Morphological design and fossil record of the podocopid ostracod naupliar eye

The naupliar eye of podocopid ostracods is a useful character for considering evolution in photic environments. Based on external morphologies and histological observations, naupliar eyes are here categorized into six types. The fossil record demonstrates that the major evolutionary changes in podocopid naupliar eyes occured after the Ordovician. Eye types 1 and 2 are not joined to the carapace by the hypodermal cells, and these two types are found in Palaeozoic ostracods. Eye type 3, 4, 5 and 6 are extended on eye stalks, tightly joined to the carapace by the hypodermal cells, and use the carapace as the refractive cuticle lens. Eye type 3 appeared in the Permian, and eye types 4, 5 and 6 appeared in the Early Jurassic. The design of the podocopid naupliar eye diversified in the Early Jurassic.