Correlation of iridescence with changes in iridophore platelet ultrastructure in the squid Lolliguncula brevis

Cephalopods are renowned for their unique colour change system in which neurally controlled chromatophore organs in the dermis work in combination with subjacent iridescent cells (iridophores) to produce colours and patterns of a wide range (Messenger, 1979; Hanlon, 1982). Some iridophores in squids are physiologically active and reversibly change from non-iridescent to iridescent (Hanlon,1982) We discovered examples of these active iridophores in the dorsal mantle of the squidLolliguncula brevis. The state of iridescence in these dorsal mantle iridophores can be controlled in vitro in isolated dermal layers with the putative neuromodulator acetylcholine (ACh), as well as by means of other factors (Hanlon & Cooper, 1985). We compared the ultrastructure of non-iridescent and iridescent iridophores in these isolated dermal layers to determine the cytological basis for the change in optical properties. In this paper we report the correlation of structural changes within the iridophore platelets with the appearance of iridescence.