What are the general characteristics of jellyfish?

1. Body Structure: Jellyfish have a gelatinous, umbrella-shaped, radially symmetrical body with a flexible bell-like structure. They lack a backbone, hence they are invertebrates.

2. Mesoglea: The body is composed of a jelly-like substance called mesoglea, which is sandwiched between two layers of thin tissues (ectoderm and endoderm).

3. Absence of Brain: Jellyfish do not have a centralized brain or nervous system. Instead, they have a decentralized nerve net.

4. Radial Symmetry: Jellyfish exhibit radial symmetry, meaning that their body parts are arranged in a circular pattern around a central axis.

5. Tentacles: Jellyfish have tentacles, which are long, trailing appendages that extend from the bell. Tentacles are used for capturing prey, defense, and sensory purposes.

6. Stinging Cells: Many jellyfish species have stinging cells called nematocysts. Nematocysts contain stinging threads that can inject venom when triggered by contact.

7. Bioluminescence: Jellyfish often exhibit bioluminescence, the ability to produce and emit light through chemical reactions. This phenomenon helps them attract prey and communicate with each other.

8. Plankton and Nekton: Some jellyfish species are planktonic, meaning they drift with ocean currents, while others are nektonic, capable of propelling themselves through the water.

9. Reproduction: Jellyfish have complex life cycles involving both asexual (budding) and sexual (gamete release and fertilization) reproduction.

10. Lifespan: Jellyfish can have varying lifespans depending on the species. Some species may live for only a few weeks, while others can survive for several years.

11. Habitat: Jellyfish are found in all oceans, from coastal waters to the deep sea. They can be found in warm tropical waters as well as cold polar regions.

12. Ecological Importance: Jellyfish are predators and prey for other marine organisms, thus contributing to the balance of the ecosystem. They also serve as a food source for humans in certain cultures.

Jellyfish are fascinating marine creatures that showcase unique characteristics and adaptations that have allowed them to thrive in various aquatic environments for millions of years. Their diverse forms, bioluminescent displays, and ecological impacts make them an important part of understanding marine ecosystems.