RICH STRUCTURE. “These additional quarks and antiquarks are referred to as sea quarks. Collectively quarks and gluons are referred to as partons. It is not possible to identify any individual up or down quark as a sea or valence quark, but antiquarks and strange quarks must belong to the sea, so their study promises to reveal information about the structure of the proton.”
https://www.nature.com/articles/s41586-021-03282-z