Jellyfish: Ancient Creatures of the Sea"

Jellyfish are marine animals that belong to the phylum Cnidaria and the class Scyphozoa, though some also belong to Cubozoa and Hydrozoa. They have soft, gelatinous bodies and are known for their umbrella-shaped bells and trailing tentacles, which contain specialized stinging cells called nematocysts. These cells help them capture prey and defend against predators.

Jellyfish have a simple body structure with no brain, heart, or bones. Instead, they rely on a nerve net to sense their environment and move using rhythmic pulsations of their bell. They are found in oceans worldwide, from surface waters to the deep sea, and can vary greatly in size, from a few millimeters to over two meters in diameter.

Some jellyfish species, such as the box jellyfish, have venom that can be dangerous to humans, while others are harmless. They play an essential role in the marine ecosystem as both predators and prey, feeding on plankton, small fish, and other jellyfish. Certain species, like Turritopsis dohrnii, are even known for their ability to revert to an earlier life stage, making them biologically immortal.