Whereas the gastropod means stomach on the foot, cephalopods mean the head on the foot, but with these mollusks, the pod (foot) has evolved into numerous retractable arms/tentacles, which may be equipped with suction cups, hooks, or sticky mucus to catch the prey and perform other functions. Yes, we’re talking about octopus and squid, and their close cousins, the nautilus and squid. Most cephalopods have eight to ten arms, but some (such as the nautilus) have as many as 90. Now that’s a lot of hand washing!
If you look at bivalves and cephalopods side by side, you would never have imagined that they were in the same family. Not even close! Each cephalopod has a well-developed brain, three hearts, good eyesight, jet propulsion system, pre-grabbing arms, a sharp beak, and (in most species) an ink sack for self-defense – while the clam is a piece of meat sealed with a shell They can stick to rocks and sip through straws.
Most cephalopods lack the distinctive shell of most mollusks. One exception is the Nautilus chamber, which has a sophisticated shell with chambers filled with air to keep it afloat. Squid, which looks a bit like a nautilus without an outer shell, has an oblong, saucer-shaped inner shell called a squid bone, which is often sold in pet stores as a source of calcium for birds (which seems a bit wrong, btw). Squids have a long, thin inner shell called a pen.
In this article, we introduce you to the four most common members of the cephalopod family.
octopi
If aliens exist on this planet, they are an octopus or an octopus (by the way, both spellings are acceptable). Octopuses are among the most intelligent creatures in the sea, and the most intelligent invertebrates on Earth thanks to their large brain. In fact, the brain-to-body ratio of an octopus is the highest among all invertebrates and greater than that of many vertebrates. It even has a set of nerves that serve as the brain for each arm, enabling the octopus to move them independently. The octopus is also a tool user and can learn and remember. (Full disclosure, it’s Philip’s favorite animal – can you tell?)
Moving to the body, the octopus has eight arms, each with two rows of suckers used to capture and hold prey and to stick to smooth surfaces. The arms lead to a skirt with a mouth (beak) in the middle. With three hearts, they have a lot of love. One heart pumps blood through the body, while the two smaller hearts pump blood to the gills. Their bodies are very flexible, allowing them to squeeze into very tight spaces – as long as their beak fits them, they can make it up, bringing a whole new meaning to the phrase “if I fit, I sit.”
Compared to bivalves, their sex life is very conservative. Males remain males and females remain females throughout their lives. Once the male transfers sperm to the female to fertilize her eggs, the female becomes a devoted and tough mother. . . literally. For example, the mother of the giant Pacific octopus lays her eggs and watches them attentively, keeping them clean, ventilated and sheltered for up to ten months, during which time she does not leave and does not eat. They usually die soon after their eggs hatch. Octopus parents aren’t much better off – they often die after mating (talk about dead parents!).
The octopus will always beat you in a game of hide and seek. They are able to change their color and texture to match their surroundings to a T. But the imitation octopus makes everyone stand out; It can even change its shape to impersonate other creatures like flounder, lionfish, eel, or even a tube worm. Hi, do you guys rent out for parties?
Honestly, we could write an entire chapter or even an entire book on the octopus, given how adorable it is. Just take a look at how awesome the dumbo octopus is, and the mating rituals of the Argonaut Octopus is something we can’t talk about in a book for fans of the masses. So much to say, but so little time.
squid
Squids look a lot like an octopus, but they’re different in many ways, including the following:
Octopuses are smarter than squid, but squid are better swimmers.
Octopuses have a round body, rectangular pupils, and eight arms, while squids have a triangular body with a fin on both sides, round pupils, eight arms, and two longer tentacles (with suction cups at the ends only).
Octopus arms are more flexible than squid arms, enabling them to walk around and hold and move objects.
The squid has a solid internal structure, called the stylus, that runs along the mantle and provides support; Octopus does not.
Octopuses generally hang out on the sea floor eating crustaceans and other benthic prey, while squid prefer the open ocean, feeding on shrimp and small fish.
The squid’s self-defense mechanism involves expelling a cloud of ink that acts as a smokescreen, while the octopus relies more on camouflage or pressing its body into a hollow body or crevice, although in desperate situations the octopus can also ink.
Octopuses breed as a partner and care for their eggs for up to a year until they hatch, while squids mate in large groups and leave their fertilized eggs attached to rocks or coral to fend for themselves.
