mollusk of the week!

hey guys! once again i am late but it’s alright, this week’s mollusk is well worth the wait! i’m really excited for this one, so without further ado…

this week’s mollusk is: sepia officinalis, the common cuttlefish!

IT'S CUTTLEFISH TIME. this is one i’ve been looking forward to, because cuttlefish are some of the most complex and beautiful creatures in the ocean. there are several different species of cuttlefish, many of which will eventually be showcased in their own blogpost, but for now, we’re going with the most widely-recognized species as an introduction to this wonderful animal. let’s get into it!

the common cuttlefish is among the larger of the cuttlefish species, reaching around 49cm (19in) in mantle length and 4kg (8.8lbs) in weight, though common cuttlefish in subtropical seas tend to be smaller. they’re named for the cuttlebone inside their mantle, located on the dorsal (upper) side of the animal, which they can use to control buoyancy. they move through the water using the undulating fins on their mantle, but when startled, they can propel themselves with the use of a siphon inside their mantle cavity, a tube-like structure in which water enters around the sides and is then expelled to produce locomotive force. in cephalopods, the siphon is also referred to as the hyponome.

in the picture above, you can see the aperture of the siphon underneath its arms.

they are highly intelligent creatures, found to be capable of delayed gratification that we tend to see more in large-brained vertebrates like chimpanzees, parrots, and of course, ourselves! researchers at the marine biological laboratory (where the aforementioned study was conducted) note that the link between self control and cognitive ability in an animal other than primates is an incredible example of convergent evolution, where separate evolutionary histories lead to the same signs of intelligence.

here’s an interesting excerpt from the study:

“indeed, several studies have demonstrated that cuttlefish are able to optimize their foraging behaviour through learned valuation (i.e. relative values of different prey items) and by using sophisticated memory and future-oriented feeding strategies. for example, cuttlefish can remember what, where and when  components of previous foraging encounters and can quickly adjust their foraging behaviour in response to changing prey conditions by learning and remembering patterns of food availability, such dynamic feeding patterns are described as future oriented behaviours because the decision-making processes involved are influenced by previous experiences and proximate-future expectations.” (link)

cuttlefish are carnivorous, and they hunt for prey using the eight arms located around their mouth as well as two specialized feeding tentacles. their diet includes crab, shrimp, clams, snails, and sometimes even each other! though cannibalistic behavior is most often noted when there is scarce prey/mating competition, and not all cuttlefish exhibit this behavior. still pretty metal, if you ask me.

now, for the coolest part (in my opinion), lets talk about their camouflaging abilities! cuttlefish are very well known for their ability to change color very rapidly, using specialized cells like chromatophores, leucophores and iridophores to conceal themselves in their environments, as well as to communicate with other cuttlefish. they can also change the texture (!!) of their skin using peripheral muscles. if you have some time to spare, look up a video of a cuttlefish changing colors and patterns, it is absolutely mesmerizing and incredible to see.

camouflaged guys!

their eyes are also very advanced, with a unique ‘w’ shaped retina and the ability to swivel back and forth, a talent other cephalopods do not possess. though they only have one photoreceptor, their retina allows them to distinguish color wavelengths differently using polarization of light. this allows them to spot fast moving prey and hunt efficiently.

here’s a few more pictures for you guys :] aren't they just so cute?

fun fact, the color sepia is named after the cuttlefish because the reddish-brown pigment is derived from their ink! i had no clue lol.

hint for next week's mollusk: this extravagant nudibranch lets the currents carry it through the open ocean, but beware of handling it, for its venom packs a painful punch...