Japanese Hiragana P's?

Question:

Ok so i get all the other series but the P's (pa', 'pi', 'pu', 'pe', 'po') why in Hiragana do they have circles above them http://japanese-lesson.com/characters/hiragana/index.html if you look at the P row why do they have circles above them?

Answer:

That is what designates that the sound is changed to the P sound.
Without any marking, the pronunciation is the H series (ha/hi/fu/heho)
With the " marking, the pronunciation is the B series (ba/bi/bu/be/bo)

They just couldn't think of 10 more original characters to use that would look appropriate and yet be royalty-free. (They're so fussy about things like that)