Tremoctopus (the blanket octopus) is a genus of pelagic cephalopods made up of four species. They have thin, transparent webbings between their four long arms. Females are as long as 6.6 ft and weigh up to 22 pounds, while males are one in long and weigh 15.4 grains. They are carnivores living in coral reefs. They live for three to five years, going through four life stages. They are preyed upon by large fishes and whales.
Blanket octopuses have unique features making them stand out from the already unique array of octopuses. But what are these striking features that make blanket octopuses so unique?
In this article, we cover everything you need to know about blanket octopuses and satisfy your curiosity about everything pertaining to these fantastic beasts of the seas.
Blanket Octopus Overview
Blanket octopuses are cephalopods. There are four species in the genus. They have long mantles and thin webbing between four of their arms. They swim in subtropical and tropical mid-waters. Although they are carnivores, they behave akin to prey when threatened.
|Species||Common blanket octopus, gelatinous blanket octopus, palmate octopus, Tremoctopus robsoni|
|Appearance||Capsule-like, elongated mantle, four long arms with thin, transparent webbing between them, four short arms|
|Distribution||Subtropical and tropical oceans, coral reefs|
|Life Cycle||Four stages: egg, larva, juvenile, adult. Life expectancy is between 3–5 years for females and 1–2 years for males.|
|Behavior||Curious, the first instinct is fleeing, they let their webbings out as self-defense, neutral towards humans|
|Threats||Destruction of coral reefs, predators like whales and large fishes|
The most striking feature of blanket octopuses is their eponymous blanket. The blanket itself is a thin, transparent webbing between their dorsal and dorsolateral arms. These are the two pairs of arms that are on the front of the octopus. The longer dorsal arms are in line with the octopus’ eyes and the shorter dorsolateral arms are next to them.
The blankets are used for self-defense. Although blanket octopuses are carnivores, they rarely engage in conflicts. The blankets make them appear bigger than they are, which they use to deter predators.
Blanket Octopus Classification
Blanket octopuses are cephalopods of the Tremoctopus genus. They are the only members of the Tremoctopodidae family.
Blanket octopuses are in a separate family from other octopuses. The family Tremoctopodidae only includes the genus Tremoctopus. There are four species of blanket octopuses, all of which are detailed later in the article.
|Species||T. violaceus, T. gelatus, T. gracilis, T. robsoni|
Blanket Octopus Species
There are four species of blanket octopuses: common, gelatinous, palmate, and Tremoctopus robsoni. The type species is the common blanket octopus, which is also the most widespread of the four.
The blanket octopus species are similar to each other both in appearance and behavior. Although we know about their existence, much about the four species is unknown. All strides to research blanket octopuses are fairly recent.
Even the most well-known species (the common blanket octopus) is mysterious, as researchers have only encountered a live male in 2002.
Here are the four blanket octopus species:
- Common blanket octopus
- Gelatinous blanket octopus
- Palmate octopus
- Tremoctopus robsoni
1. Common Blanket Octopus (Tremoctopus violaceus)
The most widespread of the four (the common blanket octopus) is the most well-known. Tremoctopus. They were first recorded in 1830, which is the earliest discovery of the four species.
They live in the Atlantic in shallow to mid-waters and prefer tropical and subtropical habitats.
They are also called violet blanket octopuses due to their blueish-purplish hue. Their blankets have intricate violet patterns when they are unfurled.
2. Gelatinous Blanket Octopus (Tremoctopus gelatus)
Formally described in 1977, the gelatinous blanket octopus is largely unknown. Neither its length nor its weight is known and there aren’t any pictures.
Only six young females and one female were examined live and adults were only found stranded.
R. F. Thomas (the species’ original descriptor) describes them as inhabiting the Atlantic in tropical to subtropical regions. He suspects they live in deeper waters than common blanket octopuses due to their enlarged eyes and reduced ink sac (common features among deep-water octopuses).
