Biology Cuddlefish and Camouflage - Essay Example

Biology - Cuttlefish and Camouflage Cuttlefish is not a fish; it is a cephalopod. The cephalopods are a highly developed of the mollusks. The molluskan foot is modified in the cephalopoda into characteristic organs, the funnel and arm. They are exclusively marine animals, most abundantly found in shallow coastal areas. Belonging to the Order Sepioidea, cuttlefishes have been in existence worldwide, with family exceptions, since the Tertiary Period (65 to 1.8 million years ago). They are distributed around the globe, and currently, over 120 unique cuttlefish species are known, none of them endangered, while new species continue to be identified (Animal Guide, www.pbs.org). Cuttlefish have a short life span and a high growth rate. They are active swimmers with a predatory lifestyle, feeding largely on crabs, prawns and fish. Anatomy: 1. Arms, tentacles and beak Cuttlefish possess eight forward-reaching arms specialized to grasp the prey after it has been captured using an additional pair of elongated tentacles (Chaddha, 2007) with a single suction cup at each tip. In the middle of the eight arms, there is a small beak, which cuttlefish use to break open the shells of mollusks, crabs, and other crustaceans (Animal Guide, www.pbs.org). According to Chaddha, “The arms are also important for a defensive display in which the cuttlefish sucks water into its mantle cavity and spreads its arms in order to appear larger to its potential opponent.” (2007). 2. Brain. Like all cephalopods, cuttlefish possess a highly developed central nervous system with a well-defined brain. Their brain-to-body size ratios are the highest among all invertebrates. “The cuttlefish brain can handle input from a variety of senses, including sight, smell, and even ‘sound’ (in the form of pressure waves).” (Chaddha, 2007). 3. Cuttlebone. The internalisation of the shell that occurred with evolution in the cuttlefish has helped them to become efficient swimmers. The internal shell of a cuttlefish, called the cuttlebone, retains air spaces and controls buoyancy making it functionally equivalent to swim bladders in fish (Chaddha, 2007). It also prevents them from colonizing the deep oceans since the pressure would cause a gas-filled shell to implode. 4. Eye. The cuttlefishes have the most highly developed eyes in the animal kingdom. They “can see well in low light and can also detect polarized light, enhancing its perception of contrast. While we humans reshape our lenses in order to focus on specific objects, the cuttlefish moves its lenses by reshaping its entire eye. Also, the cuttlefishs eyes are very large in proportion to its body and may increase image magnification upon the retina, while the distinct "W"-shaped pupil helps control the intensity of light entering the eye.” (Chaddha, 2007). 5. Lateral lines. Cuttlefishes cannot hear. They can detect sound in the form of pressure waves using the lateral epidermal lines consisting of thousands of hair cells. The hair cells are useful in defense too, as they allow cuttlefish to detect the movement of possible predators. 6. Hearts and Blood. Cuttlefishes have two hearts to pump blood to its large gills and one heart to circulate the oxygenated blood to the rest of its body, that is, a total of 3 hearts. The blood contains hemocyanin, a copper-containing protein for oxygen transport; hence, it is green in color. 7. Ink sac. Cuttlefish produce a brownish ink, which they discharge to confuse predators when threatened. 8. Reproduction. At mating, the male transfers its spermatophores into the female’s buccal area (which is a part of the mouth) where they are stored until the female is ready to fertilize her eggs with them. He female deposits her eggs in locations such as under rocks and uses her arms to spread the stored spermatophores over each egg. 9. Skin. The cuttlefish beats the chameleon hollow in changing skin colors. When competing for a mate, the skin of the male is known to take on hues and stripes similar to a zebra. “…..cuttlefish use their powers of transformation for more than just camouflage.” (Lewis, 2007). Color change and Pigments Over millions of years of evolution, animals have developed numerous ways of defending themselves against predators. The cephalopod ancestors of the cuttlefish possessed an external shell that helped to protect them from predators. However, the internalization of the shell in modern cuttlefish has deprived them of this armor against predators which include sharks and dolphins. They have other defense mechanisms at their disposal to ward off predators, the most important of them being cryptic coloration or in layman’s language, ‘camouflage’. The cuttlefishes are masters of disguise having the unique ability to change their color and shape at will instantly, to blend into their surroundings so their presence might go undetected by predators. The patterns and colors assumed by the cuttlefish are produced by different layers of cells stacked together. Various combinations of cells operating at any given time enables the cuttlefish have such a large repertoire of patterns and colors (Wood and Jackson, 2004). The most important of these cells are the chromatophores located directly under the skin of the cuttlefish. The chromatophores are cells that consist of an elastic saccule containing a pigment and attached to 15-25 muscles. Each chromatophore is also attached to a nerve ending; thus, the chromatophores are neurally controlled. According to Wood and Jackson, “When the muscles contract, they stretch the saccule allowing the pigment inside to cover a larger surface area. When the muscles relax, the saccule shrinks and hides the pigment.” (2004). By increasing the size of one saccule while decreasing the size of another one located next to it, complex patterns (e.g., zebra stripes) are produced (Messenger, 2001). The pigments in chromatophores can be black, brown, red, orange or yellow but not blue and green. Another type of cells, iridophores, are stacked immediately below the layer of chromatophores. They produce the metallic greens, blues and gold colors as well the silver coloration sometimes seen around the eyes and ink sac. The iridophores are not neurally controlled but are controlled by specific hormones. Therefore the color change due to iridophores will be slower than that caused by chromatophores. Leucophores are yet another type of cells active in cuttlefish camouflage, producing white spots by scattering and reflecting incoming light in order to evoke disruptive coloration in cuttlefish. “Often these cells are used in combination. For example, in camouflage, the chromatophores will be used to match the background color, iridophores will reflect light, to disguise visible organs, and leucophores may be used to break up the body pattern.” (Wood and Jackson, 2004, p6). According to biologist Roger Hanlon (2007), all the patterns fit into three basic types: uniform, mottled, and disruptive. The cuttlefish can even change the texture of its skin from rock smooth to bumpy to spiky. These transformations are made possible by special cells in their skin called papillae. Since cuttlefish live in complex environments such as coral reefs and mangrove swamps having a wide variety of colors and textures their quick-change abilities are constantly tested. References Animal Guide: Cuttlefish. Accessed 11 April 2009 Chaddha, R. 2007. Anatomy of a Cuttlefish. Accessed 13 April 2009 Hanlon R (2007) Cephalopod dynamic camouflage. Current Biology 17(11): R400-404 Review by Myers, P.Z. 6 June 2007 Accessed 12 April 2009 Lewis, S.K. 2007. Quick change artists. Accessed 12 April 2009 Messenger, J.B. “Cephalopod chromatophores: neurobiology and natural history”. Biology Reviews Cambridge Philosophic Society. 76.4 (2001): 473-528 Wood, J and Jackson, K. 2004. “Introduction to: Why cephalopods change color” Accessed 11 April 2009 Read More