Invertebrates 6

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Invertebrates 6

• Phylum Echinodermata

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Phylum EchinodermataSpiny-skinned
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Evolutionary relationships
and HOX genes
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Echinodermata 4 key features

• Calcareous internal skeleton
• Parts Plates, spines and pedicellariae
• Why considered internal?
• Water vascular system (controls tube feet)
• Derived from coelom
• Layout
• Tube foot control
• Other functions
• Symmetry
• Bilateral symmetry (larvae)
• Pentamerous radial symmetry (adults)
• Mutable connective tissue

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Body plan Other aspects

• Perivisceral coelom
• Houses organs
• Gas exchange
• Hydrostatic skeleton
• Digestive system
• Can be highly branched
• Complete (generally)
• Nervous system
• No brain
• Branches parallel water vascular system
• Sensory (sea stars)
• Eye spots
• Receptors associated with tube feet
• No circulatory system
• No excretory system

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Class Asteroidea sea stars

• Feeding
• Respiration
• Protection

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Class EchinoideaSea urchins and others

• Feeding
• Respiration
• Protection

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Class HolothuroideaSea cucumbers
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Class OphioroideaBrittle stars, basket stars

• Feeding
• Respiration
• Protection

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Class CrinoideaSea lilies
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Chordates!

• Subphylum Urochordata
• Subphylum Cephalochordata
• Subphylum Vertebrata (focus)

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Evolutionary relationships
and HOX genes
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Phylum Chordata 4 key featuresEach appears
in a least one life stage
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Phylum Chordata 4 key featuresEach appears
in a least one life stage

• 1) Notochord
• Longitudinal flexible rod made of fluid-filled
  cells in fibrous tissue
• Dorsal
• Underlies nerve cord
• Replaced by jointed vertebral column in the
  vertebrates

• 2) Dorsal, Hollow Nerve Cord
• Derived from ectoderm
• Develops into central nervous system
  (brain/spinal cord)

• 3) Pharyngeal Gill Slits
• Slits in pharynx allowing for water efflux
• Multiple functions in vertebrates (e.g. feeding
  in tunicates, gills in fish)

• 4) Muscular, Post-anal Tail
• Skeletal elements / muscle for mobility

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Subphylum Urochordata the tunicates

• Invertebrates (notochord but no vertebral column)
• Larva has all five chordate features
• Adults retain only the pharyngeal slits
• Expanded pharynx works similarly to the ctenidium
  of a mussel

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Subphylum Cephalochordata the lancelets

• Invertebrates (notochord but no vertebral column)
• Larva has all five chordate features
• Adults retain all chordate features
• Neoteny (paedogenesis) of a urochordate-like
  larva?
• Muscles develop from somites Blocks of mesoderm
  (segmented)
• Feed similarly to the Urochordata