Opisthoteuthis calypso is a species of genus Opisthoteuthis, which are known as the cirrate octopuses. Octopuses in this genus are known as the flapjack octopuses and can be found in a variety of oceans across the world.
The species of this genus show distinctive characteristics among the class Cephalopoda, including an oval shaped body compressed along the longitudinal axis, a gelatinous consistence and a large interbrachial web.
This species generally has a mantle length of 5 cm. This web is what has given them their common name “flapjack” or “pancake devil fish”. Other distinctive features include the presence of two small fins on the mantle, an internal U-shaped shell that has a groove along its outer surface. This particular species has eight, subequal arms (of an uneven length). As adults, they tend to have 47–58 suckers on each of these eight arms. Their cirri (small tassel-like appendages on the surface of the octopus) are on the shorter end, with a length reaching up to 5 mm. This is what differs them from other members of the Opisthoteuthis genus. Due to the delicate consistency of the species, captured specimen are often in poor condition and therefore near impossible to identify other particular distinguishing features.
This species is typically found in the South Eastern Atlantic Ocean and Mediterranean Sea, although they are quite rare and therefore distribution is not well known. In terms of habitat, the species has been found on muddy bottoms at depths of 365 meters in the South East Atlantic and 2208 meters in the Mediterranean. Recent studies have found 11 specimens around the Balearic Islands in the western Mediterranean, and others 38 others have been found at depths ranging from 871 to 1420 meters in the Sardinian Channel of the central Western Mediterranean. This species was previously mistaken for O. agassizi, a species in the same genus. Since, previous captured specimen of O. agassizi, that were found in the Mediterranean have been accredited to O. calypso, and is now believed to be the sole Opisthoteuthis species in the area.