Union between egg and sperm
Fertilization does what 2 things?
- Recombination of genes and restores diploid status
- Also causes the start of cleavage
What is a small ball of cells called (egg)?
Patterns of cleavage depends on?
- Quantity and type of yold present
- Type of symmetry inherited
- Very little yolk
- Evenly distributed in egg
- Cells are surrounded by a membrane.
- The cleavage furrow extends through the egg
- Yolk is densly concentrated at the vegetal pole
- Disc shaped mass on top of yolk mass=vegetal pole
- Pie-like characteristic of animals with backbones
Cells of a blastomere are no identified as a specialty cell. If one cell is separated, it will form its own new blastomere.
Symmetry of echinoderms and chordates
Cleavage planes are oblique to the polar axis (animal/vegetal poles)
- Cluster of cells as a result of cleavage
- Outer layer becomes ectoderm
- Forms germ layers
- New cell association occurs to body plan (specialized)
- Invagination occurs-Deurterostomes, protostomes
Epithelium of body and nervous system
Muscles, reproductive, peritoneum
Epithelial lining of digestive tract
Echinodermata includes and means?
- External spines
- Starfish, sea cucumbers, sea lilies, sand dollars
Charcteristic of echinoderms
- Spiny endoskeleton
- Water-vascular system
- Pericerllariae-Small pincers on the spine to remove debris
- Dermal branchiae or papulae
- Bilateral and pentaradial symmetry
What is bilateral?
- Marine bottom dwellers
- Not found in fresh or brakish waters