![]() "It makes them very hydrodynamic - so, very fast swimmers." While the hard shell of their ancestors has completely disappeared in octopuses, giving them amazing flexibility, the shell evolved into an internal support rod in squid, which "holds their body long and straight and is something for their muscles to work against," Staaf said. (Image credit: Getty Images) (opens in new tab) ![]() ![]() "And for octopuses, it's usually a combination of camouflage and hiding in these very tiny spaces that other predators can't fit into."Ī day octopus (Octopus cyanea) swimming off the coast of Kona, Hawaii. "For squid, that's mostly swimming very fast, although they do have some camouflage," Staaf said. But squid and octopuses don't have shells, which means they need some other way of escaping predators. Nautiluses, which have up to 90 tentacles, are protected by their hard shells, so movement isn't as critical for evading predators. ![]() Octopuses, on the other hand, have muscular tentacles that enable them to walk or crawl across the ocean floor in addition to jetting around the water column. For example, the long, narrow body shape of squid enables them to move faster than many octopus species. Depending on their muscle and body structure, some cephalopods are faster or more mobile than others. How do cephalopods move?Īll cephalopods move by filling their body cavity with water and squirting it out through a siphon, which creates a narrow jet of water that propels the animal in the opposite direction, Staaf explained. Because they are both predator and prey, "they're really central to connecting different levels of the food web," said Danna Staaf, a marine biologist and author of " Monarchs of the Sea: The Extraordinary 500-Million-Year History of Cephalopods (opens in new tab)" (The Experiment, 2020). Related: Giant squid: The real-life ocean KrakenĬephalopods are central to the health of the entire ocean ecosystem. Squid and cuttlefish eat mostly fish and crustaceans and nautilus are mostly scavengers, finding discarded pieces of other animals' prey on the seafloor, though they also hunt fish, crabs and shrimp. "Octopuses and squids live by killing and eating other animals, but because they have that permeable skin and they're really good protein, they're preyed on by almost everything else that's got teeth," Voight said. Octopuses eat everything from starfish to clams, snails, small fish and even other octopuses. Similarly, although most octopus species are solitary, at least one species, the larger Pacific striped octopus (which hasn't been formally described) form mated pairs and live in groups, and researchers have recently discovered large groups of common Sydney octopuses ( Octopus tetricus) living together, Live Science previously reported. "In shallow waters they form groups to protect themselves from visual predators, and the deep ocean means they don't have to," she said. "There are solitary squids in the deep sea," said Janet Voight, Women's Board Associate Curator of Invertebrate Zoology at the Field Museum in Chicago. Related: Octlantis: See photos of tight-knit gloomy octopus communities But as with most groups of animals, there are exceptions. Squid tend to be more social, spending time in groups that protect them from predators. Generally, octopuses tend to spend time on the seafloor and are solitary, only getting together to mate. ![]() Parts of their evolution can be trickier to track than other mollusks, due to the fact that these are soft-bodied animals that don't fossilize well.Ĭuttlefish typically spend winters in deeper waters, then move to shallow, often coastal waters to breed in the spring and summer. They all evolved from a common, hard-shelled ancestor (more similar to a nautilus). Octopuses and squid are the most well-known members of the Cephalopoda class of animals. All species of cephalopods live in saltwater environments, and while some species can tolerate brackish, or slightly salty water, none can live in freshwater. Despite having the most complex neurology of all invertebrates, most cephalopods only live for months or one to two years, depending on the species, though some nautilus can live for more than 20 years. Nautiluses have shells, other cephalopods have soft bodies covered in a tough skin. There is a wide variety of body types among the group, but the basic body plan for a cephalopod includes a minimum of eight arms, a siphon, a mantle and two eyes. The word cephalopod means "head foot" in Greek, referring to the fact that these two body parts are merged in these animals, according to the New World Encyclopedia. ![]()
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