Diloma nanum is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.
The small, solid, brown shell has an oval-round shape with a diameter of 5 mm. It contains four convex, very distinct whorls. The apex is simple. The light-colored base of the shell is rounded and hardly perforated. The umbilicus is rather large and plicate-crenulate. The arcuate columella is denticulate. The inner lip is undulate. The throat is livid.
This marine species occurs off the Ryukyu Islands
