Medusa

Definition

Medusa is a life stage in the life cycle of certain cnidarians, characterized by a free-swimming, umbrella-shaped body with tentacles hanging down. This stage is primarily associated with jellyfish, where the medusa form is responsible for sexual reproduction and dispersal. Medusae are equipped with specialized cells called cnidocytes that contain nematocysts, allowing them to capture prey and defend against predators.

5 Must Know Facts For Your Next Test

1. Medusae are primarily responsible for the sexual reproduction of jellyfish, releasing sperm and eggs into the water for external fertilization.
2. The medusa stage can vary significantly in size and morphology among different species of jellyfish, from small to large forms.
3. Medusae have a simple nervous system that allows them to respond to environmental stimuli, enabling them to swim effectively in the water.
4. In some species, such as the moon jellyfish (Aurelia aurita), the medusa can live for several months, while others have shorter lifespans.
5. The transition from the polyp to the medusa stage can occur through a process called strobilation, where the polyp divides transversely to produce multiple medusae.

Review Questions

• How does the medusa stage differ from the polyp stage in cnidarians, particularly in terms of structure and function?
  • The medusa stage differs from the polyp stage primarily in its morphology and lifestyle. Medusae are free-swimming and have an umbrella-shaped body with tentacles, while polyps are sessile and have a tubular shape. Functionally, medusae are adapted for sexual reproduction and dispersal through the water column, whereas polyps typically reproduce asexually and serve as the attachment phase in the life cycle.
• Discuss the ecological role of medusae within marine ecosystems and their interactions with other marine organisms.
  • Medusae play a crucial ecological role in marine ecosystems as both predators and prey. They feed on small fish, plankton, and other marine organisms using their stinging tentacles to capture prey. In turn, they are also a food source for larger marine animals such as sea turtles and some fish species. The presence of medusae can influence local food webs and even impact fish populations due to their predation on larval stages of various species.
• Evaluate how changes in oceanic conditions might affect the population dynamics of medusae and their life cycle processes.
  • Changes in oceanic conditions such as temperature rise, ocean acidification, and nutrient availability can significantly impact the population dynamics of medusae. Warmer waters may favor the growth of jellyfish populations by promoting higher reproductive rates during their medusa stage. Additionally, increased nutrient runoff can lead to algal blooms that provide abundant food for young medusae. However, these changes could also disrupt existing marine ecosystems by affecting predator-prey relationships and potentially leading to jellyfish blooms that outcompete other species for resources.

Related terms

polyp: A sessile life stage in cnidarians characterized by a cylindrical body and tentacles, typically attached to a substrate.

cnidocytes: Specialized cells in cnidarians that contain stinging structures called nematocysts, used for capturing prey and defense.

jellyfish: A common name for medusae of certain cnidarian species, known for their gelatinous bodies and ability to float or swim in the water.