Cirrothauma is a genus of deep water octopuses from the cirrate family Cirroteuthidae. Opisthoteuthis calypso is a species of genus "Opisthoteuthis", which are known as the cirrate octopuses. Cuttlefish, squid, spirula, vampire squid, and cirrate octopuses have small internal shells. Luteuthis is a small genus of cirrate octopuses from the family Opisthoteuthidae. Cirrate octopuses lack the ink sac. This form has been interpreted as a cirrate octopus. Cirroteuthidae is a family of cirrate octopuses comprising three species in two genera. Cirroteuthis muelleri is one of the largest cirrate octopuses, growing to a length of . Opisthoteuthidae fall into the cirrate octopod group, meaning they have fins. Cirrate octopuses are noteworthy for lacking ink sacs. In cirrate octopods suckers and cirri run and alternate on the entire length. The cirrate octopuses are deep sea species that have been relatively little studied. Cirrate octopuses cannot produce jet propulsion and rely on their fins for swimming. The cirrate species are often free-swimming and live in deep-water habitats. Cirrate octopuses possess a well-developed internal shell that supports their muscular swimming fins.