A view of the frustule from the top (or bottom), such that the valve face or interior of the valve is visible, but typically not the girdle. One of two common views of diatom frustules in microscopy (contrasted with girdle view).
References
Hasle, G.R. & Syvertsen, E.E., 1996. Marine Diatoms. In C.R. Tomas (ed), Identifying Marine Diatoms and Dinoflagellates. Academic Press, Inc., California. pp. 5-385.
