There are no septae, and the many discoid chloroplasts, nuclei and other organelles are free to move through the organism.

In the genus Halimeda, whole seabed meadows may consist of an individual, single-celled organism connected by filamentous threads running through the substrate.

Under certain conditions, sexual reproduction occurs in a process called holocarpy.

Almost all of the cytoplasm in the thallus is converted into biflagellate gametes, which are discharged into the sea through papillae.

After fertilisation, the zygote becomes a protonema and this, in turn, develops into a new thallus.