Ctenophores swim using eight rows of comb plates, each plate a block of thousands of cilia fused at their bases. The plates beat in metachronal waves running along the body, the largest ciliary propulsion system in the animal kingdom. Ctenophores are the largest animals known to swim primarily by cilia rather than muscle.
The rainbow effect is diffraction. Ordered ranks of cilia act like a grating, splitting incident light into travelling bands of colour that appear to run down the animal. Photograph one under a lamp and the colours appear; switch the lamp off and they vanish, because there is no light being emitted.
Separately, many ctenophores including Mnemiopsis leidyi are genuinely bioluminescent, producing a dim blue-green glow from photoproteins in the canals beneath the comb rows. Mnemiopsis is also notable for what it lacks: comb jellies have no stinging cells. Most capture prey with colloblasts, adhesive cells that stick to it, though the lobed forms such as Mnemiopsis rely heavily on their muscular lobes and ciliated grooves to engulf plankton.