Key Terms
Exception
In bees, wasps, ants, males develop from unfertilized eggs and are haploid. This is haplodiploidy.
Sexual
Sperm fertilizes egg; produces a diploid zygote. Default for most animals.
Parthenogenesis
Offspring develop from a gamete without fertilization. Only females produce these offspring (eggs have nutrients; sperm
Diploblasts
2 germ layers (ectoderm + endoderm). Typical of radially symmetrical animals (Cnidaria).
Triploblasts
3 germ layers. Typical of bilaterally symmetrical animals.
Incomplete metamorphosis (grasshoppers)
Young resemble wingless adults; wings develop gradually through molts.
Nusslein-Volhard and Wieschaus
Did the foundational Hox gene work using fruit fly mutations. Their experiments identified which genes control which bod
Coelom advantages
Cushions organs; allows organs to grow and move; aids motility; enables gas and nutrient diffusion.
Anomalocaris
Dominant arthropod-like predator; over 1 meter; compound eyes; likely apex predator of the Cambrian.
Trilobites
Dominant Cambrian arthropod; among the first animals with vision; went extinct in the Permian mass extinction.
Acoelomate
Triploblast with no body cavity; mesoderm fills the space.
Archenteron
Primitive gut formed during gastrulation. Bilateral symmetry: one plane of symmetry; produces left/right mirror image.
Blastomere
Cell produced by cleavage of the zygote. Blastopore: opening from the primitive gut to the outside of the embryo.
Body plan
The fixed morphology established during embryonic development. Cambrian explosion: 542-488 MYA; rapid appearance of most
Cleavage
Mitotic divisions of the zygote; no net cell growth. Coelom: fluid-filled body cavity lined by mesoderm.