Photophores are light emitting cells that range from simple clusters to more complex organs surrounded by reflectors, lenses, light guides, color filters and muscles. Young and his collaborators have prepared an excellent diagram and glossary of these structures here.
Photophores can be found nearly anywhere on the body of a squid. The most commonly classified ones are: ocular photophores; abundant mantle (head and arms also); visceral photophores, funnel photophores; tentacular photophores.
In a number of deep sea animals sexual dimorphism of photophores exists, although the use and recognition of signalling between the sexes is not yet understood (Jones 2000).
is a species of squid that has the largest photophores in the animal kingdom. These organs can be up to 5 cm in length and are found in the tips of the tentacle arms. T. danae
will flash their photophores rapidly when threatened to confuse their attacker. It is questionable still whether this behavior actually deters predators (Bolstad 2003).
Photophore morphology has been well documented by Herring et al. Their study described the ventral mantle of a single Abralia veranyi
specimen to bear more than 550 photophores. The study described the arrangement in precise detail: " Large photophores were arranged in transverse rows of 4 to 6 interspersed with much more numerous smaller ones. Large photophores were either refractive or non-refractive, while the smaller were either simple and opaque or complex and clear. Simple small photophores and nonrefractive large ones were never illuminated during the study."
Figure (above): Sepioteuthis sepioidea chromatophores and photophores. Photographed by Roger Hanlon.
Figure (left): juvenile Taningia danae. Photographed by Richard Young.