Ithycythara pentagonalis is a species of sea snail, a marine gastropod mollusc in the family Mangeliidae.
Tucker considers Ithycythara auberiana a synonym of Ithycythara pentagonalis <small>Reeve, L.A., 1845</small>
The smooth, ivory white shell has an oblong-ovate shape. It is longitudinally five-angled. It shows compressed ribs at the angles, pointed at the upper part of the ribs.
This marine species occurs off St Vincent, West Indies.