Molecular and Morphological Investigations of the Stauros-bearing, Raphid Pennate Diatoms (Bacillariophyceae): Craspedostauros E.J. Cox, and Staurotropis T.B.B. Paddock, and their Relationship to the Rest of the Mastogloiales.

Several lineages of raphe-bearing diatoms possess a "stauros," which is a transverse, usually thickened area free of pores across the center of the valve. It has been suggested that this structure has evolved several times across the raphid diatoms, but we have noticed similarities beyond the stauros between two marine genera-Craspedostauros and Staurotropis-in the structure of their pore occlusions. We have isolated, cultured and extracted DNA from several strains of both genera to infer the phylogenetic relationship between these taxa, as well as test the suggested relationship of Craspedostauros to Achnanthes and Mastogloia based on plastid morphology.

Conserved gene order and expanded inverted repeats characterize plastid genomes of Thalassiosirales.

Diatoms are mostly photosynthetic eukaryotes within the heterokont lineage. Variable plastid genome sizes and extensive genome rearrangements have been observed across the diatom phylogeny, but little is known about plastid genome evolution within order- or family-level clades. The Thalassiosirales is one of the more comprehensively studied orders in terms of both genetics and morphology.