Some species have venom that can be dangerous to humans. For instance, the box jellyfish is among the most venomous animals in the world. However, most jellyfish are harmless and may only cause mild skin irritation.
Jellyfish usually feed on plankton, small fish, and other tiny sea creatures. They capture prey and bring it into their mouth opening, which also serves as an anus — a single opening for both ingestion and waste expulsion.
