This is an Blanket Octopus.
Photos by Steve Hamedl Feb 2011 Molasses Reef.
Location was Key Largo, FL Tremoctopus violaceus VIDEO of Photos
Size: This female was about 3 feet long; Males are miniscule;
Audubon Field Guide;
Reef Fish ID 3rd ed; pg
Tremoctopus is a genus of pelagic cephalopods,
containing four species that occupy surface to mid-waters in
subtropical and tropical oceans. They are commonly known as blanket
octopuses, in reference to the long transparent webs that connect the
dorsal and dorsolateral arms of the adult females. The other arms are
much shorter and lack webbing.
These species exhibit an extreme degree of
sexual dimorphism. Females may grow to over 2 metres in length whereas
the tiny males are at most a few centimeters long. The males have a
specially modified third right arm which stores sperm, known as a
hectocotylus. During mating, this arm detaches itself and crawls into
the mantle of the female to fertilize her eggs. The male dies shortly
after mating. The females carry over 100,000 tiny eggs that are
attached to a sausage-shaped calcareous secretion held at the base of
the dorsal arms and carried by the female until hatching.
These species have evolved an unusual defense mechanism: blanket
octopuses are immune to the poisonous Portuguese man o' war, whose
tentacles the male and immature females rip off and use for defensive
purposes. Also, unlike many other octopuses, the blanket octopus does
not use ink to intimidate potential predators. When threatened, the
female unfurls her large net-like membranes that spread out and billow
in the water, greatly increasing her apparent size. More about Blanket Octopus: http://tolweb.org/Tremoctopus