mollusk of the week!

hey guys, good to be back! coming back strong with one of my favorite mollusks (i know i say that every week but still :p), a beautiful and enduring bunch of cephalopods, long famed for their distinctive shells...

this week's mollusk is: nautilus pompilius, the chambered nautilus!

for a bit of history on nautiluses in general - the order nautilida began all the way back in the mid paleozoic era, around 480 million years ago, and was once a specious, diverse order with a ton of variation. unfortunately, diversity in the species declined greatly during the end-permian and end-triassic mass extinction events, and they never flourished quite the same. today, there are only nine living species in two genera, and we're only covering one today, as you read in the title: nautilus pompilius, the best-known species. having survived unchanged for millions of years, you often see them referred to as living fossils, and they certainly look the part! they're very distinct from other cephalopods, both in form and function.

these little critters are natives of the tropical pacific, and their shell size varies from about 6-8 inches (16-21cm) in diameter, with observed sexual dimorphism (females are slightly smaller than males). what sets them apart from most other cephalopods, who have internal shells, is that theirs are external, containing their soft body within. the outside of the shell exhibits countershading, something we also saw with our last mollusk - they are light on bottom to blend in with the sunlight filtering through the surface and dark on top to blend in with the darkness of the sea, shielding them from predators above and below. they possess 90 or more tentacles, more than any other cephalopod, lined with grooves and ridges rather than suckers, covered in a sticky secretion that helps them grip onto their food. much like their cousins, octopi and squid, they have a razor-sharp beak to break food apart. as far as their diet goes, they are nocturnal and opportunistic predators, eating shrimp, crab, fish, as well as detritus and carrion. 

by far, the most popular and widely recognized aspect of a nautilus is its shell, for which humans have made it into an endangered species, given its distinct spiral shape and pearlescent appearance. contrary to popular belief, their shell is actually not a golden spiral, their ratios ranging from 1.24 to 1.43, while the golden spiral's ratio is 1.618. even still, their shells have always been popular ornaments throughout history, particularly throughout the renaissance and in mid-19th century victorian era. nowadays, they are thankfully recognized as a threatened species, and international trade is restricted. 

as beautiful as they are, their shells are also extremely functional, and for more than just protection! the reason they are referred to as chambered is because the inside of their shell contains a complex system of chambers that help the nautilus move gas around to control its buoyancy. sort of like the cuttlefish, they possess a tubular organ called a siphon, which is what they use to move water and gas in and out of its cavity, as well as to propel themselves through the water. unlike the cuttlefish, however, they possess two very simple pinhole eyes which only perceive light and dark, but their sense of smell and ability to perceive depth and current directions make up for the lack of eyesight. you might be wondering how they can 'smell' without a nose - so did i - but apparently their tentacles possess chemosensory organs that can detect different scents on the ocean floor! 

so, so cool. imagine being able to smell just by touching something! actually, that sounds kind of awful now that i think about it. 

another thing that distinguishes them from their fellow cephalopods is a relatively long life-span of around 16 years, much longer than, say, an octopus or a squid. this, unfortunately, also contributes to their declining population, as they as a species cannot reproduce quickly enough to make up for the demand of their shells. this is why conservation is extremely important! i certainly don't want to live in a world without these silly guys. 

anyways, here's the gallery!

hint for the next mollusk: this cute little sea slug gained a lot of popularity online for its resemblance to an adorable mammal with big ears...