The last post sparked my interest in squids, but while researching squids I found a close cousin to be even more unique! Despite its name (derived from the Old Norse word for cushion?), the cuttlefish is not something I would be too keen to cuddle with. Like squids, cuttlefish have an ink sac, which secretes a characteristically brown ink to evade predators. Historically, that brown ink was used as a dye called sepia (thank goodness we have filters to tint our photos now, right?!).
For the record, cuttlefish aren’t even technically fish, they’re molluscs.
While there are approximately 120 different species of cuttlefish, they are all characterized by the presence of a ‘cuttlebone’, which is a an internal, porous shell made of aragonite (better known as calcium carbonate). Cuttlebones are often given to caged birds such as parakeets as a source of dietary calcium.
They eat a fairly typical ocean diet: small molluscs, crabs, shrimp, etc., and they are preyed on by animals such as dolphins, sharks, fish, seals, and seabirds. Humans are also known to eat cuttlefish.
These guys inhabit shallow, tropical/temperate ocean waters ad can be found along the coasts of East & South Asia, Western Europe, the Mediterranean, and all coasts of Africa and Australia. Basically anywhere that isn’t the Americas.
Typically ranging in size from 15 to 25 cm (6 to 10 in), the largest species, Sepia apama, aka the Australian giant cuttlefish, has reached over 50 cm (20 in) in length and 10.5 kg (23 lb) is mass. See below:
Recent studies indicate cuttlefish are among the most intelligent invertebrates; they also have one of the largest brain-to-body size ratios of all invertebrates.
Enough of the not-so-interesting, here’s what make cuttlefish really cool:
They have W-shaped pupils and have 2 spots of concentrated sensor cells on the retina, one to look more forward, and the other to look farther behind. Unlike mammals who focus their vision by reshaping the eye lens, a cuttlefish changes focus by shifting the position of the entire lens with respect to the retina. Wild. Cuttlefish have no blind spot since they can see forward and behind at the same time, and though they cannot perceive colors they do have an enhance perception of contrast.
Instead of hemoglobin, red and iron-containing, cuttlefish have copper-containing hemocyanin pumping oxygen through their 3 seperate hearts (cuttlefish have 3 hearts!). This makes their blood a pretty cool greenish-blue colour.
The mating rituals of cuttlefish are pretty typical of aquatic creatures, HOWEVER, male cuttlefish avoid confrontation with other males by disguising themselves as females. They change their colouring, hide their extra set of arms (males have 4 pairs, females 3), and even pretend to be holding an egg sack.
A cuttlefish’s skin might be the coolest, and most intricate part. Like a chameleon, cuttlefish can rapidly change their skin colors. They also have the ability to change their skin texture, posture, and locomotion. All of this allows cuttlefish to communicate, camouflage, or warn off predators.
That was a lot of information to read so I’ll end this with a video showing a cuttlefish changing colours. It’s pretty trippy.