I was searching online for quite a while this evening, chasing a half-remembered bit of trivia, that trilobites were supposedly unique in their use of calcite for their lenses, composing the ommatidia of their compound eyes.

It must be so obvious to scientists in the field of studying insects that they never mention it in their papers…

So, what compound(s) do modern arthropods use in their compound eyes. If it isn’t calcite, what do modern ‘bugs’ use?