Genetic differentiation within the Paralia longispina (Bacillariophyta) species complex

We report on undiscovered genetic and morphological diversity within a diatom taxon known as Paralia longispina and propose three new, extant species of Paralia - Paralia allisonii sp. nov., Paralia crawfordii sp. nov., and Paralia ehrmanii sp. nov. - obtained from subtropical and tropical coasts of the Atlantic and Pacific oceans. Comprehensive examination and hierarchical clustering of frustule characters separated these three species from each other and from P. longispina. Each species possessed one or two unique morphological diagnostic characters. The internal transcribed spacer (ITS) region and a fragment of the small subunit (18S rRNA gene) of nuclear encoded rRNA and a portion of the 5' end of the large subunit of the ribulose bisophosphate carboxylase (rbcL) gene of the chloroplast genome were related to the morphological groupings of monoclonal isolates of P. allisonii and P. crawfordii. The ITS2 secondary structure of the cultured clones of these two species had four helices. They differed by five hemicompensatory base changes (HCBCs) and substantial changes to the distal end of helix I, the region between helix II and helix III, and nearly all of helix IV. Our results better our understanding of the distribution of subtropical and tropical species of Paralia and have practical implications for the conservation of native microbial florae and for the possibility of ship ballast in human-mediated dispersal of these diatoms.