What feature was not present in the first eukaryotes?

Cell walls. Or even mitochondrion

Explanation:

Eukaryotes at first did not have cell walls. They also didn't have mitochondrion. But the answer is probably cell wall.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.