Chiropsalmus quadrumanus
Chiropsalmus quadrumanus, commonly known as the four-handed box jellyfish, is a species of box jellyfish found in the western Atlantic Ocean, the Gulf of Mexico and the Pacific Ocean. The sting is venomous and dangerous to humans, especially children.
Phacellophora camtschatica
This cool-water species can be found in many parts of the world's oceans. It feeds mostly on smaller jellyfish and other gelatinous zooplankton, which become ensnared in the tentacles. Because the sting of this jellyfish is so weak, many small crustaceans, including larval crabs ("Cancer gracilis") and Amphipoda, regularly ride on its bell and even steal food from its oral arms and tentacles. The lifecycle of this jellyfish is well known, because it is kept in culture at the Monterey Bay Aquarium. It alternates between a benthic stage attached to rocks and piers that reproduces asexually and the planktonic stage that reproduces sexually in the water column; both males and females occur in the plankton.