Jellyfish

Definition

Jellyfish are gelatinous, free-swimming marine animals that belong to the phylum Cnidaria. They are characterized by their umbrella-shaped bell and trailing tentacles that contain specialized cells called cnidocytes, which they use for defense and capturing prey. As part of the Cnidarian group, jellyfish share common features with other members like corals and sea anemones, highlighting their evolutionary significance in the marine ecosystem.

5 Must Know Facts For Your Next Test

1. Jellyfish have existed for over 500 million years, making them one of the oldest living creatures on Earth.
2. They are composed of about 95% water, giving them their characteristic jelly-like appearance.
3. Jellyfish can reproduce both sexually and asexually, often going through complex life cycles that include both polyp and medusa stages.
4. Some species of jellyfish are bioluminescent, producing light through chemical reactions within their bodies as a means of communication or predation.
5. Certain jellyfish, like the box jellyfish, possess potent venom that can cause serious injury or even death to humans.

Review Questions

• How do jellyfish use cnidocytes for survival and feeding?
  • Jellyfish utilize cnidocytes to capture prey and defend themselves from predators. These specialized cells contain nematocysts, which are tiny harpoon-like structures that can inject venom into their targets. When a jellyfish comes into contact with potential prey, its tentacles release these nematocysts, paralyzing or killing the prey before it is brought to the mouth for digestion. This ability to effectively capture prey is crucial for their survival in marine environments.
• Discuss the importance of the jellyfish life cycle in understanding their reproduction and ecological role.
  • The jellyfish life cycle includes several stages: the polyp stage, where they are attached to a surface, and the medusa stage, which is the free-swimming form. Understanding this cycle is important because it illustrates how jellyfish can reproduce both sexually and asexually. During favorable conditions, polyps can bud off new medusae or release sperm and eggs into the water for fertilization. This flexibility in reproduction allows jellyfish populations to thrive in varying environmental conditions, impacting marine food webs and ecosystem dynamics.
• Evaluate the ecological impact of jellyfish blooms on marine ecosystems and human activities.
  • Jellyfish blooms can significantly disrupt marine ecosystems and human activities. These blooms often result from overfishing, pollution, and climate change, leading to an increase in nutrient availability. The proliferation of jellyfish can outcompete fish larvae for food resources, affecting fish populations and ultimately impacting fisheries. Additionally, large blooms can clog fishing nets, damage boats, and even cause power plant shutdowns by obstructing cooling intakes. Therefore, understanding jellyfish blooms is crucial for managing marine ecosystems and mitigating their effects on human economic activities.

Related terms

Cnidocytes: Specialized cells found in Cnidarians, including jellyfish, that contain stinging organelles called nematocysts used for capturing prey and defense.

Medusa: The adult form of certain Cnidarians, including jellyfish, characterized by a bell-shaped body and tentacles hanging down.

Planula: The free-swimming larval stage of jellyfish that eventually settles and develops into a polyp before transforming into the medusa form.