Petrified cephalopod shells were a mystery to people in ancient times and are the source of several fantastic stories. In the 600s, the town of Whitby in North Yorkshire, England, believed that ammonite fossils were snakes turned into stone, and artists often carved a snake`s head at the end of the shell. The city`s coat of arms contains three of these « snake stones ». The spherical shape of the belemnite rostrum led the ancient Greeks to believe that fossils were thrown from the sky during thunderstorms, a story that earned them the name « lightning ». They also appear in Greek folklore and are called « fingers of the devil ». With a line spanning about 530 million years, it`s no surprise that the pedigree of cephalopods is quite complicated. There are so many lineages and types of fossils that even cephalopod specialists often debate how they are related. Here are some of the best known groups of ancient cephalopods. The traditional view of cephalopod evolution is that they evolved in the late Cambrian from a monoplacophorien ancestor[114] with a curved and tapered shell,[115] which was closely related to gastropods (snails). [116] The similarity of prematurely peeled cephalopods Plectronoceras to some gastropods was used to support this view. The development of a siphoncle would have allowed the shells of these early forms to become gas-filled (i.e. floating) to support them and hold the shells vertical while the animal crawled on the ground, separating true cephalopods from putative ancestors such as Knightoconus, which had no siphoncle. [116] Neutral or positive buoyancy (i.e.
the ability to swim) would have come later, followed by swimming in Plectronocerida and finally jet propulsion in more derived cephalopods. [117] A cephalopod /ˈsɛfələpɒd/ is a mollusc of the cephalopod class /sɛfəˈlɒpədə/ (Greek plural κεφαλόποδες, kephalópodes; « Head feet »)[3] such as a squid, octopus, squid or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head and a series of arms or tentacles (muscle hydrostats) modified by the primitive foot of the mollusc. Fishermen sometimes refer to cephalopods as « squid, » in reference to their common ability to spray ink. The study of cephalopods is a branch of malacology known as teuthology. Carnivorous predators, all cephalopods have developed special tools to eat their prey. They rely on a pointed beak that cuts their prey into bite-sized pieces. Inside the beak is a tongue-shaped radula lined with tiny teeth that can push food into the digestive tract or act as a drill to drill holes in shellfish. In many cephalopods, not just the notoriously deadly blue-ringed octopus, a salivary gland produces a paralytic toxin that immobilizes and digests prey when bitten.
The cephalopods` esophagus runs through the brain and requires food to be sprayed enough to pass through the confined space. The digestive tract also includes a stomach that crushes food more and a fecal in which certain nutrients are absorbed. Ome cephalopods still have a trick up their sleeve when they change color. This is called bioluminescence, the generation of light in specialized light organs called photophores. Light is created by a chemical reaction that creates light energy in the animal`s body, similar to how fireflies flash on a hot summer night. A catalyst called luciferase triggers the light-producing substance called luciferin. The result is a strange glow, a sensational flash or a syncopated flash. A cephalopod is a strategic and cunning predator. They became skilled harassers, ambushes and masters of disguise. They are also not very picky – a cephalopod can eat anything (except plants), from crustaceans to fish, mussels, jellyfish and even other cephalopods.
Divers know that a telltale sign of an octopus cave is a collection of empty crab shells scattered on a rocky bottom. The brain is protected in a cartilaginous skull. The enormous nerve fibers of the cephalopod mantle have been used for many years as experimental material in neurophysiology; Their large diameter (due to the absence of myelination) makes them relatively easy to study compared to other animals. [13] While today`s cephalopods are best known for their many soft arms and bodies, ancient cephalopods are best known from their shells because they are well preserved as fossils. Like the living nautilus, a fossil cephalopod shell has two distinctive features: a series of chambers separated by walls but connected by an inner tube. The barriers separating the chambers are called septa and the internal tissue tube is called siphoncles. Many cephalopods are social creatures; When isolated from their own species, some species have been observed teeming with fish. [14] With the exception of Nautilidae and octopus species of suborder Cirrina,[40] all known cephalopods have an inkbag that can be used to eject a cloud of dark ink to confuse predators. [21] This bag is a muscle pouch that is originally an extension of the hindgut.