Democritus didn't have any specific idea about what atoms looked like. He wasn't able to see atoms, and his ideas were based on philosophical reasoning, not scientific observation.

Here's what we know about Democritus's atomic theory:

* Atoms are solid and indivisible. He believed that matter couldn't be infinitely divided, and there was a point where you'd reach the smallest, fundamental particle: the atom.

* Atoms are constantly in motion. He thought that atoms were always moving and colliding, creating the diversity of matter we see.

* Different atoms have different sizes and shapes. This was his explanation for the variety of substances in the world.

He didn't assign any specific shapes or structures to atoms, and we don't know if he thought they had any internal structure at all.

It's important to remember that Democritus lived in ancient Greece, and his ideas were purely theoretical. It took centuries for scientists to develop the tools and methods to actually observe and investigate atoms.