Coconut Octopus

Jun 28

Amphioctopus marginatus

The coconut octopus carries seashells or coconut shells beneath its arms as it travels — using a few of its arms to hold the shells and the others to walk awkwardly along the sea floor. If this octopus encounters danger, it assembles the shells around itself, forming a kind of armour.

Invertebrate Intellect

Of all the invertebrates, few have such a reputation for intelligence as the octopuses.¹ The common octopus, the most studied of the bunch, is one of the brainiest animals in the sea. It can solve puzzles, recognize human faces, and skillfully contort its body — earning it a reputation as a notorious aquarium escape artist. Many octopus species are masters of camouflage, none more masterful than the mimic octopus. Using the colour-changing cells (chromatophores) that cover its skin and its nimble flowing arms, it can mimic up to 15 different marine animals, from venomous lionfish to slithering sea snakes, floating jellyfish, and scuttling crabs. Other octopuses use intimidation to frighten foes, such as the California two-spot octopus, with two bright blue spots on its body that appear like staring eyes. The blue-ringed octopus is completely covered in such markings and, because of its venom — one of the most potent toxins on Earth — it's simply left alone by most other animals.

The octopuses, of which there are around 300 species, belong to the group known as molluscs; a large phylum that includes snails and limpets, clams, oysters and mussels, chitons and tusk shells, as well as the octopuses' closest relatives, the squids and nautiluses. The majority of molluscs grow their own protective shells, in which they lie safe for their entire lives. Most octopuses do not.² But one species gets around this physiological limitation by employing its intellect to craft its own shell.

The Crafty Cephalopod

The coconut octopus typically displays a vein-like pattern on its skin.

The coconut octopus lives in the shallow coastal waters of the tropical Indian Ocean, making its home on the sandy sea floor where it feeds on fish and shrimp. Its skin is decorated with dark vein-like patterns — another name for the species is the 'veined octopus' — and its eight arms are each lined with 150 suckers that occasionally seem to glow a bright blue. Like all octopuses, it can change its colour using the chromatophores that cover its skin, but its camouflage is far from that of the mimic octopus. It lacks any intimidating eyespots or toxins of any kind, and, at a length of around 30 cm (11.8 in), it's far from the largest octopus.³ In an aquatic world of hungry sharks and larger octopuses, the coconut octopus uses its ingenuity to survive.

As it roams the sea floor, it searches for suitable seashells or halved coconut shells. Upon finding some to its liking, it stacks the shells up and places them under its arms — like a person carrying barrels. With some of its arms occupied with holding the shells, the octopus must engage in a form of bipedalism; strolling somewhat awkwardly along the sand on two stilt-like arms. It travels in this way for considerable distances (for a creature of its size), "walking" for 20 metres (65 ft) at a time with its shell collection tucked beneath its arms. The shells may be a burden to it now, but they can quickly become lifesaving tools. If the octopus encounters any kind of danger, it assembles its shells into an armour around itself, protecting its squishy body from any attacks.

A coconut octopus carrying a clam shell for shelter.

Tool use was once lauded as the milestone by which we measured intelligence — a cognitive feat that only we Homo sapiens were capable of. This proved to be very wrong. We discovered that plenty of crafty creatures, from distant corners of the animal kingdom, showed this ability, from chimpanzees and elephants, to crows and shrikes, to octopuses. The coconut octopus's protective form of tool use involves choosing to carry tools in a non-functional form — an effort that clearly hinders the octopus's locomotion abilities — and then knowing how to put together the separate parts into one functioning tool when it's needed. This behaviour likely began with an octopus finding and using large empty shells from mussels or clams, which naturally come in form-fitting pairs, and was then adapted to exploit human scraps; halved coconut shells discarded by coastal communities.

A Dangerous Affair

But there is one perilous circumstance in which this octopus cannot defend itself with its make-shift shell armour. Mating is a dangerous affair for a male. He must deliver his sperm packet to the female's mantle with an arm specialized for the task, but he mustn't dawdle. Once the package is delivered, we will attempt a swift escape, but the female may pull him into a complex mating ritual. If she is successful, this dance may be the male's last, for, in the end, he will likely be strangled and devoured — valuable energy for the 100,000 eggs the female is going to lay.

¹ The word 'octopus' is a Latinized form of the Greek word 'októpus' and means “eight foot". There are three plural forms of the word. 'Octopi' is the oldest of the three and gives the plural form a Latin ending. 'Octopuses' gives it the typical English ending of a plural form. The last, and least used, plural form of octopus is 'octopodes', using a Greek ending. I opted for octopuses, even though I'll admit that 'octopi' rolls more nicely off the tongue.

A female argonaut with her paper-thin shell.

² There is one group of octopuses that do have true outer shells — half of them do, at least. These bizarre octopodes are called the argonauts and there are some four to six unique living species. They are some of the very few pelagic octopuses; rather than skulking around shallows and reefs, they travel the open oceans. The argonauts exhibit extreme sexual dimorphism. The female grows to about 10 cm (3.9 in) with a shell of up to 30 cm (11.8 in). The male is shell-less and rarely gets bigger than 2 cm (0.8 in).

Unlike the rock-hard protective shells of other molluscs, the shell of the female argonaut is paper thin and spiralled — hence why these octopuses are sometimes called ‘paper nautili’. The female's shell actually serves as a kind of incubation chamber for her eggs. The singular purpose of a male argonaut is to fertilise the larger female's eggs, and he does so by handing over a sperm packet using a special arm called the hectocotylus. But rather than just handing it over, he detaches his entire arm (when human naturalists first saw this arm attached to a female argonaut, they believed it to be a parasitic worm). Once the male has handed over his seed, he proceeds to die.

Th giant Pacific octopus (*Enteroctopus dofleini*) is the largest living octopus species,

³ The largest living species is the giant Pacific octopus. From the tip of one arm to the tip of another, it can grow to be 9 metres (29.5 ft) long and weighs 20 kg (44 lbs).

**Where Does It Live?**

⛰️ Warm tropical waters, typically in shallow sandy areas.
📍 Throughout the western Pacific and part of the Indian Ocean. ¹

‘Least Concern’ as of 21 July, 2014.

IUCN

Size // Small
Length // 10 cm (4 in) mantle and 30 cm (12 in) total length
Weight // 400 grams (0.9 lbs)
Activity: Crepuscular 🌅
Lifestyle: Solitary 👤
Lifespan: 3 - 5 years
Diet: Carnivore
Favorite Food: Shrimps, crabs, and clams 🦐
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Family: Octopodidae
Genus: Amphioctopus
Species: A. marginatus

Another name for the coconut octopus is the 'veined octopus' because of the dark vein-like patterns that can be seen covering its skin most of the time.

Each of the coconut octopus's eight arms are lined with 150 suckers.

While carrying its shells, it walks along the sandy sea floor in a bipedal way, on two of its arms — travelling up to 20 metres (65 ft) at a time.

The coconut octopus's unique behaviour likely began when it discovered that it could use mussel or clam shells to protect itself. Once humans began to throw their leftovers into the sea — halved coconut shells — this octopus took advantage to scavenge a new type of armour.

A male octopus has a specialised arm for delivering his sperm packet to a female. The male coconut octopus must do so quickly, for a female may strangle and devour him.

A female coconut octopus can lay upwards of 100,000 eggs.