Internal view of initial and post-auxospore valves as observed in SEM.

A & B—note absence of rimoportula; C & D—rimoportulae near the valve mantle edge aligned perpendicularly to the mantle rim (arrowheads); E & F—hammock-shaped rimoportulae (arrowheads) with internal openings variably oriented with respect to the mantle rim; G & H—low-profile rimoportulae in typical position for a vegetative valve (arrowheads), underneath the mantle rim and parallel to rim’s circumference (focus is on the distal rim). Note imperfect striation and external ornamentation of the mantle on some of the valves.