Octopuses are generally solitary, while squid may live alone or in groups.
Squids range in size from about 16 millimeters (less than one inch, and so cute) up to 22 meters (about 72 feet, and terrifying) when stretched out.
Some cool species of squid include the glass squid — almost fully transparent except for its eye balls (though its eye lids act as an invisibility cloak); the vampire squid, which can turn itself inside out to avoid predators; and the Humboldt squid, which can pulse its body with flashing red and white bioluminescence. Yowsa!
Giant squid
The giant squid is about eight meters (26 feet) long, but with its tentacles stretched out, it may reach 22 meters (72 feet) in length. These massive creatures live in the deep ocean, and scientists still don’t know much about them. Most of what’s known has been gathered from studying carcasses that have washed up on beaches or been brought in by fishing boats.
Based on the limited information available, we know that they eat shrimp, fish, and other squids. We also know that they engage in defensive epic battles with whales and sharks (that like to eat squid), based on the fact that whales and sharks have been observed with what look like giant squid hickeys all over them.
Because they live in the deep sea, giant squid have giant eyes. We’re talking BIG, as in largest in the animal kingdom — about 10 to 12 inches in diameter (the better to see you with my dear!). Researchers also think that giant squid live only about five years, meaning they must grow like weeds, and that they mate only once, so they’d better make it count.
However, while the giant squid may be the longest, it may not be the largest. The colossal squid is shorter but weighs twice as much. One colossal squid on display at the Ta Papa Museum of New Zealand tips the scales at 490 kilograms (just over 1,080 pounds) while an average Giant Squid weighs in at around 275 kilograms (606 pounds). The beak of the colossal squid is the largest of all among mollusks, and their eyeballs are about the size of soccer balls.
Even with their massive size, the giant and colossal squid are the preferred prey of the deep diving sperm whale. And (fun job), some scientists study the undigested beaks of these squid in sperm whale stomachs to gather additional information about the species. That would be one colossal and very smelly day at the office.
Cuttlefish
Cuttlefish, also known as cuttles (no, not cuddles, although they look kind of cuddly), are sort of a cross between a squid and an octopus but with a more compact body. Like an octopus, a cuttlefish has a big brain and is a master of camouflage. Like a squid, it has eight arms and two longer tentacles and its head and body are tapered, more like a torpedo. Cuttlefish are unique in that they have an undulating fringe running along their sides and a cuttlebone to help with buoyancy, which enables them to hover. Another unique feature is their pupils, shaped like a “W,” which enables them to see in front of and behind them at the same time.
They tend to live in deep water during the winter and in shallow water during the summer months, and they only live a year or two, dying soon after mating.
Giant squid lives in the waters around Australia. This large weed can grow to be about 50 cm (20 in) tall and weigh about nine kilograms (about 20 pounds). That’s a lot for cuddling! Each season they return to the same rocky shores in southern Australia, mate, lay eggs, and then die. When the next generation hatches, they head out into the world (not much is known about where they go or what they do), but they always return to the same area to mate, lay eggs, and die (cue the “Circle of Life” from The Lion King).
nautilus
If a snail, shrimp, and octopus had a baby together, it would look like a nautilus. The nautilus has a spiral shell like a snail, but it is divided into chambers that contain air to make the nautilus buoyant, enabling it to float in water. As the nautilus grows and expands its shell, it creates new chambers. It has a face like a shrimp and arms like an octopus – in fact about 90 bundled tentacles and secrete mucus to catch food and cling to stationary objects when at rest. Compared to the octopus and squid, the nautilus does not have the greatest vision, relying more on the sense of smell to find food.
They are nocturnal (active at night), making daily migrations up and down the water column. They live much longer than other cephalopods (up to 20 years). Unfortunately, their shells are highly prized and because they do not reach sexual maturity until they are 10 to 15 years old (and even when they do, females only lay about ten eggs maximum), their populations have decreased dramatically and they will need a long time to recoup. Because they need a hard crust to survive, they are also under threat from ocean acidification. Fortunately, it is a protected species, although poaching continues to occur.
The nautilus is considered a living fossil, because it hasn’t changed much over the 500 million years that it has been (in some form). Today, they live in the waters of the Indo-Pacific, hovering over coral reefs at depths of about 100 to 300 meters (330 to 990 feet). They can’t go deeper, because the pressure will crush their air-filled shells. Not a good way to go.