BI113 Lecture 24

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BI-113 Lecture 24

• Deuterostomes

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The other branch of the tree

• Deuterostomes
• Radial, indeterminate cleavage exhibited by early
  embryo
• Coelom forms by enterocoely
• Blastopore forms the anus

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Star light . . . Star bright, but . . .

• Phylum Echinodermata
• Seastars, brittle stars, sea urchins, sand
  dollars, and sea cucumbers
• 7,000 species
• Marine
• Sessile or slow-moving creatures
• Superficial radial body form (which is
  secondarily derived from bilateral morphology)
• Body plan is in multiples of 5

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. . . dont call me Starfish

• Endoskeleton of calcareous plates with thin layer
  of skin over the top
• The skin has dermal gills, which serve as
  respiratory structures
• Water vascular system
• Series of paired bulbs (ampullae) with ventral
  extensions - tube feet
• Madreporite
• Water sieve on dorsal surface that serves as
  incurrent pore for network of tubes
• Ring canal and radial canals extend into arms of
  seastars

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Sea star anatomy
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Water vascular system
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Reproduction in echinoderms
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Echinoderm diversity
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Chordates
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Phylum Chordata

• the Chordates
• 50,000 species
• Chordate characteristics
• These are all seen at some time during the life
  cycle
• Many may only be seen in larval stages of some of
  the lower chordate groups

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Chordate characters

• Notochord
• Cartilaginous rod for body support
• Dorsal, hollow nerve cord
• Brain and spinal cord with fluid-filled space
• CNS formed from embryonic tissue layer
• Neuroectoderm
• Induced to form by the underlying notochord

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Chordate characters (cont.)

• Pharyngeal gill slits
• Primitively, the pharyngeal slits serve as
  filter-feeding structure
• Later modified as gas exchange structures (gills)
• Then as other structures
• Eustachian tube, parathyroid and thymus glands
• Post-anal tail
• Muscular tail that extends beyond the anus
• Used for swimming in many species

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Chordate characteristics
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In addition, chordates exhibit . . .

• Strong cephalization
• Bilateral symmetry
• An internal support system
• Endoskeleton allows for continued, uninterrupted
  growth (as opposed to the situation in arthropods
  that must go through the molting process to
  replace the exoskeleton)

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Four major chordate groups

• Subphylum Hemichordata
• Subphylum Urochordata
• Subphylum Cephalochordata
• Subphylum Vertebrata

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Subphylum Hemichordata

• the Acorn worms
• 75 species
• Burrowing, marine lower chordate
• Filter feeders

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Chordate phylogeny
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Subphylum Urochordata

• the Tunicates or sea squirts
• 2,500 species
• Sessile as adults
• With reduced chordate characters
• Pharyngeal basket serves as filter-feeding
  structure
• Motile as larvae

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Sea squirt
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Urochordata
tadpole larva
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Subphylum Cephalochordata

• the Lancelets
• Amphioxus - Branchiostoma
• 25 species of marine, sediment-dwelling filter
  feeders
• This group is especially important because they
  seem to represent an evolutionary connection to
  the jawless vertebrates

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Cephalochordates
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Amphioxus
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Deuterostome phylogeny