Coleoid cephalopods could display background color (and texture) information at a chromatic and spatial resolution in excess of predator visual acuity. For example, cephalopod camouflage might really be sophisticated color disruption. Mimicry might not be the right term for this phenomenon. While it is certainly impressive that cephalopods can mimic color incredibly well despite being colorblind in their eyes and being capable of mimicking color when the eyes are removed (Sereni, 1930), perhaps knowing the color of the background is not necessary. The most mysterious quality about cephalopod crypsis is that cephalopods are believed to be colorblind (Sereni, 1930). several seconds to minutes) and thus may be controlled by neurohormones, a diffusible cue, or weak electric coupling to an unidentified intermediary. Unlike chromatophores, it remains dubious that iridophores are controlled directly by neural inputs because they respond much more slowly (ca. By combining reflection from the iridophores with the correct patterning of chromatophores, the cephalopod can create a very convincing copy of the surrounding conditions. When observed from above, iridophores can appear blue, but when observed at a more oblique angle, they appear to reflect red light. Interestingly, the color an iridophore reflects is dependent on the angle from which they are observed (Mathger & Hanlon, 2007). Iridophores are stacks of very thin cells that are capable of reflecting light back at different wavelengths (Cloney & Brocco, 1983) and possibly different polarities (Mathger & Hanlon, 2007). Other colors are attainable by using a second layer of structures in the cephalopod skin called iridophores (Cooper & Hanlon, 1986). However, these three colors are particularly useful at the depths wherein many camouflaging cephalopods live (Bush et al., 2009). Yet there are certainly other colors that need to be mimicked but which cannot be made by combining "pixels" of just those three. The chromatophores can be opened quickly because they are controlled neurally: squid, cuttlefish and octopuses can change colors within milliseconds (Hanlon, 2007).Ĭamouflage using chromatophores is particularly impressive because chromatophore pigments are typically only red, yellow, or brown (Hanlon et al., 2011). 2, C), is thought to be responsible for contracting the chromatophore after it has opened (Florey, 1969). The elastomeric properties of the membrane around the pigment granules -the cytoeslastic sacculus (Fig. The radial muscles are thought to be connected to each other by gap junctions (Florey, 1969) so that they ‘dilate' the chromatophore in a symmetrical fashion. Early morphologic and physiologic work by Florey (1969) showed that the radial muscles widen the pigment sac with increasing frequency of the nerve electrical activity. 2, D) to pull outward toward the perimeter of the chromatophore, expanding the central pigment sack (Fig. 2, G) causes the radial muscle fibers of the chromatophore (Fig. Electrical activity within a chromatophore nerve (Fig. Many coleoids share these tissues and organs, but the common and mimic octopuses ( Octopus vulgaris and Thaumoctopus mimicus, respectively) have received much attention in popular media over the past decade (Figure 1).Ĭhromatophores are organs that are present in the skin of many cephalopods, such as squids, cuttlefish, and octopuses, which contain pigment sacs that become more visible as small radial muscles pull the sac open making the pigment expand under the skin. In addition to hiding in crevices and small holes that these soft-body mollusks easily fit into (Sheel & Bisson, 2012), many cephalopods rely on sophisticated tissues - the chromatophores, iridophores, leucophores and papillae - to blend in with their surroundings and disrupt their body outlines, making them much more difficult to locate by sight. Survival might be hopeless for soft bodied coleoid cephalopods if it were not for camouflage. Yet based on molecular findings, coleoid cephalopods have been present since the early Devonian period, diverging from their ancestor over 400 million years ago (Bergmann et al., 2006). Coleoid cephalopods, a group that includes octopuses, cuttlefish and squid, experience the selective pressure of predation from eels, nurse sharks, and a great many fishes (Aronson, 1991). The ocean can be a dangerous place, and being a squishy piece of delicious, nutritious muscle is not ideal given that so many capable predators abound.
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