Medusa

Definition

Medusa refers to a free-swimming, umbrella-shaped life stage of certain cnidarians, such as jellyfish. This form is characterized by its gelatinous body and tentacles that hang downwards, allowing it to float in water and capture prey with specialized stinging cells called cnidocytes. The medusa stage contrasts with the polyp stage, showcasing the complex life cycle of these organisms.

5 Must Know Facts For Your Next Test

1. Medusas are primarily found in marine environments, although some species can inhabit freshwater ecosystems.
2. They can reproduce both sexually and asexually, often depending on their life cycle stage and environmental conditions.
3. Medusas have a unique structure called the bell, which contracts to propel them through the water, allowing for movement and feeding.
4. Many species of medusas exhibit bioluminescence, producing light to attract prey or deter predators.
5. The size of medusas can vary greatly; some are only a few centimeters across, while others can exceed two meters in diameter.

Review Questions

• How does the structure of the medusa contribute to its lifestyle and feeding habits?
  • The medusa's umbrella-shaped structure allows it to move efficiently through water by contracting its bell, propelling itself forward. This unique design helps in capturing prey as its tentacles, lined with cnidocytes, trail beneath it. When a potential meal comes into contact with the tentacles, the stinging cells can immobilize the prey, allowing the medusa to consume it more easily.
• Compare and contrast the medusa stage with the polyp stage in cnidarians regarding their functions and reproductive strategies.
  • The medusa stage is free-swimming and primarily focused on reproduction, often engaging in sexual reproduction by releasing gametes into the water. In contrast, the polyp stage is typically sessile and can reproduce asexually through budding. While both stages play essential roles in the life cycle of cnidarians, they exhibit distinct adaptations for their environments: medusas for mobility and reproduction in open waters, and polyps for stability and growth on substrates.
• Evaluate the ecological roles of medusas in marine ecosystems and their impact on food webs.
  • Medusas play significant ecological roles in marine ecosystems as both predators and prey. As consumers, they help control populations of smaller planktonic organisms, contributing to energy transfer within the food web. Additionally, they serve as a food source for larger predators like sea turtles and some fish species. However, changes in their populations can have cascading effects on marine ecosystems; for example, an overabundance of medusas may indicate imbalances in marine environments or lead to declines in fish populations due to competition for resources.

Related terms

polyp: The sessile, cylindrical form of cnidarians that attaches to a substrate and typically reproduces asexually.

cnidocyte:

Specialized stinging cells found in cnidarians, used for defense and capturing prey.

planula: The free-swimming larval stage of cnidarians that develops from fertilized eggs before transforming into polyps.