Cross-sections of a bristle show a lattice of hollow tubes arranged in a hexagonal pattern with spacing on the scale of light wavelengths. Such a lattice functions as a photonic crystal, reflecting some wavelengths strongly while transmitting others, and the reflected colour shifts with the angle of incidence. Light entering along the axis of the bristle behaves differently again, and the structure has been described as an unusually efficient natural waveguide.
The bristles have a second, blunter function. Long stiff chaetae along the flanks are defensive, and the dense dorsal felt traps sediment, camouflaging an animal that spends most of its time part-buried while it hunts small invertebrates and scavenges.
What the animal gains from the optical effect is genuinely unclear. Much of its habitat is dim, so a bright structural colour may be a by-product of a mechanically useful bristle architecture rather than a signal. The 2001 description of the photonic properties prompted interest in copying the geometry for optical fibres, but structural colour does not, on its own, demonstrate a visual function.