Final answer:
Islets are small pieces of land surrounded by water that may fill in gaps between continents, providing clues for the reconstruction of ancient supercontinents.
Step-by-step explanation:
Small pieces of land surrounded entirely by water that are now eroded away, but would likely fill in the gaps where continents don't match up exactly are best described as islets. An islet is a small island and could be thought of as pieces that were once part of a larger landmass and have separated due to erosion or other geological processes. The presence of islets might provide clues for matching continental shapes, similar to fitting pieces of a puzzle together when trying to reconstruct ancient supercontinents like Pangea.