The ultrastructure of the integument of the sapphirinid copepods was studied by scanning and transmission electron microscopy. Samples were collected between 1991 and 1993 by plankton-net tows from the subtropical and tropical waters of the North Pacific. In all the seven species examined of Sapphirina and Copilia, a structure with multilayered platelets was found in the epidermal cells of the dorsal integument of the male. Each platelet is a regular hexagonal prism. The platelets form a plate with honeycomb arrangement within each epidermal cell. Just ventral to the dorsal cuticle, 10 to 14 plates are located parallel to each other and to the cuticle. The mean diameter and thickness of the platelets measured between 1.0 and 1.8 mu m and 61 and 83 nm, respectively, for the four species. The specific coloration of seven species was examined with reflected and transmitted light. The iridescent color may be explained by the theory of multiple thin-layer interference in some species which are considered to have an ideal laminar structure, but for the other species, mechanisms from non-ideal systems, including pigment-thin layer interaction, may also be involved.
