The Mysterious Cuttlefish at Similan Islands Thailand


flamboyant cuttlefish Comic book writers have often looked to the animal world for inspiration when creating their superheroes. From flying to the ability to crawl up walls and throw out a web from their wrist, tiny little animals have been the source of inspiration. However, it seems no writers have looked at the mysterious cuttlefish for inspiration, because if they had, the resulting super hero would be a hero to end all other superheroes, since this small invertebrate has some truly astounding and unique features. Read along, and the next time you see a cuttlefish while diving, you will see it in a completely different light.

Biology of Cuttlefish

cuttlefish body The first thing to be noted about cuttlefish is that they are actually mollusks that belong to the order Sepiida, of the class Cephalopoda, and are therefore cousins to the Octopuses and the squids. Like the squids, they have eight arms and two tentacles that are used not only to secure prey but also to taste with. Unlike the squid which has two lateral fins at the top of its mantle, the cuttlefish has a long ribbon-like fin that surrounds the mantle completely.
All cuttlefish are venomous like some squids and some octopuses, and like the rest of the cephalopod family they all have the ability to spray out a jet of defensive ink to cover their escape as well as confuse a predator’s sense of smell.
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cuttlefish feeding
cuttlefish eye

Sexual Subterfuge

Since cuttlefish reproduction is based around large males guarding a den with a female, smaller males have to get creative if they are to succeed in mating that year. It is not uncommon for the smaller males to pretend to be females by changing their colour and hiding their extra arms in order to slip past the guard. They have even been known to pretend to be carrying an egg sac so that they can bypass the male and mate with the guarded female.

cuttelfish mating
cuttlefish eggs

Distribution and Habitat

cuttlefish distribution map Cuttlefish have quite an interesting geographical distribution; although they are warm water dwellers, they are found in tropical and subtropical locations around the world except from the Americas, where they are conspicuously absent. This old world creature is thought to have been a late developer in evolutionary terms, and as such by the time they had evolved, the Atlantic had become too deep and too cold for them to cross and reach the Americas.
Cuttlefish have a very broad and diverse depth range depending on each individual species, with some cuttlefish choosing to spend most of their time in a few meters of water, while some others can be found lurking around as deep as 600 meters.

Jet propulsion

Cuttlefish have two direct methods of swimming. While they normally use the fin that surrounds the mantel for everyday life and propulsion, when the necessity arises it goes to after burners. When it needs to escape with a big burst of speed, the cuttlefish turns on its jet propulsion systems. When in need, the creature can suck in water and use its powerful muscles to expel the water forcefully, creating its own unique form of jet propulsion.

Its own unique BCD

If you ever visit someone who has a bird as a pet, you will very likely see a small white oval shaped object at the bottom of the bird’s cage. This is a cuttlebone, given to the birds as a calcium supplement; however, it serves a very different purpose for the cuttlefish, since it acts like a Buoyancy control device. This very porous structure made of calcium carbonate is what the cuttlefish uses to control its buoyancy. It does this by controlling the gas to liquid ratio in the cuttlebone, just like a diver controls the amount of air in his BCD.

Cuttlefish: The mastermind of the Sea

cuttelfish skin For invertebrates, cuttlefish are smart. In fact, cuttlefish and their cephalopod cousins (octopi and squids) are considered the Einstein’s of the invertebrate world. With the largest brain to body mass ratio of all invertebrates, this class of mollusks have shown some amazing intelligence. They have great spatial learning and can navigate mazes, as well as developed very interesting communication techniques. Some cuttlefish can use one half of their body to send a colour-coded signal to its neighbor, while at the same time using the other half of its body to send a completely different colour-coded message to the cuttlefish on its other side. They have also evolved predation and hunting techniques to enable them to deal with their main prey, crabs, since they could pose a significant problem with their pincers and hard shells.
They are considered so intelligent that they are the only invertebrates that are protected under European union directives regarding animals used for scientific purposes.

Is it true a cuttlefish has more than one heart?

In keeping with its alien-like demeanour yes, it is true that the ever mysterious cuttlefish actually has 3 separate hearts. The cuttlefish has a heart for each of its 2 gills, and then it actually has another heart for the rest of its body. The cuttlefish uses these three hearts to pump its green blood around its body much quicker than other animals either on land or in the sea.

Which dive sites can I see cuttlefish at the Similan islands?

Richelieu Rock as a good amount of cuttlefish living their, the often mate on the east site of the rock. Koh Bon and the local wreck of Khao Lak as sedentary cuttlefish. They can be fount quite easily as well all around the Similan if you a have a good eye.

Wait a minute, did you say green blood?

Yes, absolutely. The humble cuttlefish, like a lot of aliens in science fiction films, has green blood. Most other creatures on the planet have blood that uses Hemoglobin to transport Oxygen; it is this Hemoglobin that gives their blood its distinctive and unique red colour. On the other hand, cuttlefish blood uses Hemocyanin as an oxygen transport protein, and since Hemocyanin is heavy in copper, it gives the cuttlefish blood its freaky green colour.

Can cuttlefish see behind them?

Simply put, yes. There are very few things this amazing little creature can’t do, including having a pretty much all round vision. The little critter does this with the aid of some seriously unique evolutionary adaptations. Firstly, a cuttlefish’s eye is actually the most developed eye of any animal in the world. Secondly, part of this evolution is a W shaped pupil so that even when it is focusing forward, it can pretty much see directly behind it. Scarily enough, the cuttlefish can see light polarization, and can even reshape its eye to change its focus.

cuttlefish polarized vision

What have we learned from cuttlefish?

Well interestingly enough quite a lot, and we have not just acquired some theoretical knowledge from cuttlefish but actual technological and engineering applications. By studying the change in their colour patterns, scientists have created artificial chromatophores that change colours. This has been further advanced by scientists at the University of Bristol, who have been able to create soft materials that can exhibit colour-changing behavior. This development is the start of some very interesting applications in smart clothing and camouflage.