It is one alga, several algae.
algae
The plural of alga is algae.
The plural of alga is algae. The plural possessive is algae's.
ALGAE is the plural form, commonly used in place of the singular ALGA because references to a single organism are rare.
The word 'algal' is an adjective, a word that describes a noun as of or relating to alga. Adjectives do not have a plural form.
The plural for algae is actually just algae
The plural form of apparatus is apparatuses. It has no foreign plural.
Forum---Plural Form Forums,Foreign Plural Form Forumina
The foreign plural of addendum is "addenda."
The foreign plural of "prospectus" is "prospectuses."
Well, the English Plural is momentums and the Foreign Plural is momenta!
Stimuli is already the plural of stimulus.
The foreign plural of agendum is agenda.