We were fortunate to go on two night dives while at Taveuni Island with Susan from ‘Wiz’. On our second night dive, a few nights ago, Susan started madly flashing her torch to get our attention, and there before us was a weird creature about 30 cm long and hovering over the reef. At first, I thought it was an octopus with its legs tucked in but then guessed it was a cuttlefish.
Despite being called a cuttlefish, it is not a fish but rather a type of mollusc known as a cephalopod and closely related to the octopus, squid and nautilus. Like that of an octopus the cuttlefish also has eight arms. The really weird thing we noticed about the cuttlefish is the fin which resembles a short, flouncy skirt that flaps around the body. The fin manoeuvres the cuttlefish forward, backward and even in circles, as you can see in the video below.
You can see the fin on the underside of the cuttlefish that glows blue in the photos above that Tristan took.
In photo on the left surrounding the body you may be able to see the very thin fin, it looks slightly blurry as it was flapping while the photo was taken. Photo 2 shows the cuttlefish’s eight arms.
Well you may not have seen one in the sea before, but chances are that if you have ever walked on the beach you may have seen the remains of one washed up on the sand. I can remember seeing them on the beach when I was young and we would take it home and put it in the cage for our cockatoo. The cuttlefish bone is rich in calcium which is why it is often sold in pet stores for birds as a nutritional supplement. In fact the cuttlefish bone controls the animals buoyancy by adding different amounts of liquid or gas into it which allows them to move up or down.
Have you ever seen one like this on the beach?
Both octopus and cuttlefish are masters of disguise. Cuttlefish can change not only their colour and pattern but also the texture of their skin, as their skin possesses up to 200 pigment cells per square millimetre. Also like the octopus and squid the cuttlefish too has an ink sac which it can use to deter predators. No, we did not see the cuttlefish shoot any ink. The purpose behind the colour, pattern and texture change are for the cuttlefish to evade or deter predators or to mimic other species to help them catch their prey or to communicate with other cuttlefish.
Can you see the nodules on the cuttlefishes body that allows it to blend with the coral behind it, pretty cool right?
Look how its changed colour and pattern to blend with it’s surroundings.
Interestingly enough, although the cuttlefish have highly developed eyes with the ability to reshape its eyes, it is in fact colour blind. The cuttlefish’s eyes are not only very large in comparison to its body but the pupils are in a W shape.
We think that this particular cuttlefish belongs to the species known as the broadclub cuttlefish which is found in both the Indian and Western Pacific Ocean. It is the second largest cuttlefish species reaching up to 10 kg.
Some interesting facts about cuttlefish:
- The female cuttlefish dyes her eggs black using her ink and they resemble a grape. The eggs are sometimes called sea grapes.
- Like the octopus, cuttlefish have three hearts and blue blood.
- Cuttlefish have a relatively short life span of only 1 – 2 years.
- Cuttlefish can use jet propulsion to move quickly by filling their body cavity with water and then squirting it out, which will propel them backwards.
- The cuttlefishes’ brain to body size ratio is one of the largest of any invertebrate, perhaps even larger than the octopus.
Information on the cuttlefish came from the following sites: