25.1 Animal Origins What is an animal? • Multicelled, heterotroph • Most motile • Reproduce sexually • Unwalled • Most have tissue and organs
Jan 01, 2016
25.1 Animal Origins
What is an animal?• Multicelled,
heterotroph
• Most motile
• Reproduce sexually
• Unwalled
• Most have tissue and organs
Tissues
Key innovation in complexity:• Ability to interact in
functional units Epithelium
• Sheet like array
• Functions: absorption, secretion, sensory
• 1st epidermis
• 2nd gastrodermis
cont.
Connective tissue• All contain
• Most have a matrix in which living cells and protein fibers (collagen) exist
Embryo forming – 2 primary tissue layers• Outer ectoderm
• Inner endoderm
• mesoderm
Body Size
How to deal with increasing constraints of SA-V ratios of cells?• Pseudopds and microvilli in single cell species
• Simple animals are sheets/ribbons
• circulatory system in large animals
Where did it all start?
Colonial Theory • 1st animals evolved
from tiny colony of flagellated, amoeba like cells
• Choanoflagellates Share common
ancestor with sponges
25.2 Basic Body Plans
Body Symmetry• Polarity – front to
back axis, with anterior and posterior ends
• Radial – organized around main axis, water
Gut and Body Cavity
Incomplete gut• Sac-like
• One opening
• 1st to evolve
Complete gut• Tubular
• 2 openings
• Mouth (specialized feeding structures) to anus
Formation of Complete Gut
Protostomes• 1st opening
becomes mouth
• Flatworms, mollusks, annelids, roundworms, arthropods
Deuterostomes• 1st opening
becomes anus
• Echinoderms, chordates
epidermis gutcavity
organs packed betweengut and body wall
No coelom(acoelomateanimals)
Fig. 25-6a, p.406
None – flatworms, few invertebrates• Tissue and organs fill
region between gut and body wall
epidermis
gutcavity
unlined body cavity around gut
Pseudocoel(pseudocoelomateanimals)
Fig. 25-6b, p.406
Pseudocoel – roundworms• In some protostomes coelom is reduced/lost
epidermis
gutcavity
peritoneumbody cavity with lining thatholds internal organs in place
Coelom(coelomateanimals)
Fig. 25-6c, p.406
Repeating Units
Favors regional specialization in structure and function
Segmentation – annelids, arthropods, vertebrates• Divide into a series of functionally connected units
along main body axis
Phylum Examples Evolutionary Milestone
Porifera sponges multicellularity
Cnidaria jellyfish, hydra, coral tissues
Platyhelminthes flatworms bilateral symmetry
Nematoda roundworms pseudocoelom
Mollusca clams, squids, snails coelom
Annalida earthworms, leeches segmentation
Arthropoda insects, spiders, crustaceans jointed appendages
Echinodermata starfish deuterostomes
Chordata vertebrates notochord