EVOLUTION QUESTION 1990:			L. PETERSON/AP BIOLOGY

	A.  Describe the differences between the terms in each of the following pairs.
		(1)  Coelomate versus  acoelomate body plan
		(2)  Protostome versus  deuterostome development
		(3)  Radial versus  bilateral symmetry
	B.  Explain how each of these pairs of features was important in constructing 
	       the phylogenetic tree shown below. Use specific examples from the tree 
      	       in your discussion.

  
  
  
                         Chordata
  
                                        Arthropoda
                                             Annelida
  
          Echinodermata                           Mollusca
  
  
                                           Nematoda
  
                                             Rotifera
  
                                                 Platyhelminthes
  
               Cnidaria
  
  
                              Porifera
  STANDARDS:
  
  A. (1)  COELOMATE VS. ACOELOMATE
  
  1 -  Coelomate: internal body cavity lined with mesoderm
          (not sufficient to say: "true body cavity")
  1 -  Acoelomate: lacking internal cavities altogether or having:
               a pseudocoelom (Nematoda and Rotifera)
               a spongocoel (Porifera)
               mesoglea (Cnidaria)
               a solid layer of mesoderm (Platyhelminthes)
  [Max. = 2 / must define both for full credit]
  
       (2)  PROTOSTOME VS. DEUTEROSTOME DEVELOPMENT
  
  1 - Protostome: mouth develops near/at the blastopore or anus forms secondarily (later),
         OR featuring:   spiral cleavage (micromeres between macromeres);
               determinate/mosaic development (blastomere fate is 
               established at very early stages of development);
               mesoderm from cells that migrate into the blastocoel 
               near blastopore schizocoelous coelomation (internal split 
               in solid wedge of mesoderm that is independent of gut);
               trochophore larva;
  1 - Deuterostome: anus develops near/at the blastopore or the mouth forms secondarily (later),
         OR featuring:   radial cleavage (micromeres directly above macromeres);
               indeterminate/regulative development (blastopore fate is 
               variable and not established until late in development);
               mesoderm arises from outpocketings of the gut;
               enterocoelous coelomation (outpocketings of gut);
               dipleurula larva
  [Max. = 2 / must define both for full credit]
  
      (3) RADIAL VS. BILATERAL SYMMETRY
  1 - Radial: several planes passing through the long or central axis can divide the 
         organism into similar parts.
  1 - Bilateral: (only) one plane passing through the long axis divides the organism 
         into similar right and left sides -- exhibits cephalization.
  1 - Echinoderms: bilaterally symmetrical larvae, but appear to have radially 
         symmetrical adult forms.
  [Max. = 2]
  
  B.  PHYLOGENETIC TREE
  1 - for examples of contrasting pairs (phyla or organisms) using terms from above;
         answer here or in part A.
  1 - for using above terms in explanation of why phyla are in separate groups 
         (or separate branches) of the tree.
  
  1/1 -  Body symmetry (cephalization) permits separation of Porifera and Cnidaria
     (radially symmetrical) from other phyla (bilaterally symmetrical).
  1/1 -  Coelomation permits separation of Platyhelminthes, Nematoda, and Rotifera 
              from other phyla above Cnidaria: flatworms are acoelomate, whereas those 
              other than nematodes and rotifers are coelomate.
  1/1 -  Origin of the mouth and anus permit separation of Echinodermata and Chordata
     (deuterostomes) from Arthropoda, Annelida, and Mollusca (protostomes).
  
     [Some include Platyhelminthes, Nematodes, and Rotifers as protostomes.]
  1 - Nematodes and rotifers are grouped separately because both are pseudocoelomate.
  1 - Phylogenetic trees based taxonomic relationships on homologous structures,
         patterns of embryonic development, and common ancestry.
  [Max. = 6]