Cephalopods Cephalopods History • appeared some time in the late Cambrian several million years before the first primitive fish began swimming in the ocean • Scientists believe that the ancestors of modern cephalopods (Subclass Coleoidea: octopus, squid, and cuttlefish) diverged from the primitive externally shelled Nautiloidea (Nautilus) very early perhaps in the Ordovician, some 438 million years ago. • Cephalopods were once one of the dominant life forms in the world's oceans • Today there are only 650 or so living species of cephalopods (compare that with 30,000 living species of bony fish). However, in terms of productivity, some scientists believe that cephalopods are still giving fish a run for their money • Cephalopods are fast swimming predatory animals, extremely intelligent • Cephalopods foot is divided into tentacles – squid=10 tentacle – octopus=8 tentacle – cuttle fish=6 or more tentacle Cephalopods distinctive structures • Cephalopods have large, well developed eyes that form images • Tentacles are covered with suckers for seizing and holding prey • Cephalopods have a rasp like structure in their digestive tract called a radula for breaking down food • Cephalopods mouth has two strong beaks for tearing its prey apart. • Cephalopod is fitted with a funnel like structure that fills with water and ejects it acting like a jet propulsion More distinctive characteristics: • They are able to change multi colors • Can expand and contract pigment cells in its skin • Chromatophores(color cells) give the cephalopod the ability to change. • Can eject ink when alarmed causing the enemy to be temporarily blinded. The ink also inactivates predators chemical receptors used for detecting prey. Cephalopods diet • Feed on crabs, shrimp, fish, and other cephalopods Cephalopods Habitat • Intertidal to abyss • Polar to tropics • In other words they are found everywhere Most common Cephalopods • • • • Squid Cuttlefish Octopus Nautilus Who belongs to the group? • A cephalopod is any member of the molluscan class Cephalopoda :"headfeet". • These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. • The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea the molluscan shell has been internalized or is absent, whereas in the Nautiloidea the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites). Distribution • Cephalopods are found in all the oceans of Earth. None of them can tolerate freshwater, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay may be a notable exception in that it tolerates brackish water which has a low salinity. • Cephalopods occupy most of the depth of the ocean, from the abyssal plane to the sea surface. Their diversity is greatest near the equator (~40 species retrieved in nets at 11°N by a diversity study) and decreases towards the poles (~5 species captured at 60°N). Nervous system and behavior • Cephalopods are widely regarded as the most intelligent of the invertebrates and have well developed senses and large brains. • The nervous system of cephalopods is the most complex of the invertebrates. • The giant nerve fibers of the cephalopod mantle have frequently been used as an experimental material of neurophysiologists for many years; their large diameter (due to lack of myelination) makes them easier to study. • Cephalopods are social creatures; when isolated from their own kind, they will take to shoaling with fish. • Some cephalopods are able to fly distances up to 50 m. While the organisms are not particularly aerodynamic, they achieve these rather impressive ranges by use of jetpropulsion; water continues to be expelled from the funnel while the organism is in flight. Senses • Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of chemical sense organs. Octopuses use their tentacles to explore their environment and can use them for depth perception. Vision and hearing • Most cephalopods rely on vision to detect predators and prey, and to communicate with one another. Consequently, cephalopod vision is acute. • Surprisingly—given their ability to change color—all octopuses and most cephalopods are color blind. When camouflaging themselves, they use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background may come from cells such as iridophores and leucophores that reflect light from the environment. They also produce visual pigments throughout their body, and may sense light levels directly from their body. Vision and hearing • Unlike many other cephalopods, nautiluses do not have good vision; their eye structure is highly developed but lacks a solid lens. They have a simple "pinhole" eye through which water can pass. Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, as well as locating or identifying potential mates. • Cephalopods can use their statocyst to detect sound Use of light • Most cephalopods possess chromatophores - that is, coloured pigments - which they can use in a startling array of fashions. • As well as providing camouflage with their background, some cephalopods bioluminesce, shining light downwards to disguise their shadows from any predators that may lurk below. The bioluminescence is produced by bacterial symbionts. • Bioluminescence may also be used to entice prey, and some species use colorful displays to impress mates, startle predators, or even communicate with one another.It is not certain whether bioluminescence is actually of epithelial origin or if it is a bacterial production Body color • Coloration can be changed in milliseconds as they adapt to their environment, and the pigment cells are expandable by muscular contraction. • Coloration is typically more pronounced in near-shore species than those living in the open ocean, whose functions tend to be restricted to camouflage by breaking their outline.