Seeing an octopus underwater can be a very mesmerising experience. It can rapidly change body colour and texture and move with great stealth and agility, its eight dexterous arms wriggling and wiggling with uncanny independence. My reaction to seeing an adult octopus is two-parts awe and one-part fear. Being slightly wary, I always maintain a respectful distance from these three-foot-long marine molluscs. Notorious for stealing cameras from divers, spiting aquarists, swindling scientists, and most recently, punching fish — my reverence for these creatures stems from their 400 million-year-old evolutionary history.
Octopuses use their eight limbs to crawl along the ocean’s floor, sticking their arms into gaps and holes in search of food. This photograph was taken on the Andaman reefs, where the common reef octopus (Octopus cyanea) is widespread, though it is hard to conclusively identify the octopus in this frame. Photo: Tasneem Khan Cover photo: The octopus is a round-bodied, eight-armed mollusc that lives on the ocean floor. Occasionally some species step out of the sea to hunt in tidepools. Cover photo: Dhritiman Mukherjee
Masters of camouflage
Octopuses can change the colour and texture of their skin. Switching from smooth to rough, blending in with the neighbouring substrate, reef rubble or algae fronds, within seconds. They do this using their advanced sensory receptors and an army of specialised skin cells. Pigment cells called chromatophores, and reflective cells (like iridophores and leucophores) work with structural sections of the skin called papillae to change the appearance of the animal. Sometimes, sighting an octopus on the reef can be a huge source of pride, given their brilliant deception mechanisms.
Animals that belong to the phylum Mollusca, are usually characterised by a muscular body encased in an external shell as is the case of oysters, clams, and snails. Only certain molluscs have successfully discarded or internalised the shell, these include small (less than one cm) worm-like molluscs, sea butterflies, sea hares, sea slugs, and cephalopods like squids, cuttlefishes, and octopuses. The need for a shell for defence is minimised in tiny sand-inhabiting worms, distasteful molluscs, resourceful sea slugs that highjack their preys’ defences, and advanced cephalopods that can change colour, shoot ink, and escape the fight. The tasty octopus would not have lost the shell its ancestors possessed if it hadn’t acquired its impressive camouflage and the advanced neural networks to operate it.
A camouflaged starry-night octopus (Callistoctopus luteus) seamlessly blends with the ocean floor. When this octopus is threatened, it flashes white spots on its body, which is what gives it its name. Photo: Dhritiman Mukherjee (Above) Octopuses aren’t just masters of disguise, their squishy, soft bodies can fit into impossibly small gaps making them almost unnoticeable. Video: Umeed Mistry
Not just a pretty face
Octopuses are extremely intelligent creatures capable of learning new information and then applying it. While there is no set way of measuring intelligence, octopuses do have the largest brain to body size ratio of all invertebrates. But the brain only houses 10 per cent of the 500 million neurons found in an octopus’s body. Their eyes or optic lobes contain 30 per cent and the balance 60 per cent is distributed in their eight tentacles, allowing their arms to operate autonomously. This decentralised nervous system is an inspiration to robotics engineers looking for a way to optimise artificial intelligence. It is surprising how similar octopuses are to humans, considering that their last common ancestor lived 600 million years ago. The structural likeness of the eyes is a textbook example of convergent evolution. We may have evolved independently and in different time periods, but we do share similarly heightened cognitive abilities. An octopus can solve puzzles, memorise tricks, and even recognise humans. In aquariums, experiments have shown the ability of octopuses to differentiate and remember the vicious caretakers from the kind ones.
Octopuses are smart enough to use objects as tools and then store them away when not being used. They can open jar lids underwater and access food tucked away at the far ends of a puzzle. With the right amount of reward and punishment, they can even be trained to perform tricks. Training, however, does not work sometimes because of their self-aware stubborn attitude. But we can’t blame them for rebellion — as octopus research has often involved invasive treatments like mutilations and electric shock punishments. Tests of intelligence have often been derailed due to extreme non-compliance — like breaking experimental setups, causing electrical short circuits in aquarium lighting, escaping to sea, or sneaking out every night to eat fish from the neighbouring tank.
(Left) Coconut octopuses (Amphioctopus marginatus) often use abandoned coconut shells as defensive fortresses to hide in or protect themselves from predators. They also use empty clam or conch shells. (Right) An octopus peeps out of a conch shell that it has taken refuge in. Photos: Umeed Mistry
Planned parenthood
Despite their rock and roll nature, octopuses make very responsible parents. They offer the highest degree of parental care found amongst invertebrates. Males and females are solitary animals that only come together for mating. Octopuses only mate once in their lifetime, males die shortly after mating, whereas females lay the fertilised eggs inside their dens and tend to them until they hatch. Females stay with the eggs for the entire development period, keeping them well oxygenated and protected from predators. Depending on the species, this brood time can range from a few weeks to a few years, but always ends in death for the starved self-sacrificing mother.
Octopus babies hatch out looking like miniature forms of the adult, with two large eyes and eight tiny tentacles. These little ones are rather cute, and I have no problem getting close to them. In 2019, we found 33 octopus larvae over the course of our year-long weekly plankton survey in the Andaman Islands. Unfortunately, all our samples were preserved in formaldehyde and we didn’t get to witness the magic of baby chromatophores at play. What we did learn was that octopus babies are found year-round in our near shore bay and most often on new moon nights. But how these larvae sense their environment, leave the benthos (sea-bottom) for surface waters, and for what purpose, remains a mystery.
Octopuses respire using their gills located inside their body or mantle cavity. Oxygen-rich seawater is taken in by the contraction of mantle muscles. Two of their three hearts pump the blue blood across the gills in the direction opposite to the water flow, to exchange gases and other waste products. The waste carbon dioxide laden seawater is expelled out of a tube called the siphon. If the octopus does this fast and forcefully enough, it can use its siphon to move with jet propulsion. Video: Umeed Mistry
Octopuses are sentient beings capable of detailed perception and calculated reactions. Their unique personalities often win them names rather than serial numbers. Small displeasures, like stale food, can cost the aquarist a serious stare down and eye-roll from the captive creatures. Some octopuses, like Paul from Germany who accurately predicted the outcome of the 2010 FIFA World Cup, was world renowned for his oracular abilities. A recent paper in the journal Ecology detailed eight different times an octopus punched a reef fish. These fish included groupers, goatfish, and squirrelfish, and were often cooperating with the octopus on hunts. In a few cases, the octopus punched the fish to steal food, but in most instances scientists still do not know the reason behind this antagonistic behaviour. Regardless of the state of our understanding, the heightened cognitive abilities of the octopus demand respect and ethical treatment of this animal, both as a research subject and as a food resource.
