Can you combine chromatophores with exoskeleton

Question

I've got an idea of an alien organism that is a powerful predator that shares its environment with extremely intelligent, strong, and dangerous apex predators, and so it evolved an exoskeleton. Its prey evolved to run extremely fast for long distances so it had to evolve to be an ambush predator. Since it lives on a planet that is very bright and has intelligent prey it had to evolve a more complex form of stealth, chromatophores.

Is there a way to combine chromatophores with the exoskeleton?

Answer 1

Welcome to WBSE!

So to start off, defensive structures in earth animals are all somewhat inorganic, or more specifically mineral-based. Shells, exoskeletons and mammalian or reptilian scales all share a common trait of having no living cells in the protective layer, usually growing from a ‘root’. Since chromatophores are cells, this poses a limiting factor in that the two structures are exclusive. If your question is ‘can insect-like exoskeletons have chromatophores?’ then no. If instead you want to know if they can coincide, then possibly.

So the first and simplest answer I have is transparency. A transparent exoskeleton with chromatophores underneath would serve the proposed purpose, but it’s important to keep in mind that this only really works with thin layers of exoskeleton, as light would find it harder to reach the colour changing skin through thicker layers. This thin armour is less of a problem for small animals, but since you haven’t specified size and describe them as ‘powerful’ I’ll assume they aren’t small.

My second suggestion would be osteoderms (literally ‘bone-skin’, like ankylosaurs or other reptiles) covered in skin - similar to the sheaths of a lion fish’s barbs. The individual osteoderms would have to be small to allow efficient blood flow to the skin covering, and to minimise tearing, but the anatomy would be somewhat like laying a t-shirt over chainmail in armour terms.

Finally, if you’re really stuck on exoskeleton and not bone plates or similar, then nature has an example. The Panamanian golden tortoise beetle has a number of layers within its shell that reflect light to form their gold colour, and below that is a stationary red pigment. The beetles control fluid within grooves on these layers to control the visibility of the tiers, and therefore their colour. When the grooves a filled, the layers are complete and reflect gold. When the grooves are empty, light passes through the layers like a shutter and only the red pigment is visible. This is simple but very similar to chromatophores, so it isn’t too unreal to scale it up. Again though, this is a mostly transparent exoskeleton, so thickness may be limited (though maybe less so than option 1?). Exoskeleton would likely need to form scales or plates to ensure proper control over fluid at any point on the armour.

All of this is based on Earth biology however, and so an alien with differently designed cells and adaptions may have more tools to work around these limitations. Also keep in mind that larger animals usually don’t have armour in the form of hard plating on earth, resorting to size and or tough/thick skin/fat for protection. looK up male boar shoulder shields - there are other options for protection.

Answer 2

The chromatophores could be a symbiotic epiphyte -- like moss -- and grow on the beast's exoskeleton, reacting to both its background and chemical messaging -- similar to ants -- generated by the host.

The epiphyte benefits from the body warmth of the beast and maybe the detritus of dead cells sloughing off, and the host gains camouflage.

To promote this relationship, the exoskeleton could have pores that feed nutrients and water and maybe fungicides that suppress other flora from growing on its surface.

The growth would start when the beast was born or hatched, the infestation transferred from the parents.

Or, it could be like spindle worms, that burrow into the exoskeleton and spread across the surface -- so more of a parasite than a true symbiote.