A topographic feature of the periflagellar area of some prorocentroids (desmokonts); platelets situated around the periflagellar pores. They are thin, flat, and sometimes curved thecal extensions of an apical plate. They can be large and visible via LM (e.g. Prorocentrum emarginatum and P. sculptile), or much smaller and only visible via SEM (e.g. P. formosum).
Prorocentrum emarginatum: anterior view of periflagellar area. Large angled rectangular apical plate.
Prorocentrum formosum: small periflagellar plate (arrowhead) adjacent to flagellar pore (F).
Prorocentrum sculptile: large curved thin inclined apical plate (small arrows).