Please note that the content of this book mainly consists of articles that are available online from Wikipedia or other free sources. The group of octopuses (Octopodiformes or Vampyropoda) includes true octopuses (Octopoda), cirrate octopuses (Cirroctopoda), and vampire squid-like creatures (Vampyromorpha). They are characterized by having eight arms. The vampire squid-like creatures possess an additional pair of retractable filaments between the first two pairs of arms (counted from the head), which are used as sensory organs. The early development of octopuses in the egg and the intermediate position of the vampire squid-like creatures provide evidence that the group descends from originally ten-armed cephalopods.