Animal Development and Body Plans

Metamorphosis vs. Growth and Development
- Some animals undergo metamorphosis, while others experience growth and development.
- Metamorphosis involves distinct changes in body form and can be more drastic, as seen in insects.
- Growth and Development: Less drastic changes involving physiological processes primarily driven by hormonal signals.
  - Example: Humans do not undergo metamorphosis but go through growth and development.

Examination of body plans and morphology in animals, highlighting fundamental traits such as symmetry.

Radial Symmetry
- Organisms can be divided into similar halves by multiple planes (like cutting a pizza).
- Prominent in sessile (anchored) and planktonic (drifting) organisms.
- Benefits include equal responsiveness to stimuli from all directions, advantageous for feeding and predator evasion.
Bilateral Symmetry
- Divided into left and right halves, which are mirror images.
  - This symmetry facilitates more directed movement and is found in more active animals.
- Bilateral organisms typically possess
  - Specialized sensory organs.
  - More developed central nervous systems.
- Anatomical orientation:
  - Head-tail axis (anterior-posterior): Anterior = toward the head; Posterior = toward the rear.
  - Dorsal-ventral axis: Dorsal = back; Ventral = belly side.

Example of slicing a lobster or owl to demonstrate symmetry:
- Anterior to posterior cut results in mirrored halves, while superior-inferior cuts do not.

Development of multicellular organisms influenced by environmental pressures.
- Eukaryotes arose before early multicellular animals, which exhibit varying complexities.
- Origin of Multicellular Animals:
- Emerged from ancestral cells, like choanoflagellates, which resemble sponge collar cells.
- Demonstrates the evolutionary path from single-celled to multicellular organisms.

Neoproterozoic Era (1 billion - 541 million years ago):
- Fossil evidence suggests emergence of small multicellular animals predating the Cambrian Explosion, including early mollusks and sponges.
- Evidence of early predation illustrated in fossils like Cloudina, which were drilled into by predators.
- Rise in atmospheric oxygen contributed to diversification and evolutionary pressures.

Hox genes played a role in developmental variation, allowing morphological diversity.
The Paleozoic Era saw the emergence of many phyla and significant diversification.
Land colonization by animals occurred around 363 million years ago, leading to amphibians and amniotes.

Notable for the presence of first corals and the diversification of marine species, including jellyfish.
Transition of species between land and aquatic environments observed (e.g., whales).
Dinosaurs dominated before their mass extinction facilitated mammalian diversification.

Animal genomics provide insights into evolutionary relationships, with sponges as a reference group (outgroup).

Metazoa includes all animals whereas Eumetazoa includes those with true tissues.
Phyla categorized by body symmetry, with most being bilaterally symmetric.

Radially symmetric animals with diploblastic tissues: two layers of cells (ectoderm and endoderm).
Body forms:
- Polyp: Sessile, like hydras, with tentacles for feeding.
- Medusa: Free-floating, like jellyfish.
Cnidocytes: Specialized stinging cells used for capturing prey.
- Example: Box jellyfish with potent venom.
Coral reefs formed by colonial organisms that secrete calcium carbonate, providing biodiversity hot spots.

Coral reefs and mollusks specifically threatened by environmental changes, pollution, habitat destruction, and overharvesting.
Over 10% of North American freshwater pearl species have gone extinct due to these pressures.

Dissections planned for Tuesday, covering:
- Clams
- Earthworms
- Grasshoppers
- Starfish
Best practices for dissection, including handling tools and maintaining hygiene, will be reviewed in lab.