Evolution of calcification in extant coccolithophores
We have recently identified a unique morphological characteristic in the Isochrysidale coccolithophore Emiliania huxleyi [13]: E. huxleyi cells appear to be surrounded by a cell wall analogous structure. Such a morphology is unique among haptophyte species described to date and will have implications for differing mechanisms of substrate transport supporting coccolithogenesis. Our results support the earlier findings of Van der Wal et al. (1985) that proposed a multi-layer cell cover in E. huxleyi. Were this morphology limited to certain orders of haptophytes, it could be used as a defining trait to help resolve haptophyte phylogeny. Specifically, it could be used to clarify the divergence of the Isochrysidales and Syracosphaerales+Zygodiscales after their divergence from the Prymnesiales. Definitive characterisation of the cell wall analogous structure in E. huxleyi is necessary to understand its significance for the cellular biology of the species. In addition, detailed comparative morphological analysis of other coccolithophores is necessary to place these findings in an evolutionary context.
