Pinnularia parvulissima should be compared to P. gibba and P. subgibba. Pinnularia gibba is larger in size and has more capitate ends than P. parvulissima. Pinnularia parvulissima is smaller in size and has a smaller length to width ratio than P. subgibba (4.5-6.5 vs. 7-8). Pinnularia parvulissima also has a broader fascia and more convex sides than P. subgibba.