Introduction to Invertebrates

1. Shared Animal Characteristics
Multicellular
 Most have tissues and organs
Aerobic heterotrophs
Reproduce sexually
Develop from embryos
Motile
Today we will focus on invertebrates
 No internal backbone
Compare similarities and differences through
several basic features

2. Symmetry
Radial symmetry:
body parts arranged
around a central axis
Bilateral symmetry:
have a front and back
end and right and left
side

3. Embryo Tissue Layers
Zygote develops into a mass of cells
Primary tissue layers form
 Simple radial animals have two layers
 Outer ectoderm
 Inner endoderm
 Bilateral animals have a third layer, mesoderm in the middle

4. Pattern of Development
Protostome: first embryo opening becomes the
mouth
 Examples: flatworms, molluscs, roundworms, arthropods
Deuterostome: second embryo opening becomes
the mouth
 Example: Echinoderms, chordates

5. Body cavity: Coelom
Cavity between the gut and the wall that is lined with
tissue
 Cushions organs
 Helps organs grow and move independently
3 types of body cavities

6. Acoelomate: no body
cavity
 Flatworms
Pseudocoelmate:
false cavity
 Partially lined
 Roundworms
Coelomate: true
cavity
Higher animals

7. Animal Phylogenetic tree

8. Sponges: Phylum Porifera
No true tissues
No germ layers
Acoelomates
No symmetry
Sessile adult
Asexual and sexual reproduction
Spicules: made of different substances; for protection
Collar cells (choanocytes)-flagellated, create water
currents
Amoebocytes-digestion, secretion
Epidermal cells-cover surface
Osculum: largest opening for water

9. Grantia slide

10. Jellyfish Phylum Cnidaria
Radial Symmetry
Two germ layers
Simple tissues
Acoelomates
Polyp and/or medusa stage
Stinging cells—Cnidocytes with nematocysts
 Fluid filled capsule with thread
Nerve net

11. Hydra-cnidarian example
Look at slides and live specimens

12. Roundworms: Phylum Nematoda
Bilateral symmetry
Three germ layers
Molt their cuticle
Pseudocoelomates
Cephalization with brain
Complete digestive system (2 openings)
Many parasites

13. Roundworm examples
Ascaris: intestinal parasite, infects humans
Trichinella: encysts in human muscles causing
trichinosis
Vinegar eels: live specimen

14. Three germ layers
Coelomates
Bilaterally symmetrical
Jointed appendages
Exoskeleton with chitin
Specialized segments
Cephalization
Phylum Arthropoda

15. Arthropod Lineages
Trilobites (all extinct)
Crustaceans (crabs, shrimps, barnacles)
Chelicerates (spiders, mites, scorpions)
Uniramians (insects, centipedes, millipedes)
Today: dissect a crayfish

17. Wear goggles, gloves, and lab coats
Carosafe safety procedures
Put specimens in correct containers
 No gloves or paper towels with tissue waste
No unauthorized dissections-please treat specimens
with respect
Clean all dissection equipment at conclusion
Important Dissection Notes