Ch 33 Animal Diversity/Body Plans

Question 0

Bilaterians

Answer 0

• Mitotic cell divisions of egg form 
  hollow ball of cells called blastula
• Blastula indents to form 2-layer thick 
  ball with:
    – Blastopore: opening to outside
    – Archenteron: primitive body cav

Question 1

Body cavity

Answer 1

• Acoelomates:
No body cavity

• Psuedocoelomates:
Body cavity bet. mesoderm &
endoderm

• Coelomates:
Body cavity within mesoderm

Question 2

Protostomes

Answer 2

• Develop mouth 1st from or near 
  blastopore
• Anus (if present) develops from 
  blastopore or other region of embryo
• Spiral cleavage in embryonic cells

Developmental fate of cells
• Determinate development
• Tissue type determined early

Question 3

Deuterostomes

Answer 3

• Develop anus 1st from blastopore
• Mouth develops later from other
region of embryo
• Radial cleavage in embryonic cells

Developmental of cells
• Indeterminate development
• Division early zygote prod identical 
  daughter cells
     – Tissue type is determined later
• How identical twins can form early on

Question 4

Advantages of segmentation

Answer 4

1) Allows redundant organ systems in
adults (occurs in the annelids)

2) Allows more efficient/flexible
movement b/c each segment
moves independently

Question 5

Traditional classification of animals

Answer 5

Metazoans (multicellular animals) divided into 36 phyla based on shared anatomy and embryology

• Parazoa: lack symmetry & tissues
• Eumetazoa: have symmetry & tissue
• Triploblastic: Have 3 germ layers

Question 6

Porifera (Parazoa)

Answer 6

• Lacking tissues (and therefore
organs) and a definite symmetry
• Various growth forms

Cell types
• Truly multicellular
• 3 functional layers in “vase”

Question 7

The 3 functional layers in Parazoa (sponges)

Answer 7

1) Outer epithelium
• Water comes in ostia, exits osculum

2) Mesohyl
   • Mid layer: gelatinous matrix
   • Spicules: needles of calcium 
      carbonate
   • Spongin: reinforce tough protein 
      fibers

3) Choanocytes:
   • Collar cells
   • Flagellated: contributes to water 
      circulation
   • Face internal cavity
   • Ingulf/digest food from passing
      water

Question 8

Eumetazoa

Answer 8

• Distinct tissues
• Embryos have distinct layers
   – Inner endoderm forms 
      gastrodermis
   – Outer ectoderm forms epidermis
      & nervous system
   – Middle mesoderm (only in bilateral 
       animals) forms muscles
• True body symmetry
   – Radial or bilateral

Question 9

Phylum Cnidaria

Answer 9

• Most Marine, few freshwater species
• Diploblastic
• Distinct tissues but no organs
    – No rep, circ or excretory systems
• No concentrated nervous system
   – Latticework of nerve cells
   – Touch, gravity, light receptors
• Use nematocysts to capture 
   – Secreted within nematocyte
   – Discharge mechanism unknown
   – Some carry venom

Question 10

Cnidaria body forms

Answer 10

• Polyps: Cylindrical and sessile
• Medusa: Umbrella shape & free living

• Body plan has single opening leading 
  to gastrovascular cavity
   – Site of digestion
   – Most gas exchange
   – Waste discharge
   – Formation of gametes in many

• 2 layered body wall
(1) Epidermis
(2)Gastrodermis
– Mesoglea between layers

• Gastrovascular space also serves as 
   hydrostatic skeleton
    – Provides rigid struct for muscles
       to operate against
    – Gives animal shape
• Many polyp species build
  exoskeleton of chitin or calcium
  carbonate around themselves
    – Some build an internal skeleton

Question 11

Cnidarian life cycle

Answer 11

• Some only as polyps, & others only 
  as medusa, but many alternate 
  between these two phases
      –Both have diploid individuals
• Generally, in species w/ both polyp
   & Medusa in lifecycle, Medusa
   forms gametes
    – Sexes separate
    – Gonochorism: is either male or 
        female
    – Zygote develops into planktonic 
       planula
    – Metamorphosis into polyp
    – Polyp produces Medusa or other 
        polyps asexually.

Question 12

Cnetophora

Answer 12

• 8 rows of comblike plates of fused 
  cilia that bear in coordinated fashion. 
• Many bioluminescent
• 2 tentacles covered w/ calloblasts
    – discharge strong adhesive to 
       capture 
• Phylogenetic position unclear