Often, cephalopods are voracious consumers. A study of the California two-point octopus found that an 80% decline in the octopus population triggered a 500% explosion in their prey populations, gastropods (snails and snails) and hermit crabs. In the English Channel, unusually warm waters in 1900 and 1950 caused an “octopus plague” in which Octopus vulgaris, an unusual species in the region, became so abundant that they consumed a large part of the crustaceans. The Western Evening Herald of Plymouth, United Kingdom, wrote in 1899: “They have pretty much ruined fishing, and many men have desperately hung up their boats. They devour everything, even crabs, lobsters, oysters and all crustaceans. Intelligence requires big brains. A cephalopod brain is divided into many different sections called lobes. Loligo squid has at least 30 different lobes. Lobes are specialized centers that, among other things, process information from the eyes, control camouflage and store memories. Although structured in the same way as other molluscs, a cephalopod nervous system far outperforms the nervous system of its closest mollusc relatives – the California sea snail has about 18,000 neurons, while the common octopus, Octopus vulgaris, has about 200 million neurons in its brain. Humans have many more, just under 100 billion, but a cephalopod is on par with dogs and some monkeys, as they also carry about two-thirds of their neurons in their arms, not their heads.
Unlike humans and other mammals, the brain of the cephalopod grows by one and a half times its original size from the time of birth to adulthood. The ink can also serve as a warning to other cephalopods. In the presence of ink, the squid from the California market will begin to swim, and the Caribbean reef squid will begin to color the camouflage. The Japanese dwarf squid figured out how to use ink to hunt shrimp instead of just hiding from predators. He splashes a few quick puffs towards the shrimp, then whistles through the ink to catch his meal. The ink can be used both to hide from the prey and to distract shrimp from noticing the incoming attack. Despite the complexity of their eyes, cephalopods are most likely colorblind. The ability to see color depends on the specialized receptor cells. In animals and humans, these cells are called cones, a difference from light-sensitive cells called rods. Humans have three different types of cones: one that detects red wavelengths of light, one that recognizes blue, and one that recognizes green. In combination, these cones allow us to see a wide range of shades.
But cephalopods have only one type of photoreceptor cell, which makes them colorblind. Combined, these color and texture change techniques allow a cephalopod to mimic almost any background. Roger Hanlon`s experiments show squid that skillfully imitate speckled textures, stripes, spots and a black and white chessboard! Rodhouse, P. G. K., Pierce, G. J., Nichols, O. C., Sauer, W. H. H., Arkhipkin, A.
I., Laptikhovsky, V. V., et al. (2014). Environmental Impacts on Cephalopod Population Dynamics: Impact on Fisheries Management. Adv. Mar. Biol. 67, 99–233. doi: 10.1016/B978-0-12-800287-2.00002-0 People have loved to eat cephalopods since ancient times. According to Paul Bartsch, curator of molluscs at the Smithsonian Museum of National History in the early 1900s, Greeks and Romans considered all kinds of octopus to be a delicacy. In Rome, they stuffed the cavity into the body full of spices, cut off the arms and baked it into a cake.
During the preparation, the cooks refused to use iron knives, claiming that the metal left an unappetizing taste and would instead use special bamboo knives. The Greeks also enjoyed octopus and often sent one as a gift to parents on the fifth day after the birth of a child, on the day of baptism. A comic Greek story tells the story of Philoxene of Kythera, a particularly greedy man. One evening, Philoxene wanted an elaborate meal, which then included a massive three-foot octopus as the main course. After eating all eight arms alone, the man became ill and needed the attention of a doctor. But the doctor`s prognosis was not good – Philoxena was informed that he had only a few hours to live. He resigned himself to his fate and decided to finish the rest of the meal, saying, “He left nothing on earth that seemed worthy of regret.” With eight arms lined with suction cups and, in some cases, a pair of tentacles, a cephalopod can maintain a fairly firm grip. But the way a cephalopod maintains this grip is different between squid and octopus. Squid use their suction cups mainly to catch food. The cup-shaped nipple connects to the squid`s arm or tentacle via a thin stem. As soon as the rigid, circular surface of the vacuum cleaner comes into contact with the prey, a pull of the rod reduces the pressure in the suction cavity and creates a sticky seal.
For cephalopods, the term “blue blood” has a more literal meaning than the medieval reference to nobility – their blood is actually blue. While humans and other animals depend on an iron-based oxygen transport system, cephalopods have developed a copper-based system that is the source of the blue color (similar to horseshoe crabs). The copper-based molecule in a cephalopod`s blood is called hemocyanin, which binds to oxygen to transport it through the body and muscles. It has significantly lower oxygen binding power than iron-based hemoglobin, although a study on an Antarctic octopus, Pareledone charcoti, suggests that the hemocyanin system helps cephalopods maintain efficient oxygen transport in environments with varying temperatures and oxygen levels. Hemocyanin is more effective in cold water, but loses its oxygen retention in more acidic water, suggesting that as the oceans become warmer and more acidic due to climate change, cephalopods may struggle to get enough oxygen into their bloodstream. Carnivorous predators, all cephalopods have developed special tools to eat their prey. They rely on a sharp beak that cuts their prey into bite-sized pieces. Inside the beak, a tongue-shaped radula is lined with tiny teeth that can push food into the digestive tract or act as a drill to drill holes in crustaceans. In many cephalopods, not just the notoriously deadly blue-ringed octopus, a salivary gland produces a debilitating toxin that immobilizes and digests prey when bitten. The esophagus of cephalopods passes through the brain, so food must be sprayed enough to fit through the narrow space.
The digestive tract also includes a stomach that further purees food and a cecum, in which certain nutrients are absorbed. The story of the birth of the name Hectocotylus is a story of false identity. In 1829, the famous naturalist George Cuvier identified a strange “organism” in the mantle of a female paper nautilus (which, to make things even more confusing, is actually an octopus) and thought it was a new parasitic worm he called the hectocotyl. It turned out that it was actually a male cephalopod arm, but the name stuck.