Medusa

Definition

Medusa refers to a life stage of certain cnidarians, characterized by a free-swimming, umbrella-shaped body and tentacles that hang down. This stage is crucial for reproduction, as medusae often release eggs and sperm into the water, leading to the formation of new polyps. Medusae are typically associated with jellyfish, but they also appear in other cnidarian groups, highlighting their significance in the life cycles of these organisms.

5 Must Know Facts For Your Next Test

1. Medusae are often bell-shaped and can vary greatly in size, from just a few millimeters to several meters across.
2. During the medusa stage, many cnidarians can reproduce sexually, releasing gametes into the surrounding water for external fertilization.
3. Some species of medusae possess bioluminescent properties, allowing them to produce light in dark ocean environments.
4. Medusae are part of the life cycle of jellyfish, which alternates between polyp and medusa stages, showcasing their complex reproductive strategies.
5. The movement of medusae is primarily achieved through pulsations of their bell, allowing them to swim or drift with ocean currents.

Review Questions

• How does the medusa stage differ from the polyp stage in cnidarians, and what role does each play in the organism's life cycle?
  • The medusa stage is free-swimming and bell-shaped, while the polyp stage is sessile and tubular. Medusae primarily function in sexual reproduction by releasing eggs and sperm into the water, whereas polyps often reproduce asexually by budding. This alternating life cycle allows cnidarians to adapt to different environmental conditions and maximize reproductive success.
• Discuss the ecological significance of medusae within marine ecosystems, including their role as both predators and prey.
  • Medusae play a vital role in marine ecosystems as both predators and prey. As predators, they consume various planktonic organisms, contributing to controlling populations within the food web. Conversely, medusae serve as important food sources for larger marine animals like sea turtles and certain fish species. Their presence can influence local biodiversity and nutrient cycling within marine habitats.
• Evaluate the impact of environmental changes on medusa populations and how this may affect broader marine ecosystems.
  • Environmental changes such as rising ocean temperatures, pollution, and habitat degradation can significantly impact medusa populations by altering their reproductive rates and survival. An increase in nutrient runoff may lead to harmful algal blooms, which can create hypoxic conditions that favor jellyfish over traditional fish species. This shift can disrupt food webs and biodiversity, illustrating how medusae can serve as indicators of environmental health while highlighting their potential to dominate altered ecosystems.

Related terms

polyp: A sessile life stage in cnidarians, typically cylindrical in shape with a mouth at one end surrounded by tentacles.

cnidocyte: Specialized cells found in cnidarians that contain stinging organelles called nematocysts, used for defense and capturing prey.

plankton: Tiny organisms that drift in water currents; medusae are considered planktonic during their free-swimming phase.