Animls - Phylum Cnidaria

PHYLUM CNIDARIA =

• Includes sea jellies, anemones, corals, sea pons

• Body plan alternates between polyp and medusa forms (polymorphism).

• Possess nematocysts (stinging cells) for defense and capturing prey, containing paralyzing neurotoxins.

• Radial symmetry.

• Mostly marine habitat, some freshwater species.

• Carnivorous predators; use tentacles with nematocysts to capture prey and pull it into their mouth

FEEDING

• Prey is pushed into the gastrovascular cavity for extracellular digestion via enzymes.

• Undigested material is expelled through the mouth (also functions as anus).

RESPIRATION, INTERNAL TRANSPORT & EXCRETION

• Respiration occurs via diffusion due to the thin body (two cell layers).

• Material passes through the body via diffusion.

• Wastes are excreted by diffusion.

RESPONSE

• Gather information using specialized sensory cells but lack cephalization (discrete head).

• Organized around a nerve net around the mouth.

• Sensory cells include: Chemoreceptors (chemical), Thigmoreceptors (touch), Photoreceptors (light), Statocysts (balance).

LOCOMOTION

• Medusa stage is motile (free-swimming), polyp stage is sessile.

• Exceptions: Hydra tumbles, sea anemone detaches from substrate.

• Most animals move their bodies using a hydrostatic skeleton.

REPRODUCTION

• Asexual: budding from polyps or medusa

• Sexual:

  • Medusa release sperm and egg

  • Monoecious or dioecious

  • Free swimming larvae

SYMBIOSIS

• Predators and prey

• Neurotoxins

• Corals (foundation for ecosystem)