Smallest octopus family

No less than three separate taxonomic families of octopus each contain just a single species. These are: Vitreledonellidae, containing the glass octopus Vitreledonella richardi; Alloposidae, containing the seven-arm octopus Haliphron atlanticus; and Ocythoidae, containing the football octopus Ocythoe tuberculata. A fourth family, Amphitretidae, contains two very similar species, known as telescope octopuses, which some octopus researchers consider to be merely two subspecies of the same single species.

The glass octopus and the telescope octopus(es) species are very distinctive because they are transparent, gelatinous and almost colourless, so that unless viewed at close range they are all but invisible. Yet they are not minute, the glass octopus measuring up to 45 cm long in total length. Another transparent, jelly-like species is the much smaller, well-named gelatinous octopus Bolitaena pygmaea, which attains a maximum total length of only 8.5 cm.