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Blanket Octopus

Tremoctopus violaceus

If you’re seeking out size differences, look no farther than the Blanket Octopus. The females can be more than 50 times bigger than the males. It’s one of the most extreme examples of sexual dimorphism in the animal kingdom!

This species is named for the “blanket” found on adult females — that’s the webbing between arms. When threatened, the octopus flares out her webbing so she looks even bigger!

Size

Females: 39 in long (1 m) Males: 1 in long (2.4 cm)

Lifespan

3-5 years (females)
1-2 years (males)

Habitat

Shallow seas — open water

Diet

Small mollusks and fishes

Range

Tropical and subtropical oceans around the world

Predators

Unknown

superpower

Stinging Weapons

Adult females rely on their blanket for protection, but males and young females carry weapons — Portuguese man-o’-war tentacles!

deep dive

SCIENTIFIC NAME: Tremoctopus Violaceus

NICKNAMES: Common Blanket Octopus or Violet Blanket Octopus

This genus consists of four blanket octopus species: Tremoctopus gelatus, Tremoctopus robsoni, Tremoctopus gracilis, and Tremoctopus violaceus.

Blanket Octopuses belong to the same superfamily as Paper Nautiluses (Argonauts), Argonautoidea. This family is named after the Greek mythology because of their habitat of drifting in the ocean currents, hundreds of kilometers from land. All the Argonautoidea have dwarf males.

SIZE OF THE BLANKET OCTOPUS

Blanket Octopuses are known for their sexual dimorphism. Females can grow up to approximately 1 m in length (3 ft!) and have a mantle length up to 250 mm (10 inches). The males only grow up to 2.4 cm (~1 inch!) and have a mantle length to at least 15 mm (~1/2 inch!). Females weigh ~10 kg (22 lbs) and males weigh only 30 g (less than 1 lb)

BLANKET OCTOPUS LIFESPAN

The exact number of years is unknown, however, like many other octopus, this species is short lived. It is thought that males live for 1-2 years and females lives 3-5 years. Tiny males drift through the ocean seeking a mate while protecting their precious cargo (sex arm), tucked away in a sac between their funnel and right eye. Males die soon after they have found a female and detach their sex arm, which is longer than their body, inside the female’s mantle. Females will continue to live and grow for many months or years longer than the males, spawn their eggs, brood their eggs, and die shortly after the eggs hatch.

WHERE TO FIND THE BLANKET OCTOPUS

Blanket Octopuses can be found in tropical and subtropical waters. These include the Pacific, Indo-Pacific, and Atlantic oceans. Tremoctopus violaceus is frequently found in the Atlantic Ocean, Gulf of Mexico, Caribbean, and Mediterranean seas.

THE BLANKET OCTOPUS' HABITAT

The Blanket Octopus inhabits the open ocean typically at the surface or shallow coastal waters, but has been reported at a wide range of ocean depths. The Common Blanket Octopus has been observed at the surface at night and undergoes diel vertical migration. Juveniles have been collected at depths ranging from 0 to 250 m (820 ft).

BLANKET OCTOPUS DIET

Female Tremoctopus violaceus are reported to feed on pteropod mollusks and small fishes.

BODY PATTERNS AND BEHAVIORS

For the Common Female Blanket Octopus, they have a silvery tone on their sides and a dark purple or blue dorsal surface. Their ventral surface is iridescent silvery gold and the web is a deep maroon. 

The webbing or “blanket” is the most iconic and obvious feature of this group. The blanket is a web of skin that connects the long dorsal arms of the female blanket octopus. When the octopus detects a threat, she will unfurl the blanket, making her appear quite large, and scare away predators such as fishes, marine mammals, and birds. 

Males have a smooth, bowl-shaped mantle and their head is slightly wider than the mantle. The dorsal surface of the mantle and head have few scattered chromatophores. Males also have very large eyes which may help them locate a female partially by sight, but this would have to occur at a short range, relative to scale of the open ocean. It seems likely that sexes rely mainly on time and currents to bring them close enough together for visual and/or chemical cues such as females releasing pheromones.

THE BLANKET IS ONLY SEEN IN LARGE FEMALES, SO WHAT DO MALES AND YOUNG FEMALES DO FOR PROTECTION?

Males and small females (smaller than 70 mm or 3 in) carry tentacle fragments from the siphonophore Physalia spp. (blue-bottle or Portuguese man-of-war). These tentacles bear stinging cells which do not bother the Blanket Octopus. The tentacle fragments are held on the first two pairs of arms, in two rows that correspond to the two rows of suckers and may serve as both a defense mechanism and method for capturing food.

male blanket octopus Steven Kovacs

THE RELATIONSHIP BETWEEN THE MALE AND FEMALE BLANKET OCTOPUS

When a tiny male encounters a female, he inserts and detaches his sex arm (hectocotylus), that carries a packet of sperm, inside the female’s mantle. The female stores the sperm packet (this could be for months!) until she is ready to fertilize and her eggs. Female Blanket Octopuses produce 80,000-100,000 eggs and lay their eggs in a calcareous envelope (cigar or rod-shaped) which allows her to carry the eggs on her dorsal arms.

If you want to learn more about fun facts about the Female Blanket Octopus, check out this blog post to learn more about the superhero of the sea! 

https://bermudabiology.wordpress.com/2015/04/22/blanket-octopus-and-portuguese-man-o-war/

https://collections.museumvictoria.com.au/species/16366

Mangold (1922-2003), Katharina M., Michael Vecchione, and Richard E. Young. 2018. Tremoctopodidae Tryon, 1879. Tremoctopus Chiaie 1830. Blanket octopus. Version 29 March 2018. http://tolweb.org/Tremoctopus/20202/2018.03.29 in The Tree of Life Web Project, http://tolweb.org/

Jereb, P.; Roper, C.F.E.; Norman, M.D.; Julian K Finn (eds) Cephalopods of the world. An annotated and illustrated catalogue of cephalopod species known to date. Volume 3. Octopods and Vampire Squids. FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 3. Rome, FAO. 2014. 370 p

Daphne J. Fairbairn. Odd Couples: Extraordinary Differences between the Sexes in the Animal Kingdom. Princeton University Press, Apr 28, 2013. 312p

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