In the cold months of wintertime, there is nothing I like more than covering myself with a warm homemade blanket and getting cozy on the couch. Unfortunately, in the ocean, the wildlife living there don’t have such a luxury. The blanket octopus (genus Tremoctopus) is a fascinating and visually stunning species of pelagic cephalopod known for its unique appearance and remarkable sexual dimorphism. These octopuses are generally found swimming in both the subtropical and tropical ocean and living in either the open ocean or near coral reefs. 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. 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.
Habitat and Distribution
The blanket octopus makes its home in the Australian Great Barrier Reef, the Gulf of Mexico, the Mediterranean Sea, and the Indian Ocean. 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). Being nomadic creatures, they move about to different locations every couple of days. These graceful creatures can adapt to a variety of water temperatures, expanding the water they can roam in.
Physical Characteristics
Blanket octopuses get their name from sheets of webbing that stretch between some of their arms. Adult Females carry a webbing between their arms, known as a "blanket". When threatened, they stretch their arms out, creating a blanket-like silhouette meant to frighten would-be attackers away. 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. Females possess a large membrane that stretches between their dorsal and dorsolateral arms, which they can spread out to appear larger and more intimidating to predators. This cape makes the octopus appear larger and more intimidating to potential predators. Though the female blanket octopus is already large-growing to around 2 meters in length! The coloration of Blanket Octopuses can vary, often featuring iridescent blues, purples, and reds that shimmer in the light. 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. They are always in the open ocean-in the Atlantic and Pacific oceans, as well as in Info-Pacific waters-and so never rest on the seafloor. Octopuses are masters at flying under the radar, changing their coloration and texture to match their surroundings in seconds.
Size Dimorphism
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! The common blanket octopus (Tremoctopus violaceus) exhibits one of the most extreme sexual size-dimorphism known in any animal near its size or larger. Females may reach 2 m (6.6 ft) in length, whereas the males are 2.4 cm (1 inch). The weight ratio is at least 10,000:1 and can probably reach as much as 40,000:1. Female blanket octopuses weigh 40,000 times more than male blanket octopuses. The male blanket octopuses are smaller than a walnut (and do not have a cape) while female octopuses are super-sized-having one long fleshy cape that encloses their arms. The female blanket octopus can grow up to six feet in length. Males only grow up to 2.4 cm (~1 inch!) and have a mantle length to at least 15 mm (~1/2 inch!). In contrast to the females, Male blanket octopuses have a large arm in a spherical pouch modified for mating, known as a hectocotylus. 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. Why the dramatic disparity? It’s not fully known, but it’s thought that males put their energy into looking for females, not growing.
Diet and Feeding Habits
The blanket octopus roams the seas in search of food, finding a new destination every few days. The blanket octopus is carnivorous, with a diet that consists mostly of smaller fish. Octopuses are generally not picky eaters, so the ocean is one big seafood buffet for them! These are all on an octopus’s menu. You won’t find smaller octopuses going after the occasional dogfish shark - and even sometimes birds - like their larger cousins. The environment they live in also dictates what octopuses are eating. They generally are foraging and taking what they can get. Octopus species dwelling on reefs in shallow waters also make use of their excellent eyesight to track down prey. Once they zero in, they can launch a full attack, grasping prey in their web of suckers and arms. An octopus’s suckers are a powerful tool to discriminate between surface textures and shapes and let them “taste” what they are touching. With over 10,000 chemoreceptors cells on a single sucker, octopuses can lazily cruise the reef sticking their arms in rock crevices to see if anything strikes their fancy. Coconut Octopus feeds on a crab.
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Unique Hunting Strategies
This octopus has one of the strangest methods of hunting prey: using a tentacle ripped from toxic jellyfish as a weapon. Cephalopods are known for their remarkable intelligence, and blanket octopuses are no exception. They have developed an immunity to the deadly stings of jellyfish tentacles. Adult females rely on their blanket for protection, but males and young females carry weapons - Portuguese man-o’-war tentacles! And, blanket octopuses have been known to rip the venomous arms off jellyfish and Portuguese Man O’Wars to use as weapons to hunt prey. 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.