3. Palmate Octopus (Tremoctopus gracilis)
Unfortunately, palmate octopuses are not well-researched. It is known that they inhabit the Pacific and Indian Oceans and that they have also appeared in the Mediterranean. They live in shallow- to mid-water ranges.
The only apparent distinction between palmate octopuses and common blanket octopuses is color. The former is orangish, while the latter is violet.
4. Tremoctopus Robsoni
Also called Robson’s blanket octopus, these Tremoctopods live in the waters surrounding New Zealand. They appear to be the smallest of the four species and they have a distinct yellow-green color.
As with most blanket octopuses, the knowledge about the Tremoctopus robsoni is limited.
Blanket Octopus Anatomy
Blanket octopuses have eight arms: four long and four short. They have long, capsule-like mantles of at least 7.1 inches and thin webbing between their four long arms. Females are up to 6.6 ft long and weigh 22 pounds, while males are one in long and weigh 15.4 grains.
Blanket octopuses have one of the most extreme sexual dimorphism in the animal kingdom. The weight ratio between females and males is at least 10,000:1 and can be as big as 40,000:1.
|Blanket Octopus Appearance||Female: Long, capsule-like mantle, four long arms with thin webbing, four short arms. Males: Extremely small bodies, relatively large eyes, four longer and four shorter arms|
|Blanket Octopus Size||Female: 6.6 ft Male: 1 in|
|Blanket Octopus Weight||Female: about 22 pounds. Male: about 15.4 grains|
Although males are smaller than females, they generally look the same.
Here are the main characteristic of blanket octopuses:
- Long, capsule-like mantles
- Longer dorsal and dorsolateral arms
- Shorter back arms
- Thin, transparent webbing between the longer arms
- Vivid orange, yellow, violet, blue, and green colors
Females can be as long as 6.6 ft. Their mantle is between 7.1–9.8 in.
Males are extremely small: their total length is about one inch. This is one of the most extreme cases of sexual dimorphism in the animal kingdom.
Females weigh up to 22 pounds. Males are merely 15.4 grains on average. This is a weight ratio of 10,000:1. It is suspected that this can be as high as 40,000:1, making the smallest males weigh 3.8 grains.
Blanket Octopus Distribution and Habitat
Blanket octopuses can be found worldwide in subtropical, tropical, and Mediterranean waters. They generally prefer shallower waters, but some species can be found deeper.
Preferring a nomadic lifestyle, blanket octopuses change locations every couple of days. They are distinct from other octopuses because they don’t live in dens.
All blanket octopuses live in saline waters, like oceans and seas. All four species prefer warmer waters and live around coral reefs, but their ranges differ:
|Common Blanket Octopus||Atlantic Ocean and the Mediterranean Sea|
|Gelatinous Blanket Octopus||Atlantic Ocean and African coasts|
|Palmate Octopus||Pacific and Indian Oceans, endemic to Taiwan’s waters, appeared in the Mediterranean Sea|
|Tremoctopus Robsoni||The water’s of New Zealand|
Blanket Octopus Life Cycle
Blanket octopuses have four life stages: egg, larva, juvenile, and adult. Males live for one to two years, while females live for three to five years. They die after mating due to a phenomenon called senescence.
Blanket octopuses go through the same life stages as all other octopuses. They start their life as eggs about the size of a grain of rice and rapidly grow to be about six feet long by their adulthood.
Here are the four life stages of blanket octopuses:
Males impregnate females with their hectocotylus, an arm used for intercourse. They detach it and place it in the female’s arm.
After mating, females release thousands of eggs on the surface of protectable spaces, like crevices or the bottom sides of rocks.
Characteristics of the egg stage:
- About 0.2–0.3 in long eggs
- Resembling a grain of rice
- Milky white to transparent
- Brooding period of few months to a year (colder temperatures make for longer brooding)
After the eggs hatch, the small octopodes swim to the surface of the water to swim among the plankton.
