Body Plans, Embryonic Development, and Cnidarians

How is animal classification determined?

Symmetry, tissues, body cavities, developmental patterns, and segmentation

What is radial symmetry?

Divided in two equal halves by any plane passing through the center

What group of animals exhibit radial symmetry?

Cnidarians

What is bilateral symmetry?

Divided in two equal halves by only one plane passing through the center

Why do most animals exhibit bilateral symmetry?

Directional movement: move in a consistent direction. Cephalization: concentration of nerve cells and sensory structures at anterior end.

What germ layers (embryonic tissue layers) are present in diploblastic organisms?

Ectoderm and endoderm

What layers are in triploblastic organisms?

Ectoderm, mesoderm, and endoderm

What is an acoelomate?

No body cavity (besides gut)

What is a pseudocoelomate?

Body cavity between the mesoderm and endoderm (pseudocoelom)

What is a coelomate?

Body cavity within the mesoderm (coelom)

What does the blastopore become in protostomes?

Mouth first, anus next if present

What does the blastopore become in deuterostomes?

Anus first, mouth next

What is segmentation?

Body is made of linearly arranged, similar units.

What advantages does segmentation provide?

Segments may contain redundant organ structures (can survive on their own), segments can move independently, allowing for more efficient and flexible movement

What are the major steps of embryonic development?

Fertilization, cleavage, blastula, gastrulation, gastrula

What is fertlization?

Sperm penetrates egg membrane, egg activates, nuclei fuse

What is cleavage?

Rapid division of zygote into smaller cells (blastomeres)

Does the overall size of an embryo change during the initial stages of development?

NO

What are cleavage patterns dependent on?

Amount of yolk

What is a blastula?

Mass of cells around fluid-filled cavity (blastocoel)

What is gastrulation?

Series of cell shape changes and cell movements

What happens during gastrulation, specifically?

One side of blastula moves inward to create gastrula; indentation = archenteron

What is the opening to the archenteron called?

Blastopore

What organisms make up Phylum Cnidaria?

Jellies, corals, anemones

How many layers of tissue do Cnidarians have?

Two - diploblastic

What types of symmetry do Cnidarians exhibit?

Radial symmetry.

Do Cnidarians have tissues?

True tissues, but no organs

What type of feeding do Cnidarians exhibit?

Carnivores

How do Cnidarians capture prey?

With cnidocytes (nematocysts are harpoons with toxins).

How do Cnidarians detect signals?

Have sensory cells to detect light, gravity, and touch.

Describe the polyp body plan.

Cylindrical, usually attached

Describe the medusa body plan.

Umbrella-shaped, freely-moving

What are polyp vs. medusa body plans used for cnidarian life cycle?

Polyp: mostly asexual reproduction to form medusa. Medusa: mostly sexual reproduction to produce gametes and zygotes

What is a nematocyst?

Lie within the cnidocyte. Harpoon-like, used to capture prey. Some have venom, others just stick to prey.

What are the five cnidarian classes?

Anothozoa, cubozoa, hydrozoa, scyphozoa, staurozoa

What organisms are in the class Anothozoa?

Sea anemones, most corals, sea fans

What are characteristics of Anothozoa?

Solitary and colonial polyps

With what organisms do Anothozoa have smybioses with?

Dinoflagellates: photosynthesize, providing nutrients to coral

What organisms are in the class Cubozoa?

Box jellies

What are the characteristics of Cubozoa?

Strong swimmers, voracious predators

What organisms are in class Hydrozoa?

Hydroids (Hydra, Portuguese man of war)

What are the characteristics of Hydrozoa?

Often colonial, polyp and medusa

What organisms are in class Scyphozoa?

True jellies

What are the characteristics of Scyphozoa?

Dominant medusa stage, swim with jet propulsion

What organisms are in class Staurozoa?

Star jellies

What are characteristics of Staurozoa?

Stalked medusa, few species