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.
Figure. Cut-away view of a cephalopod chromatophore. Drawing modified from Cloney and Florey, 1968.
