Coralline life cycle

Plasmogamy: Fusion
of the cytoplasm without
nuclear fusion
(karyogamy).

Karyogamy: Fusion of the
nuclei of two gametes after
cytoplasmic fusion
(plasmogamy).

Zygote: the diploid product of the fusion of two haploid gametes. In corallines, as in most red algae, there is no real zygote per se. In red algae, the diploid nucleus (or zygote nucleus) may move cells before it develops rapidly into the carposporophyte.

Tetrasporophyte: diploid, free-living stage in the life cycle of coralline and other red algae in which meiosis takes place. Tetrsporophytes bear either tetrasporangial conceptacles (Corallinaceae) or tetraporangial sori (Sporolithaceae).

The carposporophyte develops from the zygote nucleus following fertilization. It is thus diploid. It remains within the female conceptacle, which enlarges to accomodate it. In the diagram, the carposporophyte is seen to consist of the gonimoblast filaments (g), each of which terminates in a carposporangium (c) which produces a single carpospore. In this case, the gonimoblast filaments arise from the periphery of a single discoid fusion cell (arrow). The filaments making up the walls and roof of the conceptacle are haploid filaments of the gametophyte. The conceptacle and its contents are sometimes referred to as a cystocarpic conceptacle, although strictly speaking it is still a female conceptacle.

Titanoderma pustulatum (UWC: 93/176)

Diploid: having twice the haploid chromosome number. Following fertilization, a diploid carposporophyte develops within the female conceptacle. The diploid carposporophyte produces diploid carpospores by mitosis, and these are released and grow into diploid tetrasporophytes.

Haploid: having half the diploid chromosome number. In coralline algae meiosis takes place in the tetrasporophyte to gice rise to haploid tetraspores. The haploid tetraspores grow into haploid gametophytes. The tetraspores and the gametophytes are the only haploid stages in the coralline algae.