Deep-sea mimicry —a tale of camouflage in the waters
Before taking a spoonful of the soup (read primordial, *wink*), for all the new folks out there, let’s take a sniff of the froth up top — a quick glimpse at the basics of this segment of the animal kingdom and the quirks they bring with themselves.
The phylum Mollusca is one of the most astonishing families of the animal world that despite being a non-chordate, shows diversity and variation of a wide spectrum in terms of morphology, physiology and behavioural adaptations. Broadly speaking, Mollusca can be divided into seven classes, namely —
- Gastropoda (single-shelled — cowries, cones et cetera)
- Bivalvia (two-shelled — clams, mussels et cetera)
- Aplacophora (solenogasters)
- Monoplacophora (segmented limpets)
- Polyplacophora (or Amphineura as it was earlier called — Chitons)
- Scaphopoda (tusk shells)
- Cephalopoda (nautilus, squids, cuttlefish, octopus et cetera)
Molluscs (also called mollusks) are soft-bodied, unsegmented animals, with a body organised into a muscular foot, a head, a visceral mass containing most of the organ systems, and a fleshy mantle that secretes the calcareous shell.
The word — Gastropoda — is a combination of two Greek words : Gastir which means ‘stomach’ and podi which means ‘foot’. So Gastropods can be called ‘stomach-footed’ molluscs! Funny isn’t it?
As the name suggests these have a well developed muscular foot, sometimes quite large that is used for crawling. There is a head with well developed eyes and tentacles. (observe land snails just like the one above, and you can see the tentacles coming out and going in). Except the slugs all gastropods produce an outer shell which is spirally wound. A kind of spiral coiling is seen as the animal grows. The immature organism is bilaterally symmetrical but acquires an asymmetrical shape as it matures into an adult. The coiling of the visceral mass around the central axis occurs through a process called torsion (shown in the diagram below). More on torsion in a later blog, stay tuned.
And now, let’s focus at the class Cephalopoda — where we get a myriad of the very-popular and our well-acquainted “Devilfish”. And what’s that?
You got that right — it’s the octopus!
Notable species of octopus include the Atlantic Pygmy octopus, the Blue-Ringed octopus, the Caribbean Reef octopus, the Mimic octopus, the California two-spotted octopus and many, many more.
Here, I’ll be narrowing down specifically on perhaps the most intriguing one of the list above — Thaumoctopus mimicus. Commonly known as the “Mimic octopus” it is an Indo-Pacific species of octopus famous for its capability of mimicking other local species. They are notable for being able to change their skin colour, texture, size and shape in order to blend in with their environment, such as an algae-encrusted rock, or nearby corals, through pigment sacs known as chromatophores.
But how does it do that?
Well, the Mimic octopus uses a jet stream of water through its funnel to glide over the sand while searching for prey, typically small fish, crabs, protected by its apparently Batesian mimicry of aposematic animals. It also uses aggressive mimicry to approach wary prey, for example — mimicking a crab as an apparent mate, only to devour its deceived suitor! Also, since it is able to impersonate some poisonous fish, it is at less risk of predation than others in the open. Let’s take a look now at some of the organisms that clearly have inspired this sneaky little fellow to take up pro-camouflaging!
Lion Fish
A venomous fish with brown and white stripes, and spines that trail behind it on all sides. When the octopus changes its colour, and shapes its eight legs to look like spines, it maintains a state of hydrodynamic equilibrium by keeping it’s body aligned against the frictional drag provided by the water current. The octopus floats rather than being in the substratum. It may be perceived by a potential predator as a venomous creature that should be avoided so it’s a defensive and protective measure.
Sea Snake
By waving two arms in opposite directions, the octopus succeeds in successfully mimicking the yellow and black markings of the snake. The internal body fluid volume and concentration alters by changes in osmotic gradient which gives the ability to look like the deathly sea snakes in terms of colour, morphology and even texture.
The image on the top shows a Sea snake gliding against the substratum and the image below shows two arms of Mimic Octopus. You and I should be really glad that we don’t get a terrestrial variant of this octopus!
Flatfish
By pulling its arms together on one side, and flattening out its body while moving forward along the ocean floor, the mimic octopus imitates a flatfish. It glides along the sea bed and moves like the flat fish with all arms drawn close to the body’s central axis. And last, but not the least…
Jellyfish
The mimic octopus will act as a jellyfish sometimes, by puffing up its head and siphon and letting its arms trail behind it. The octopus will then impersonate the motions of a jellyfish swimming by going to the surface and then slowly sinking with its arms spread evenly around its body; many octopus predators avoid jellyfish, and consequently avoid the Mimic octopus too.
Studies and research
Scientists do not know, for example, whether the octopus is toxic to predators. There is also conflicting research about whether its defense mechanisms are learned or inherited. Huffard and researchers at the California Academy of Sciences explored scenarios for the octopus’s behaviour and morphology.
They used DNA sequencing — both their own and that done by others — of T. mimicus and 36 related species to learn the order in which the defense traits evolved. The researchers had predicted that flatfish-like swimming was taken up, with the Mimic octopus first developing the sinuous movement of its long limbs for locomotion and then, at some later point, it probably used that movement for mimicry. Instead, they discovered that the ability to swim like a flatfish evolved along with the octopus’s very long arms.
According to DNA sequence analysis, the traits evolved in the following order:
- first came the ability to quickly change from camouflage to bold brown and white stripes, presumably to confuse a predator if camouflage failed;
- the octopus simultaneously developed its lengthy arms and its flat-fish swimming ability;
- finally, it rolled-in all these traits together — transforming to a bold colour pattern while swimming like a flatfish — when it hunts for food in the daylight, or even when resting.
And this, my dearest readers, was the story of our “underwater-chameleon”, if you will, and how she (or he) evolved, to live happily ever after.
Stay tuned for the next article to know more about such myriad diversities and amazing wonders of life under the waters (and even above)!
You stuck around till here?! — that’s amazing! I sincerely hope that you enjoyed this learning process. Chances are, that you — like me — might be into nature and life and evolution too. And for that, here are some stories I think you will enjoy!
Thank you for the read!
