BiomimeticColorChange

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Morphological Colour Change

Chromatophores or pigment cell are color changing cells used most notably by Cephalopods such as squid and octopuses. They are contractile and contain vesicles with stored liquid pigment. To change their color the cells distort their form or size stretching or contracting their outer covering thus changing its translucency or opaquacy. These cells are highly developed and numerous in the cephalopods. wikipedia

The Cephalopoda ("head-foot") or Cephalopods are a class of the phylum Mollusca.

Cephalopods are characterized by bilateral body symmetry, a prominent head, and a modification of the mollusc foot into the form of tentacles. The class contains two subclasses. In the Coleoidea, the mollusc shell has been internalized or is absent; this subclass includes the octopus, squid, and cuttlefish. In the Nautiloidea the shell remains; this subclass includes the nautilus. There are around 650 distinct living species of Cephalopods. An important extinct class is Ammonoidea, the ammonites.

Cephalopods are found in all the oceans of the world and at all depths. They are regarded as the most intelligent of the invertebrates and have well developed senses. They have special skin cells call chromatophores that change color and are used for communication and camouflage.

• http://www.cephbase.utmb.edu/
• http://www.tonmo.com/
• http://tolweb.org/accessory/Cephalopod_Chromatophore?acc_id=2038

"The color patterns of cephalopods are largely controlled by chromatophore organs. A chromatophore organ is composed of a single chromatophore cell and numerous muscle, nerve, glial and sheath cells. Pigment granules lie within the chromatophore cell in an intracellular sac, the cytoelastic sacculus, that has elastic walls. Four to twenty four radially arranged muscle cells, with their associated nerve and glial cells, attach to the cell membrane where the latter is anchored to the cytoelastic sacculus around its equator. The contraction of the muscle cells stretches the lenticular sacculus into a thin, flat disc with serrated edges. The diameter of the sacculus expands up to about 7 times its retracted state which is equivalent to an increase in area of about 50 times. Retraction of the chromatophore apparently results from the elastic nature of the sacculus walls. Primary infoldings and pouches of the chromatophore appear in its upper and lower surfaces during chromatophore retraction and disappear during chromatophore expansion. These foldings are anchored to the sacculus at various points on its surface. The rather structureless sheath cells (not shown in drawing) presumably enable the slippage of the chromatophore organs within the dermis of the skin"

images

Pigment-bearing cells, frequently capable of expansions and contractionswhich change their size, shape and colour.

Octopus, squid, and other cephalopods have developed hiding to a fine art. They can change color in a split second using pigment cells called chromatophores

text below from: http://hermes.mbl.edu/publications/Loligo/squid/skin.0.html

• http://hermes.mbl.edu/

"Many cephalopods have the ability to change their skin color, pattern and even texture rapidly and on demand. The reef squid, Sepioteuthis, can change from a bright red to a greenish hue to almost translucent in the blink of an eye. Other cephalopods have even more impressive displays with moving patterns and shifting iridescence. This ability to control color is another example of the finely-tuned nervous system of cephalopods.

The squid in this example is showing a pattern by selectively ennervating groups of pigmented organs called chromatophores The result is a speckling effect on the mantle and other darker hues on the arms. This is how it appears from a human perspective. Most evidence currently indicates that cephalopods are color blind.

The skin of Sepioteuthis is translucent. There is an underlying layer of white reflecting cells known as leucophores. Color comes from organs full of pigment cells known as chromatophores . These cells are distributed in the dermal (outermost) layer and appear in the photo at left as small patches or dots. Chromatophores contain different types of pigments that result in different colors. Reds, yellows, brown and black are represented by the chromatophores. Other colors such as green and blue seem to be produced by a different group of reflecting cells call iridiphores.

How do Sepioteuthis and other cephalopods control the intensity and variety of colors they show on their skin? Click on the image at left to zoom even closer for a look at the chromatophores.

The chromatophores in the skin of Sepioteuthis appear as colored blobs embedded in a semi-translucent surrounding dermis. They exhibit a variety of colors, shapes and sizes within and amongst species. In this image we can see varying shades of reds, yellows, and black.

The chromatophores are controlled by muscles that are in turn controlled by nerve fibers connected to the brain. The squid can relax or contract these muscles and change the size and shape of the chromatophore. A nerve fiber may have control over several chromatophores. Different colored chromatophores are therefore controlled by different nerves. By controlling the relative sizes of different colors the squid is able to change the hue and intensity of its skin.

This is a model of the chromatophores of Sepioteuthis. Different colored chromatophores are controlled by different nerve fibers. This allows the squid to selectively retract or expand sets of chromatophores and increase or decrease the amount of a selected color. For example, by retracting all of the black pigmented cells, the squid will appear to suddenly lighten. By expanding the red chromatophores, as Loligo may do when excited, the animal will flush with a deep red. The sudden retraction of all the chromatophores (as seen in the illustration) has the net effect of reducing all the colors and the squid appears to fade into the water column.

Think of the pigment cell in the chromatophore, as a flexible bag of color. It can be stretched out to cover a large, flat area or relaxed to shrink back to a small, retracted point. The cell is attached to 30 radial muscle fibers at various points along the edge in a relative plane parallel to the skin surface. These muscles are in turn controlled by a nerve fiber. When a nerve impulse travels to the muscles it causes the muscle fiber to contract. The muscles pull in different directions and expand the cell. Relaxing the muscles allows the cells to return to a smaller and more compact shape, thus reducing the area of the chromatophore and making the pigmented area shrink."

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BiomimeticColorChange Links

• http://lib.fo.am/cgi-bin/view/Libarynth/BioMimicry
• http://www.nature.com/nsu/000914/000914-7.html
• http://biodidac.bio.uottawa.ca/Thumbnails/filedet.htm?File_name=19-3&File_type=GIF
• http://www.biology.lsu.edu/introbio/lab/1208/chemsig.html
• http://www.clarku.edu/departments/biology/biol201/CSantos/Morphological.htm

-- RachelWingfield - 30 Nov 2004
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