The Creature Feature aims to introduce you to an inhabitant of the Indian Ocean. Many of
these creatures live not far offshore from some of our favourite beachside destinations. Our focus in this
article is on the cephalopods. Let’s find out a little more about them.
Whether it is being stared at by the large eyes of schooling squid in mid-water, watching the mesmerising colour changes of mating cuttlefish or playing peek-a-boo with an octopus on the reef, divers the world over consider these sightings a treat. Octopus, squid and cuttlefish are members of the molluscan class Cephalopoda and are characterized by bilateral body symmetry, a prominent head with complex eyes and tentacles modified from the primitive ‘foot’ of other molluscs. Squid and cuttlefish have eight arms and two tentacles, while octopods only have eight arms and no tentacles. This bizarre appearance, combined with nightmarish historical encounters with giant squid and gigantic octopus, has secured a colourful place for cephalopods in history, folklore and myth. And rightfully so as Cephalopoda has some incredible members in its class!
The largest known invertebrate, the Colossal squid (Mesonychoteuthis hamiltoni) is thought to grow up to 14 metres in length. The largest documented specimen, caught in 2007, weighed 495 kilograms and was 10 metres long! The Mimic octopus (Thaumoctopus mimicus) can arrange its arms and body, and simultaneously alter its colour, to mimic more dangerous species like lionfish and eels! A male cuttlefish can woo a female on his left side by changing his skin colour to a warm red while simultaneously warning another male off on his right side by flashing white! One of the largest recorded pair of eyes in the animal kingdom belongs to the Giant squid and the female Giant pacific octopus lays more than 2,00,000 eggs, watches over them till they hatch and dies soon after! The list of such incredible feats could only go on.
For divers in the shallow tropical waters around India, the more benign cousins of the Giant octopus and Giant squid add a splash of wonder to the reef. Octopuses are active both during the day and night, ‘walking’ or swimming close to the reef floor in search of food or mates. They have highly specialized skin cells called chromatophores that allow them to change colour rapidly. Their ability to change colour as well as texture contributes to their incredible camouflage, while also providing a means of communication with other octopuses. This applies to cephalopods in general. Patient divers are rewarded with the sight of amorous male octopuses attempting to woo their potential mates. As a male inches closer to the female flashing her with constantly pulsating colours, he slowly extends a specialised tentacle called a hectocotylus. With this tentacle, he passes the female a packet of sperm. If the female likes the advances of the male she will quickly, almost coyly, grab the packet and dash away into a coral recess. This little exchange along with lots of tentacle touching and cuddling is then repeated and can go on for quite some time. The female is able to store the sperm alive inside her for weeks until she is ready to fertilise her eggs with them.
These mating octopuses were photographed off South Button Island in the Andamans. The darker brown individual is the male. He spent many minutes inching closer to the female and then used a specialised arm called a hectocotylus (visible in the image) to transfer sperm packages to the female.
The body of an octopus is soft with no internal skeleton. The only hard part is its parrot-like beak made of chitin. This allows the animal to squeeze into exceptionally narrow spaces when threatened. But octopuses are highly intelligent creatures, and when not threatened, they display a curiosity that often leads to much underwater entertainment. It is not uncommon for divers hanging out near an octopus’ burrow to have the animal slowly emerge onto a nearby rock or coral for a closer look. If the diver approaches, the cautious octopus will retreat. But given time, the animal appears again, sticking its eyes out from behind a rock in what I have experienced as an entire dive worth of octopus peek-a-boo! In instances like these, it is tempting to reach out and try to touch the animal’s extremely sensitive arms. However, some species, like the Blue-ringed octopus (Hapalochlaena lunulata), possess lethal venom and most octopuses, venomous or not, can inflict a painful bite with their sharp beaks.
Squid and cuttlefish are also prolific in Indian waters and form a significant part of fishing hauls in many coastal areas. Most cephalopods have ink glands capable of releasing surprisingly large quantities of thick ink when disturbed. On the reef, schooling squid can be observed in mid-water, the fins on their mantles fluttering like translucent skirts in the sunlight. These animals, like all cephalopods, can eject water forcefully through their siphons. This jet propulsion provides them with startling bursts of speed when hunting prey or evading predators, and often a blob of ink floating in the water is the only sign that a squid or cuttlefish was in the area.
The jet propulsion provided by expelling water forcefully through the siphon (visible beneath the cuttlefish’s arms) allows cephalopods bursts of speed when hunting prey or evading predators making them the fastest marine invertebrates.
This article was first published in the April 2015 edition of Saevus magazine