Mastogloiopsis biseriata, gen. et sp. nov., a diatom without partecta, is very similar to the Marginulatae group of Mastogloia
Lobban, Christopher S.; Navarro, J. Nelson
Stalked cells with mastogloioid plastids were discovered in Guam, Puerto Rico and Easter Island. Living cells and acid-cleaned frustules in the light microscope resemble Mastogloia Thwaites ex Wm. Smith group Marginulatae Simonsen [M. ciskeiensis Giffen, M. cuneata (Meister) Simonsen, M. inaequalis Cleve], but lack partecta. Scanning electron microscopy revealed biseriate striae comprising simple areolae - in contrast to the pseudoloculate structure in Mastogloia species - and a narrow, porate flange on the pars interior of the valvocopula instead of a partectal ring. The pores suggest that there is a space within the flange, i.e., it is not merely a septum, but it is not clear whether the interior space is canal-like or slit-like. The pars interior also has a groove that interlocks with the valve. Mastogloiopsis biseriata gen. et sp. nov. is placed in the Order Mastogloiales, to which Mastoneis biformis also probably belongs.