"Females of this unusual octopus species sequester themselves in thin, translucent shells with which they drift across the open seas. Paper nautiluses, also called argonauts, secrete the shells to serve as cases for their eggs—but it has recently been discovered that they also function as air-trapping ballast tanks, which allow the cephalopods to hang effortlessly in the water column without sinking. Clever octopodes!"
The blue-ringed octopuses (genus Hapalochlaena) are three (or perhaps four) octopus species that live in tide pools and coral reefs in the Pacific and Indian Oceans, from Japan to Australia (mainly around southern New South Wales and South Australia, and northern Western Australia). This octopus is one of the most venomous animals on the planet. https://www.facebook.com/somersault1824
Megaleledone setebos, a shallow-water circum-Antarctic species from the Southern Ocean. It is the closest living relative to deep-sea octopuses. The specimen shown is a juvenile; adults reach a total length of nearly 1m.