Umbrella octopus

Umbrella octopuses, members of the family Opisthoteuthidae, are pelagic octopuses whose name derives from Ancient Greek words meaning "back" and "squid." Their most distinctive feature is a web of skin connecting their arms, which, when spread, gives them the appearance of an opened umbrella. Unlike some other cirrate octopuses, they lack an intermediate web; instead, the web between their arms serves a similar function, and the absence of this intermediate structure creates indentations along the outer edges of the arms, reinforcing the umbrella-like shape. Their bodies are supported by a broad, U-shaped internal shell that anchors muscles for a pair of small fins on the mantle. These fins are far less developed than in other cirrate families and serve primarily as stabilizers when the animal swims using a medusoid motion of its arms and webbing. The oral surface is positioned below the mantle, with the web and arms surrounding the mantle’s bottom. Their outer skin is notably delicate, and when damaged, white spots appear on the surface.

In defense, umbrella octopuses mimic a ballooning behavior by extending the web between their arms as much as possible and curving the outer edges of the arms inward so that only the edges touch the ground. They extend their fins parallel to the floor for balance or curve them around the mantle, and have been observed holding this posture for up to five and a half minutes. Another defensive tactic is web-inversion, where the arms are turned upward and the oral surface faces outward, either toward the floor or with the octopus lying laterally. These behaviors may also occur during feeding, though this could be due to stress from captivity. When resting on the seafloor, they employ either bottom-resting—erecting the mantle and curving arm edges inward to contact the floor—or flat-spreading, where the arms and web are spread parallel to the bottom with the head angled slightly backward. These deep-sea creatures have been found in the Clipperton-Clarion Fracture Zone in the Pacific Ocean at depths around 4,800 meters, as well as in the South China Sea, typically hovering between 3,000 and 4,000 meters below sea level.