Juvenile, adult and reproductive morphologies of Acetabularia acetabulum. This giant alga has a complex life cycle and undergoes distinct developmental phases. From a spherical microscopic zygote, it initiates polarized growth elongating primarily at the tip (or apex) and periodically forming whorls of branched hairs. The reproductive phase starts as the unicell initiates a terminal apical whorl or "cap". When mature, the cap will house gametangia in which gametes form. The thallus and the diploid nucleus are drawn to scale. The number and complexity of the whorls of hairs was reduced for the sake of clarity.