Definitions

Little eye, distinct from main organ of vision. [Williams, 1984]
Simnple single eye or eye spot; common in some branchiopods and copepods.
See: Naupliar eye [McLaughlin, 1980]
Unpaired median eye, common in some branchiopods (e.g., Notostraca) and copepods (e.g., Cyclopoida) but otherwise uncommon. [Moore and McCormick, 1969]
(Taxon-specific: Order Cladocera) Nauplius eye. [Stachowitsch, 1992]
(Taxon-specific: Subclass Branchiura) Nauplius eye. [Stachowitsch, 1992]
(Taxon-specific: Subclass Mystacocarida) One of four photosensitive organs located dorsally on anterior (annteulary) part of cephalon (head). (with/without lens). [Stachowitsch, 1992]
(Taxon-specific: Class Ostracoda) One of three simple photosensitive structures forming nauplius eye. (closely adjoining, widely separated). [Stachowitsch, 1992]