Box jellyfish
Although the notoriously dangerous species of box jellyfish are largely restricted to the tropical Indo-Pacific region, various species of box jellyfish can be found widely in tropical and subtropical oceans, including the Atlantic Ocean and the east Pacific Ocean, with species as far north as California ("Carybdea confusa"), the Mediterranean Sea ("Carybdea marsupialis") and Japan (such as "Chironex yamaguchii"), and as far south as South Africa (for example, "Carybdea branchi") and New Zealand (such as "Copula sivickisi").
Apolemia uvaria
String jellyfish are colonial animals that may reach 3 m in total length and have a diameter of 2–5 cm. The colony is formed of a central string, bearing groups of pink and white tentacles, which clump together or extend. The whole colony has a gas float at the front and a set of swimming bells. This colonial animal is pelagic and is found in oceans worldwide in midwater. These ocean predators act like drift nets, spreading their tentacles to catch plankton. The tentacles give a painful sting and are best avoided.