ABSTRACT
Introduction ....................................................................................................................................171 General features of the chlorarachniophytes .................................................................................172 The nucleomorph ...........................................................................................................................175 Secondary endosymbiosis generated the chlorarachniophytes .....................................................175 How the green algal endosymbiont was integrated as a plastid ...................................................176 Life cycle diversity.........................................................................................................................176 Behaviour of daughter cells ...........................................................................................................177 Classification of the chlorarachniophytes......................................................................................178 Phylogeny of chlorarachniopytes...................................................................................................180 Acknowledgments ..........................................................................................................................181 References ......................................................................................................................................181
The chlorarachniophytes are one of the most evolutionarily interesting algal groups. Their cells have small organelles, called nucleomorphs, which provide us with direct evidence for the lateral transfer of plastids through a secondary endosymbiosis. Advances in molecular phylogenetics have proved that the chlorarachniophytes originated from a cercozoan protist that engulfed a green alga and retained it as a plastid. The focus of chlorarachniophyte research has now shifted to tackling the question “how did the endosymbiont become an organelle?” In addition to this evolutionary research, the recognition of the chlorarachniophytes as a group and their diversity has also progressed in the past decade. Currently, five genera and nine species make up the chlorarachniophytes and several new taxa are waiting to be described. Remarkable diversity in life cycle and ultrastructure and fascinating cell behaviour are beginning to be revealed.
