Chp 5

• Protostomia


  A clade of animals, together with deuterostomes they make up the Bilateria (triploblasta), mostly comprising animals with bilateral symmetry and three germ layers
• Protostomes


  • Embryos undergo spiral cleavage and the blastopore becomes the mouth
  • Bilaterally symmetric organisms with a distinctive head region and posterior region specialized for locomotion
  • Have three embryonic tissues, most have a coelom but some are acoelomates or have a pseudocoelom
  • Some have segmented bodies
• Molecular phylogenies support the hypothesis that protostomes are a monophyletic group
• Analyses of DNA sequence data revealed a major branching event within the protostome lineage, creating the groups Lophotrochozoa and Ecdysozoa
• Protostome superphyla


  • Lophotrochozoa
  • Ecdysozoa
• Lophotrochozoa


  • Triploblastic, bilaterally symmetric, show cephalization
  • Includes Trochozoans (with trochophore larvae) and Lophophorates (with lophophore feeding structure)
• Ecdysozoa


  • Possess a cuticle that is periodically molted (ecdysis)
  • Lack motile epidermal cilia, have direct development without a free-living larval stage
• Ecdysozoan phyla


  • Eurarthropoda (chelicerata, crustacea, myriapoda, hexapoda)
  • Tardigrada (water bears)
  • Nematoda (roundworms)
• The Eurarthropoda and Tardigrada have been grouped together as the Panarthropoda due to their segmented body plans
• Ecdysis


  The process of molting the cuticle, controlled hormonally by ecdysteroids
• Many ecdysozoans undergo partial or complete metamorphosis before reaching the adult stage, with larvae that may look very different from the final adult and live in different environments