Endosymbiosis and the Origin of Eukaryotic Algae with a focus on Glaucophytes, Chlorarachniophytes, and Apicomplexans

Eukaryotes are all chimeric organisms, containing genomes and genes derived
from more than one original organism by endosymbiosis, but algae are the world's
champions, with various groups having originated by primary, secondary and
tertiary endosymbioses, containing genes from multiple sources. This chapter
details the fossil history of eukaryotic algae, the various types of organisms
that can occur in algal cells, and occurrences of algae in the cells of other
organisms. Glaucophytes are presented as examples of origin by primary
endosymbiosis, chlorarachniophytes as examples of a group that originated by
secondary endosymbiosis, and dinoflagellates as exemplars of tertiary
endosymbiosis and horizontal gene transfer. Of particular interest to
evolutionary biologists, the unresolved issues noted in this chapter could
form the basis for lively classroom debate.