This is a tricky question because it depends on what we are comparing. Here's why:

* Clay: Clay particles are incredibly small, on the order of nanometers to micrometers. Their thickness is not something we typically measure.

* Planktonic Microskeletons: Planktonic organisms (like diatoms, foraminifera, and radiolarians) have skeletons made of different materials (silica, calcium carbonate, etc.). The thickness of these skeletons varies wildly depending on the species.

So, to answer your question, we need more information:

* What specific clay are we comparing?

* What specific planktonic microskeletons are we comparing?

Generalizations:

* Clay is usually much thinner than most planktonic microskeletons. This is because the clay particles themselves are very small, while planktonic microskeletons are structures built by organisms.

* Within planktonic microskeletons, there is a wide range of thickness. Some species have very thin skeletons, while others have very thick skeletons.

If you can provide more specific details about the clay and the planktonic organisms, I can give you a more precise answer.