Editing Camouflage (section)

=== Transparency ===

{{further|Underwater camouflage}}

[[File:Expl0469 - Flickr - NOAA Photo Library.jpg|thumb|upright|left|Many animals of the open sea, like this ''[[Aurelia labiata]]'' jellyfish, are largely transparent.]]

Many [[Sea|marine]] animals that float near the surface are highly [[Transparency and translucency|transparent]], giving them almost perfect camouflage.{{sfn|Herring|2002|pages=190–191}} However, transparency is difficult for bodies made of materials that have different [[refractive index|refractive indices]] from seawater. Some marine animals such as [[jellyfish]] have gelatinous bodies, composed mainly of water; their thick [[Mesoglea|mesogloea]] is acellular and highly transparent. This conveniently makes them [[buoyancy|buoyant]], but it also makes them large for their muscle mass, so they cannot swim fast, making this form of camouflage a costly trade-off with mobility.{{sfn|Herring|2002|pages=190–191}} Gelatinous [[plankton]]ic animals are between 50 and 90 percent transparent. A transparency of 50 percent is enough to make an animal invisible to a predator such as [[cod]] at a depth of {{convert|650|m|ft}}; better transparency is required for invisibility in shallower water, where the light is brighter and predators can see better. For example, a cod can see prey that are 98 percent transparent in optimal lighting in shallow water. Therefore, sufficient transparency for camouflage is more easily achieved in deeper waters.{{sfn|Herring|2002|pages=190–191}}

[[File:Hyalinobatrachium uranoscopum01a.jpg|thumb|upright|[[Glass frogs]] like ''[[Hyalinobatrachium uranoscopum]]'' use partial transparency for camouflage in the dim light of the rainforest.]]

Some tissues such as [[muscle]]s can be made transparent, provided either they are very thin or organised as regular layers or fibrils that are small compared to the wavelength of visible light. A familiar example is the transparency of the lens of the vertebrate [[eye]], which is made of the protein [[crystallin]], and the vertebrate [[cornea]] which is made of the protein [[collagen]].{{sfn|Herring|2002|pages=190–191}} Other structures cannot be made transparent, notably the [[retina]]s or equivalent light-absorbing structures of eyes – they must absorb light to be able to function. The [[camera]]-type eye of vertebrates and cephalopods must be completely opaque.{{sfn|Herring|2002|pages=190–191}} Finally, some structures are visible for a reason, such as to lure prey. For example, the [[nematocyst]]s (stinging cells) of the transparent [[siphonophore]] ''[[Agalma okenii]]'' resemble small [[copepod]]s.{{sfn|Herring|2002|pages=190–191}} Examples of transparent marine animals include a wide variety of [[larva]]e, including [[radiata]] (coelenterates), siphonophores, [[salps]] (floating [[tunicate]]s), [[gastropoda|gastropod molluscs]], [[polychaete]] worms, many shrimplike [[crustacean]]s, and fish; whereas the adults of most of these are opaque and pigmented, resembling the seabed or shores where they live.{{sfn|Herring|2002|pages=190–191}}{{sfn|Cott|1940|page=6}} Adult [[comb jelly|comb jellies]] and jellyfish obey the rule, often being mainly transparent. Cott suggests this follows the more general rule that animals resemble their background: in a transparent medium like seawater, that means being transparent.{{sfn|Cott|1940|page=6}} The small [[Amazon River]] fish ''[[Microphilypnus amazonicus]]'' and the shrimps it associates with, ''[[Pseudopalaemon gouldingi]]'', are so transparent as to be "almost invisible"; further, these species appear to select whether to be transparent or more conventionally mottled (disruptively patterned) according to the local background in the environment.<ref>{{cite journal |title=The almost invisible league: crypsis and association between minute fishes and shrimps as a possible defence against visually hunting predators |author1=Carvalho, Lucélia Nobre |author2=Zuanon, Jansen |author3=Sazima, Ivan |journal=Neotropical Ichthyology |date=April–June 2006 |volume=4 |issue=2 |pages=219–224 |doi=10.1590/S1679-62252006000200008|doi-access=free }}</ref>