Pigment granule architecture varies across yellow, red, and brown chromatophores in squid Doryteuthis pealeii.

Cephalopods produce dynamic colors and skin patterns for communication and camouflage via stratified networks of neuronally actuated yellow, red, and brown chromatophore organs, each filled with thousands of pigment granules. While compositional analysis of chromatophore granules in Doryteuthis pealeii reveals the pigments as ommochromes, the ultrastructural features of the granules and their effects on bulk coloration have not been explored. To investigate this, we isolated granules from specific colored chromatophores and imaged them using multiple modalities.

Networks of linked radial muscles could influence dynamic skin patterning of squid chromatophores.

The visibility of cephalopod chromatophore organs is regulated dynamically by rosettes of obliquely striated radial muscles that dilate or relax the diameter of a central pigmented sacculus in 100-300 ms. Each of the several dozen muscles has a flared proximal end that adheres tightly to its pigmented sacculus and an extremely elongated distal end which branches into single fibrils that anchor into the dermis. This geometry provides ample opportunity for overlap of the many muscles from neighboring chromatophores.

Dynamic pigmentary and structural coloration within cephalopod chromatophore organs.

Chromatophore organs in cephalopod skin are known to produce ultra-fast changes in appearance for camouflage and communication. Light-scattering pigment granules within chromatocytes have been presumed to be the sole source of coloration in these complex organs. We report the discovery of structural coloration emanating in precise register with expanded pigmented chromatocytes.

Retinal specializations and visual ecology in an animal with an extremely elaborate pupil shape: the little skate Leucoraja (Raja) erinacea Mitchell, 1825.

Investigating retinal specializations offers insights into eye functionality. Using retinal wholemount techniques, we investigated the distribution of retinal ganglion cells in the Little skate Leucoraja erinacea by (a) dye-backfilling into the optic nerve prior to retinal wholemounting; (b) Nissl-staining of retinal wholemounts. Retinas were examined for regional specializations (higher numbers) of ganglion cells that would indicate higher visual acuity in those areas.

White reflection from cuttlefish skin leucophores.

The highly diverse and changeable body patterns of cephalopods require the production of whiteness of varying degrees of brightness for their large repertoire of communication and camouflage behaviors. Leucophores are structural reflectors that produce whiteness in cephalopods; they are dermal aggregates of numerous leucocytes containing spherical leucosomes ranging in diameter from 200-2000 nm. In Sepia officinalis leucophores, leucocytes always occur in various combinations with iridocytes, cells containing plates that function as Bragg stacks to reflect light of particular wavelengths.

The structure-function relationships of a natural nanoscale photonic device in cuttlefish chromatophores.

Cuttlefish, Sepia officinalis, possess neurally controlled, pigmented chromatophore organs that allow rapid changes in skin patterning and coloration in response to visual cues. This process of adaptive coloration is enabled by the 500% change in chromatophore surface area during actuation. We report two adaptations that help to explain how colour intensity is maintained in a fully expanded chromatophore when the pigment granules are distributed maximally: (i) pigment layers as thin as three granules that maintain optical effectiveness and (ii) the presence of high-refractive-index proteins-reflectin and crystallin-in granules.