Jellyfish

1. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, while some tend to be immobile anchored to the seabed by stalks.
2. The tentacles are armed with stinging cells and used to capture prey and defend against predators.
3. They are found all over the world, from surface waters to the deep sea, from marine to freshwater, but common in coastal zones worldwide.
4. Jellyfish are the oldest multi-organ animal group as they have been in existence for at least 500 million years.
5. Some of the species have a green fluorescent protein to cause bioluminescence.
6. A group of jellyfish is called a "smack" or a "smuck".
7. Jellyfish do not have brain or heart.

   

8. Other organisms without a brain include:

1. Sea star
2. Sea cucumber
3. Sea lily
4. Sea urchin
5. sea sponges
6. sea anemone
7. sea squirt