Introduction to Chordates

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Introduction to Chordates

• BIO 122 Zoology
• Newberry College

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Phylum Chordata

• Most complex of all phyla
• All have a notochordrod-like semirigid body of
  cellsusually extends length of bodyventral to
  nervous systems spine
• Purposes1) support stiffen body2) provide
  skeletal support for muscles

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Phylum Chordata

• Five important features of chordates
• Notochord
• Dorsal tubular nerve cord
• Pharyngeal pouches and gill slits
• Endostyle
• Postanal tail

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Chordate characteristics

• 1) Notochord - a flexible, rod-like structure
  beginning of the internal skeleton axis for
  muscle attachment, flexible w/o shortening
  in vertebrates the notochord becomes segmented
  as vertebrae

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Chordate characteristics

• 2) Dorsal Tubular Nerve Cord - produced by
  infolding of ectoderm during early development
  in many invertebrates the nerve cord is
  ventral and solid in many anterior end becomes
  swollen brain

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Chordate characteristics

• 3) Pharyngeal Pouches and Gill Slits - perforated
  openings lead from pharyngeal cavity to outside
  body in simplest aquatic chordates it allows
  for suspension feeding in terrestrial
  organisms is only developmental

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Chordate characteristics

• 4) Endostyle - or its derivative, the thyroid
  gland in the simplest chordates the endostyle
  secretes mucus that traps small food particles

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Chordate characteristics

• 5) Postanal Tail - extension of body beyond
  anus enhances ability for movement (aquatic)
  balance (terrestrial)

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Additional Chordate Features

• Development pattern as in Echinoderms radial,
  indeterminate cleavage deuterostome
  enterocoelous
• Segmented muscles in an unsegmented body
• Complete digestive system
• Closed circulatory system
• Endoskeleton made of cartilage and/or bone

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Classification of Chordates

• Three distinct SubphylaUrochordata
  tunicatesCephalochordata lanceletsVertebrata
  - vertebrates

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Subphyla of Chordates

• SUBPHYLUM UROCHORDATA - tunicates
• Only larval form moves, adults are sessilelarvae
  with all chordate characteristics
• Adults relatively small, up to a few cm long
  produce a leathery outer surface ( tunic) loss
  of notochord tail, nerve cord greatly reduced
  become filter feeders with siphons gills slits
  become net-like to trap food
• Individuals are hermaphroditic reproductive
  cells into water, external fertilization

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Diagramatic tunicate
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Subphyla of Chordates

• SUBPHYLUM CEPHALOCHORDATA - lancelets
• Slender, lancet-shaped, 5-7 cm long sandy
  bottoms of shallow marine environments
• Adults clearly with all the chordate
  characteristics suspension feeders, trap food
  in gills slits circulatory system closed, but
  no distinct heart no obvious brain
• Separate males and females fertilization
  external

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Diagramatic lancelet
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Subphyla of Chordates

• SUBPHYLUM VERTEBRATA - vertebrates
• Very large and diverse groupwell known due to
  large size
• Not all chordatefeatures in adults

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Characteristics of Vertebrates

1. Expanded endoskeleton - living endoskeleton
   internal skeleton, grows with the organism
   commonly is hollow, provides support
   distinctive covering around brain cranium

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Characteristics of Vertebrates

• Gills in pharynx - better respiration other
  subphyla use slits for filter feeding more
  active aquatic vertebrates developed gills
  with muscles heart developed to enhance
  circulation

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Characteristics of Vertebrates

1. Enhanced Nervous System with anterior
   swelling more complex behaviors of swimmers
   predators has tripartite brain (fore-, mid-
   and hind-brain) development of enhanced senses

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Characteristics of Vertebrates

1. Development of neural crest ectodermal placode
   enhances complexity neural crest enhances
   development of skeleton, tooth dentine
   endocrine glands ectodermal placodes enhance
   sensory development (olfactory, eye, ear)

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CLASSIFICATION OF VERTEBRATES

• Several important characteristics to separate1)
  skeleton jaw composition cartilage or bony2)
  number structure of paired appendages3) dermal
  covering over body4) relative number of gill
  slits of an adult5) type of covering over egg

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CLASSIFICATION OF VERTEBRATES

• SUPERCLASS AGNATHA lampreys hagfishcartilagino
  us skeleton and no jawno paired appendagesskin
  smooth (slimy)about 7 gill slits per sideeggs
  with gelatinous covering (aquatic)heart
  2-chambered (1 atrium 1 ventricle)

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SUPERCLASS AGNATHA

• Lamprey (note gill slits)

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CLASSIFICATION OF VERTEBRATES

• SUPERCLASS GNATHOSTOMATA All other vertebrates
  with jaws paired appendages

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CLASSIFICATION OF VERTEBRATES

• Class Chondrichthyes (sharks rays)
• cartilaginous skeleton and jaw present
• 2 pair fins
• placoid scales (tooth like with root)
• 5-7 pair gill slits
• eggs with gelatinous covering (aquatic)

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CLASSIFICATION OF VERTEBRATES

• Class Actinopterygii (bony ray-finned fish)
• bony skeleton, jaw present
• 2 paired appendages fins
• overlapping dermal scales (typically thin
  flexible)
• gill slits with covering operculum
• egg covering gelatinous

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CLASSIFICATION OF VERTEBRATES

• Class Amphibia (amphibians)
• bony skeleton, jaw present
• 2 paired appendages, legs
• smooth skin
• gills only in juvenile forms
• eggs with gelatinous covering (aquatic)

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CLASSIFICATION OF VERTEBRATES

• Class Reptilia (reptiles)
• bony skeleton, jaw present
• 2 paired appendages, legs
• hard scales (snakes) or plates (turtles)
• gills embryonic only
• eggs with leathery covering (terrestrial)

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CLASSIFICATION OF VERTEBRATES

• Class Aves (birds)
• bony skeleton, jaw present
• 2 paired appendages legs wings
• feathers scales on legs
• gills embryonic only
• eggs with calcified shell (terrestrial)

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CLASSIFICATION OF VERTEBRATES

• Class Mammalia (mammals)
• bony skeleton, jaw present
• 2 paired appendages legs ( arms)
• fur and/or hair
• gills embryonic only
• viviparous (few with calcified shells)