Zooplankton - The animals of the plankton as opposed to the plants (phytoplankton).

Zygomatic Arch - The cheekbone of a mammal. Formed by the union of the jugal bone at the from and part of the squamosal at the back.

Zygote - The diploid cell formed as the union of two haploid sex cells or gametes. The zygote is the first cell of a new generation and gives rise by division to all the cells of the new individual.