The Octo Chef
As the sun sets, most octopuses head out for the evening in search of a tasty treat. With sensitive suckers, 8 arms, and the capacity to squeeze through any space the size of their beak, not much can get between a hungry octopus and its dinner! They do, in fact, become an Octo Chef. When looking for culinary excellence in the underwater world, let Octo Chef be your guiding light. While they only prepare meals for themselves, inside their mouth are all the tools they need to craft the perfect feast. You can’t have a chef without a knife just like you can’t have an octopus without a beak! Octopuses have an underbite! Next up in an octopus chef’s kit is the radula, a tongue covered with tiny teeth used to slurp clams and mussels out of their shells once they have been broken open. These teeth move forward and back on the muscular tongue. As each row crosses the tip of the tongue the teeth become upright to cut pieces of the prey. You can estimate the size and get an approximate age of an octopus just by looking at its radula! This image shows the tooth size ranges 38 to 151 microns. To help put these numbers in perspective, the thickness of both a human hair and a standard piece of paper are 100 microns. Those are some TINY TEEF! To complete the gastronomic experience, an octopus has another tooth-covered organ called the salivary papilla that lies just below the radula. When an octopus finds a particularly delectable clam treat that it cannot wrench open with its powerful suckered arms, it uses its salivary papilla. This allows it to drill into the hard shells of clams and crustaceans. Depending on the shell thickness, an octopus can spend hours drilling (what a terrifying time to be a clam!!). When they finally make it through, they release a toxic cocktail that paralyzes their meal causing it to loosen the muscle from the shell. Chelsea Bennice, OctoNation’s lead researcher, has observed that most octopus drill holes are close to the attachment site of a clam’s adductor muscle. So, why do octopus go through all this trouble to make sure that their food is smashed, crushed, and relaxed before they eat it?
Reproduction and Life Cycle
Mating for the blanket octopus can be deadly. Mating happens at arm’s length for the four species of these cephalopods. The tiny male detaches its hectocotylus-a modified arm that holds its sperm-and gives it to the female, who keeps it in the mantle cavity until needed for fertilization. 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. The male uses up most or all of its energy to mate, breaking off its third arm in the process and sometimes dying as a result. 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. The female blanket octopus will then carry up to 100,000 eggs until they hatch. 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. When it’s time, the octopus lays upwards of 100,000 eggs, then retrieves the hectocotylus and spreads the sperm out over the egg bundle. After the baby blanket octopuses hatch, the mother will die shortly afterwards. 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. Female blanket octopuses have a lifespan of three to five years while males have a lifespan of one to two years. 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.
Defense Mechanisms
Imagine, for a moment, being a fish swimming along in the ocean. Here comes the female blanket octopus. (Watch out!) It fans out its giant cape, like a superhero or villain (depending on which one you are routing for) and wielding a jellyfish arm like a sword! Blanket octopuses spend their whole lives (3-5 years) floating in the open ocean, and, when threatened, swoop down into deeper waters with their capes flowing behind them. The blankets can be folded under the octopus’ arms to make for a faster getaway if needed. This cape can be detached when the octopus is in distress, to distract or cling to a predator. With a hydrostatic organ, the octopus can maintain depth without floating upward or sinking, so it never exhausts itself swimming.
Conservation Status
There are four known species of blanket octopuses, and all species are listed as “least concern” (population trend unknown) on the International Union for Conservation of Nature’s Red List of Threatened Species. There are no great threats to the blanket octopus. The blanket octopus is listed as least concern (population trend unknown) on the International Union for Conservation of Nature’s Red List of Threatened Species. Blanket octopuses rely on healthy coral reef ecosystems to survive. The risks these reefs face include coral bleaching and ocean acidification. It’s up to all of us to help protect blanket octopuses, coral reefs and all the animals living in the ocean.
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