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Most species have large, muscular females, ca. 1 m or more in total length, that occupy surface waters of tropical and subtropical oceans. In females the dorsal and dorsolateral arms are distinctly longer than arms III and IV and are connected by an extensive web which is absent from the other arms.
Figure. T. violaceus swimming just above the shallow ocean floor. Note the string-like structure trailing from the broad web of arm I. This "string" is actually the slender arm I extending beyond the web. Posterolateral view of T. violaceus swimming just above the shallow ocean floor. Photographed by Rob Rush at 68 feet deep off Delray Beach Ledge, Florida, USA (near 26°N 80°W), May 12, 2001, 9:06 AM local time.
Large ocelli can be displayed on the dorsal web. This web and the slender tip of the arms can, apparently, be autotomized along visible "fracture" lines. The autotomized arms and membranes presumably wiggle to distract or cling to a predator while the octopod swims away. Evidence for this and additional photographs of free-swimming T. violaceus can be seen here. Apparently the web is only extended when the octopod is threatened. A video on YouTube shows the large web rolled up and held close to the mouth. The blanket octopod seen in this video was filmed in the Sea of Japan (T. Kubodera, pers. comm.)
Figure. Same individual of T. violaceus pictured above, showing web and ocelli on arm I. Photographed by Rob Rush.
The color phase most typically associated with T. violaceus is with silvery sides and a very dark purple/blue dorsal surface.
Figure. The picture of T. violaceus on the left, taken in an aquarium, shows the typical color pattern. Photograph taken by Vicente Hernandez. The photograph on the right of Tremoctopus sp. taken from a submersible shows the octopod swimming at a depth of 340 m and about 5 m above the bottom in Hawaiian waters. An AVI format video clip of this individual is available at Cephalopods in Action. Submersible photograph courtesy of the Hawaii Undersea Research Laboratory.
An argonautoid ...
- with extensive web between dorsal four arms; web virtually absent between other arms (females).