Major Subphyla of Phylum Chordata

  • Urochordata (tunicates)
  • Cephalochordata (lancelets)
  • Vertebrata (vertebrates)
• Subphylum Urochordata (tunicates)


  • All marine
  • Most are bag-like sessile suspension feeders as adults
  • Lack a coelom
  • Pump water through siphons
  • Adults have tough, nonliving, tunic covering body
• Tunicate Metamorphosis


  1. Tadpole-like larva has typical Chordata features

  2. Adults resemble sponges more than they do other chordates, most are sessile

  
• Salps (tunicates)


  • Barrel-shaped pelagic animals
  • Live singly or in colonial chains up to several meters long
• Tunicate Feeding and Digestion

  1. Incurrent siphon -> pharynx (branchial sac) -> slits -> atrium -> excurrent siphon

  2. Uses mucus and cilia to move food toward mouth

  3. The filtered water passes into the atrium and out the excurrent siphon

  4. Digestive waste exits with excurrent water
• Tunicate Respiration


  Pharynx: Gas exchange
• Tunicate Circulation


  • Simple open circulatory system with a small ventral heart and 2 major blood vessels
  • Blood is pumped through the sinuses within the animal's tissues
• Tunicate Nervous System


  Nerve with ganglia and plexus of nerve fibers
• Tunicate Excretion


  • No specialized excretory organs
  • Nitrogen wastes are in the form of crystals deposited in the tunic
• Tunicate Reproduction and Development

  1. All tunicates are hermaphrodites with single ovary and testis

  2. Fertilization produces an elongated free-swimming larva

  3. Tadpole larva has all 5 major chordate characteristics

  4. Swims about for hours to days, until it finds a suitable substrate to settle on

  5. In just 10-15 seconds the tail, notochord, nerve cord, brain sensory structures and muscles are crushed into a mass of tissue

  
• Some believe vertebrates arose from a neotenous tunicate
• Subphylum Cephalochordata (lancelets)


  • Shallow marine substrates
  • Partially buried filter feeders
  • Notochord extends into head
  • Most of the cells are muscle cells
  • Notochord is somewhat contractile
  • Oral hood with cirri
  • Segmentally arranged muscles on either side of notochord

  
• Cephalochordata Maintenance Functions


  • Filter feeding
  • Ciliated gill bars create water currents
  • Cirri sort food
  • Endostyle secretes mucus that traps food on gill bars
  • Transported to gut
  • Circulation: Contractile waves in vessels propel blood
  • Excretion: Excretory tubules receive waste from blood
  • Coelom reduced
• Cephalochordata Reproduction and Development

  1. Dioecious

  2. Gametes shed into atrium and exit via atriopore

  3. External fertilization

  4. Free-swimming larvae settle and metamorphose to adults
• Deuterostomata: Echinodermata, Hemichordata, Chordata
• Molecular, morphological, and developmental evidence point to the chordates as monophyletic
• Third chordate subphylum is Craniata (Infraphylum Vertebrata)


  • Largest and most successful chordates
  • Bony or cartilaginous vertebrae completely or partially replace notochord
  • Three-part brain
  • Skeleton modified into skull or cranium
  • Abundant fossil record