Deuterostome Phyla

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Deuterostome Phyla
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Deuterostomes

• Informal group of animal phyla
• Kingdom Animalia
• subkingdom Deuterostomes
• Phylum Chordata
• Phylum Echinodermata
• subkingdom Protostomes (later)

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Deuterostomes

• Two major phyla share two embryonic characters
• Anus develops at site of blastopore (2nd mouth)
• Mesoderm develops from lateral pouches of
  endoderm
• gut-pouch coelom

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Deuterostomes

• Mesoderm develops from lateral pouches of
  endoderm
• Pouches of endoderm bulge, pinch off to form
  Mesoderm (3rd germ layer) and gut pouch
  coelom.
• Cavity enclosed in mesoderm coelom
• Coelom body cavity completely enclosed by
  mesoderm not opening to outside.

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Deuterostomes

• Phylum Chordata
• Subphylum Vertebrata
• Subphylum Urochordata ( tunicates)
• Subphylum Cephalochordata ( lancelets)

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Deuterostomes

• Phylum Echinodermata (Gr. spiny skin)
• Actually, skeleton is spiny.
• Marine only, largest phylum with no aquatic or
  terrestrial members.
• Pentaradial symmetry (NOT radial)
• Endoskeleton of ossicles
• Water vascular system

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Phylum Echinodermata

• Pentaradial symmetry (NOT radial)
• 5-sided or 5-part symmetry around an axis
• Adaptation to sessile or slow-moving life
• Arrays sense organs defenses all around body
• Larvae are bilaterally symmetrical

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Phylum Echinodermata

• Why pentaradial?
• Lots of hypotheses, few with much support.
• Extinct, fossil echinoderms known with 3-, 4-,
  and 6-radial symmetries.

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Phylum Echinodermata

• Endoskeleton of ossicles
• CaCO3, calcium carbonate
• Echinoderms have left abundant fossils.

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Phylum Echinodermata

• Water vascular system
• For circulation, respiration, locomotion feeding

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Phylum Echinodermata

• How tube feet work
• Transfer water between ampulla podium
• Muscles bend, attach, pull
• Suction cup at end
• Nervous system coordinates hundreds of tube feet.

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Phylum Echinodermata

• Class Crinoids
• Class Sea Stars
• Class Brittle Stars
• Class Sea Urchins
• Class Sea Cucumbers

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Class Crinoids

• Most similar to ancestral echinoderms
• Small body with many branched arms
• Mouth (oral side) tube feet up
• Feed on organic detritus falling on arms, push
  food to mouth.

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Class Sea Stars

• Five body extensions (not arms)
• Digestive glands, gonads in extensions
• Eversible stomach
• Predators on clams, barnacles, etc.
• Oral side down, walk on tube feet.

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Class Brittle Stars

• Body disc
• Thin, flexible arms

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Class Sea Urchins

• Spherical body (flattened in sand dollars)
• Prominent spines
• Herbivores

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Class Sea Cucumbers

• Ossicles small, reduced
• Soft-bodied
• Worm-like with 5 rows of tube feet
• Some rows vestigial
• Oral tentacles
• Feed on organic detritus