Lecture 8 Recording-2025-01-31T14:51:02.536Z

Overview of Jellyfish Life Cycle

• Focus on understanding the life stages of jellyfish (Scyphozoans)

  • Two main stages:

    • Medusa: Dominant stage in the life cycle, represents adult jellyfish; appears larger in diagrams.

    • Polyp: Smaller stage, described as somewhat boring in terms of activity.

Sexual Reproduction in Jellyfish

• Jellyfish display separate sexes:

  • Male Jellyfish: Produces sperm.

  • Female Jellyfish: Produces eggs.

• Fertilization involves the union of sperm and egg, leading to the development of a new organism.

• Developmental feature called strobilation:

  • This process results in the formation of structures that look like stacked saucers, leading to the development of new jellyfish.

Nervous System of Scyphozoans

• Introduction to the nervous system of jellyfish:

  • Decentralized system with nerve nets instead of a centralized brain.

  • The intensity of response to stimuli is determined by the frequency of stimulation, not by its intensity:

    • Example: Poking results in varying responses based on how often the stimulus occurs.

• Neuronal Structure:

  • Contains slow neurons that are gap junction-coupled, allowing for rapid signaling between nerve cells.

Sensory Structures

• Identifying sensory structures in jellyfish:

  • Statocyst: Detects orientation and gravity; consists of small granules that respond to gravitational forces.

  • Ocelli: Basic light-detecting structures that can sense the presence and intensity of light, but do not form images.

    • Help jellyfish navigate and avoid predators.

Ecological Adaptations

• Discussing ecological adaptations:

  • Transparency lets jellyfish evade visual predators; they are often hard to see in water.

  • Engage in diel vertical migration:

    • Predictable movement pattern, rising during the night to feed and descending during the day to avoid predation; phenomena coincide with changes in light conditions.

• The importance of metabolic waste management through specialized canals in their body for expelling waste.

Reproductive Isolation and Confusion

• Clarifying confusion regarding the reproductive structures:

  • Gametes forming at the base, often leading to misconceptions about their function.

  • Gastric pouches: Function to process food and host gametes.

  • Some previously held assumptions about the presence of polyp stages in certain jellyfish are now deemed false; certain structures are essentially modified medusae attached to the ocean floor.

  • Miscommunication regarding developmental processes has been highlighted and corrected.