the first larval stage in the development of certain crustaceans, typically unsegmented with only three pairs of appendages, all on the head, and an unpaired median eye
See nauplius in American Heritage Dictionary 4
(nôˈplē-əs)
nounpl.nau·pli·i(-plē-īˌ)
The free-swimming first stage of the larva of certain crustaceans, having an unsegmented body with three pairs of appendages and a single median eye.