Sellaphora stroemii, S. ventraloides and S. aggerica are similar in size, shape, stria density, and the presence of grooves that are visible in LM. For all of these taxa, valves at the small end of the size range are so similar that they may not be distinguishable from one another. The stria density is slightly lower and valve ends are often subcapitate in S. stroemii and S. ventraloides. The valves of S. aggerica are more narrow.