The eyespotted (female)Halimeda tunagamete has been studied under the electron microscope. It has an uncondensed nucleus showing a ribosome-studded envelope and inner (chromatin) aggregations, a rough endoplasmic reticulum and a rather large amount of free ribosomes. The single plastid is provided with a large thylakoidal outfit, 4–6 starch grains and rows of concentrically arranged double membranes. From 4 to 6 mitochondria are present. The Golgi apparatus consists of 2–3 stacks of a few poorly developed saccules and a large population of vesicles very rich in polysaccharide contents.