Unit III: Intro to Metazoa Flashcards
What are the 4 Tree of Life branches of Metazoa (Animalia)?
- Ctenophora
- Porifera
- Cnidaria
- Bilateral
What are Metazoa characteristics?
- All are multicellular heterotrophs
- All animals move under their own power at some point in their life cycle
- Variety of tissue types (except sponges, all have neurons & muscle cells that lack cell walls)
How do the Metazoa reproduce?
- Most species have sexual reproduction (production of haploid gametes to fertilization)
- Some species area capable of asexual reproduction (budding an outgrowth of the body or unfertilized eggs)
What are the steps of Metazoa development?
- Development begins with the cleavage
- Formation of (typically hollow) blastula
- Gastrulation
Cleavage
cell divisions subdividing a fertilized egg (zygote) to form a multicellular embryo
Blastula
16-32 cell stage of development of an animal
Gastrulation
process in which the blastula folds over itself to form three germ layers
Germ layers
collection of cells formed during embryogenesis that will give rise to future body tissues
Diploblasts
animal that develops from two germ layers (most internal to external: endoderm, non-living layer, ectoderm)
Triploblasts
animal that develops from three germ layers (most internal to external: endoderm, mesoderm, ectoderm)
Blastomeres
The cells resulting from subdivision of the material of the egg where cells are not growing, only dividing
What are the 2 groups of Triplobastic animals based on development?
- Protostomes = “mouth first”
- Deuterostomes = “mouth second”
What is an example of some animals having larval forms that are different from adult?
Insect metamorphosis
Incomplete metamorphosis
larval forms are smaller, wingless version of adult
Complete metamorphosis
larval stage differs greatly in body plan compared to adults
Hox genes
Master control gene that can turn on or off large numbers of other genes during embryogenesis
- Important factor in determining body plan
Duplications across evolutionary time _______ correlate with body plan complexity.
positively
Bilateral symmetry
type of symmetry in which there is only one plane of symmetry, so the left and right halves of an animal are mirror images
Radial symmetry
division in any direction along oral/oboral axis results in two halves that are mirror images
Rotational symmetry
division in any direction along oral/oboral axis results in two identical halves, with one copy rotated 180o
Porifera-sister hypothesis
Systematic studies typically place Porifera (sponges) as sister to all other animals; first branch off the ToL
- “primitive” traits: lack germ layers, nerve and muscle cells
- cells that resemble choanoflagellates
What is the truth of the Porifera-sister hypothesis?
Recent studies using DNA sequence data place Ctenophora (comb jellies) as sister to all other animals
- traditionally grouped closer to Cnidaria (includes jellyfish)
- lack Hox genes
Still debated, but if true then either:
- porifera lost complexity (e.g. nerve & muscle cells)
- complexity evolved twice
What are key traits of Metazoa?
- muscle cells
- neurons
- diploblasty
Cambrian explosion
time during the Cambrian period when most of the animal phyla in existence today evolved
- Rapid diversification of animals, including new body plans
What are possible mechanisms of the Cambrian explosion?
- Increase in atmospheric oxygen
- Increase in oceanic calcium
- Changes in ecology and species interactions
- Expansion of Hox genes
