In prorocentroids (desmokonts), large apical pores found in the periflagellar area: auxiliary pore (A) and/or the flagellar pore (F). A periflagellar collar can surround these pores; e.g. P. maculosum and P. formosum.
Prorocentrum formosum: only one periflagellar pore present, the flagellar pore. F=flagellar pore.
Prorocentrum maculosum: periflagellar pores. A periflagellar collar surrounds these pores. A=auxiliary pore; F=flagellar pore.