Characteristics of the larval stage:
- About 0.2–0.3 in long hatchlings
- Resembling adults
- Called paralarvae instead of larvae
- Completely defenseless
- Feed on other larvae
- Susceptible to cannibalism (hatchlings eat each other
- Larval stage last for a few weeks to a few months
After the hatchlings developed enough, they descend into the ocean. They grow rapidly until they reach adulthood. Males barely grow at this stage, as their final length is about an inch.
Characteristics of the juvenile stage:
- Grow five percent in weight every day until they reach adult
- Constant feeding
- Lasts until the octopus reaches adult weight (a year to two years)
Adult octopuses are sexually mature and their only purpose is to search for a mate. Males become adults at 1 year, while females are usually adults at 3 years of age.
Characteristics of the adult life stage:
- Final weight and size reached
- Sexual maturity
- Nomadic, solitary lifestyle
- Maximum life expectancy: Males: two years, females: five years
Adults usually enter a life stage called senescence. This happens after mating. It is characterized by self-destructive behavior, unhealing lesions, and lack of appetite. It is a natural conclusion of the octopus’ life. Males die shortly after mating, while females live up to after their eggs hatch.
Blanket octopuses (like all octopuses) only mate once in their life and die after. Senescence is irreversible.
Blanket Octopus Diet
Blanket octopuses are carnivorous animals. They prey on crustaceans, mollusks, and smaller fishes. Some smaller individuals are known to use venomous Portuguese man o’war tentacles while hunting.
A testament to their intelligence, males and smaller females are known to use Portuguese man o’war tentacles to hunt. The man o’war tentacles are highly venomous and can easily kill smaller organisms, but it’s rarely deadly for bigger organisms (like humans). They use it both for offense and defense.
- Small fish
Blanket Octopus Threats and Predators
Habitat loss is the biggest natural threat for blanket octopuses. They are eaten by whales and large, carnivorous fishes.
Although encounters with blanket octopuses are few and far between, they are classified as “Least Concern” on the IUCN red list.
|Blanket Octopus Threats||Habitat loss|
|Blanket Octopus Predators||Whales, orcas, large fishes|
|Blanket Octopus Defense Mechanisms||Camouflage, their webbing, autotomy, ink squirting|
Blanket octopuses generally live around coral reefs, so reduction and damage in these habitats are threatening.
The threat level of habitat loss is reduced, however, as blanket octopuses are nomadic and change their location every few days. They are also highly adaptable to different temperatures.
Blanket octopuses are generally hunted by the same predators as all other octopuses. These predators include the following animals:
There is a wide array of defensive tools available for the blanket octopus, with their blanket being the most enigmatic. The webbing is only extended when octopuses are threatened. They can detach their arms as well, which still wiggle in an attempt to further distract predators. The arms grow back.
Here are the defense mechanisms of the blanket octopus:
- Ink squirting
- Venomous bite
- Usage of Portuguese man o’war tentacle
Why Is the Blanket Octopus So Rare?
Blanket octopuses are rare due to sexual dimorphism. While females can be found with the naked eye, males only grow to be about an inch long. It is hard to spot them for researchers in the waters.
Are Blanket Octopuses the Rarest Octopuses?
No, blanket octopuses aren’t the rarest octopuses. Although they are extremely elusive, the Cirrothauma magna is much rarer. It lives in the Indian, Atlantic, and Pacific Oceans. As of 2022, only four have been encountered.
Why Are Male Blanket Octopuses Smaller Than Females?
A few reasons are speculated as to why this is the case:
- Females are bigger to maintain their eggs (it requires a huge amount of energy).
- The bigger the female, the more eggs it can carry.
- Carrying sperm needs less energy.
- Being smaller means predators are less likely to notice males.
- Using Portuguese man o’war tentacles is effective against smaller animals, so males may have evolved to further utilize them.