lesser deuterostome phyla and phylum chordata through agnathans l.
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Lesser Deuterostome Phyla and Phylum Chordata(through agnathans). Contents. Phylum: Chaetognatha Phylum: Hemichordata Phylum: Chordata Subphylum: Urochordata Subphylum: Cephalochordata Subphylum: Vertebrata (Craniata) Superclass Agnatha Class: Myxini Class: Cephalaspidomorphi.

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  • Phylum: Chaetognatha
  • Phylum: Hemichordata
  • Phylum: Chordata
    • Subphylum: Urochordata
    • Subphylum: Cephalochordata
    • Subphylum: Vertebrata (Craniata)
      • Superclass Agnatha
        • Class: Myxini
        • Class: Cephalaspidomorphi
phylum chaetognatha
Phylum Chaetognatha
  • Arrow worms
    • Stratified skin along sides of body.
phylum hemichordata
Phylum Hemichordata
  • Acorn worm
    • Proboscis, collar and trunk
    • Like Chordata
      • Gill slits and a hollow, dorsal nerve chord
      • Have stomochord rather than a notochord
    • Like Echinodermata
      • Tornaria larva resembles bipinnaria larva of echinoderms.
      • Coelomic pouches
      • Nerve plexus
phylum chordata


Phylum Chordata



  • Notochord
  • Dorsal tubular nerve cord
  • Pharyngeal gill slits (pouches)
  • Post anal tail
  • Ventral heart
subphylum urochordata


Subphylum Urochordata
  • Tunicates (sea squirts)
    • Larva has all chordate characteristics
    • Adult sessile, encased in tunic
    • Ventral heart with a large vessel on each side. Heart pumps blood through one vessel—, stops, then pumps blood through other vessel.
    • Endostyle present
subphylum cephalochordata


Subphylum Cephalochordata
  • Branchiostoma -the lancelets or Amphioxus
    • Retain all the chordate characteristics throughout life.
    • Shows the basic diagnostic chordate characteristics very clearly.
    • Also possesses several features that suggest the vertebrate plan
    • Endostyle present
subphylum vertebrata


Subphylum Vertebrata



  • Chordate characteristics present at some stage of life cycle.
  • Integumentary - with stratified epidermis and an inner dermis present.
  • Skeletal -Notochord at least partly replaced by vertebrae. A cranium present.
  • Nervous- 10 to 12 pairs of cranial nerves
  • Excretory - vertebrate kidney (at least mesonephric in adults)
class myxini
Class: Myxini


  • Hagfishes
    • Naked skin containing slime glands
    • No paired appendages
    • No jaws
    • Notochord and other chordate characters persistent
    • Systems
    • Representative pictures
myxini systems


Myxini systems
  • Systems
    • Circulatory - Two chambered heart with aortic arches in gill region have accessory hearts in caudal region.
    • Excretory - pronephric with independent mesonephric kidney posteriorly, isosmotic to sea water.
    • Respiratory - 5 to 16 pairs of gills (one pair or more gill openings)
    • Digestive -complete, with no jawsor stomach present
    • Nervous- they have 10 pair of cranial nerves, no cerebellum. Dorsal and ventral nerve roots united.
    • Integumentary- No scales, skin with slime glands
    • Skeletal - cartilaginous with persistent notochord.
    • Reproductive - both male and female gonads found in some animals, but one one gonad is functional. No larval stage. Life cycle largely unknown
    • Endocrine - pineal gland present, there are islets of pancreas cells around the bile duct
    • Muscle - myomeres alternate
myxini representatives


Myxini representatives

Ventral view

Lateral view

class cephalaspidomorphi
Class: Cephalaspidomorphi


  • Lampreys
    • Slender eel-like body without scales
    • No paired appendages
    • Cartilaginous skeleton, notochord persistent
    • No jaws—Sucker-like oral disc, has teeth and tongue.
    • Ammocoete larvae
    • Systems
    • Representative pictures
lamprey systems


Lamprey Systems
  • Integumentary- No scales , stratified skin
  • Skeletal- Cartilaginous, notochord persistent, no paired appendages.
  • Circulatory- Two chambered heart, aortic arches in gill region.
  • Respiratory - seven pairs of gills each with and external opening.
  • Excretory- Mesonephric kidney, hypotonic sea water, have to osmotically and ionic regulate.
  • Nervous- 10 pairs of cranial nerves, dorsal and ventral nerve roots separated, small cerebellum present.
  • Endocrine- pineal structure, pituitary body present, endostyle present in larvae is thyroid gland present in adult.
  • Muscle - short segmental muscles as in other fishes
  • Digestive-complete, no stomach, liver does not have a bile duct, pancreas cluster of cells near liver.
  • Reproductive - dioecious, larvae= Ammocoete, look much like amphioxus, are freshwater filter feeders.
cephalaspidomorphi examples

Ammocoete larvae

Juvenal lampreys

Adult lamprey mouth with tongue and teeth

Adult lamprey - lateral view


Cephalaspidomorphi examples