New marine members of the genus Hemiselmis (Cryptomonadales, Cryptophyceae)

Cryptomonads are a ubiquitous and diverse assemblage of aquatic flagellates. The relatively obscure genus Hemiselmis includes some of the smallest of these cells. This genus contained only two species until 1967, when Butcher described seven new marine species mainly on the basis of observations with the light microscope. However, from these seven taxa, only H. amylifera and H. oculata were validly published. Additionally, the features Butcher used to distinguish species have since been questioned, and the taxonomy within Hemiselmis has remained clouded due to the difficulty in unambiguously applying his classification and validating many of his species. As a result, marine strains are often placed into one of three species - H. rufescens Parke, H. virescens Droop, or the invalid H. brunnescens Butcher - based on cell color alone. Here we applied microscopic and molecular tools to 13 publicly available Hemiselmis strains in an effort to clarify species boundaries. SEM failed to provide sufficient morphological variation to distinguish species of Hemiselmis, and results from LM did not correlate with clades found using both molecular phylogenetic and nucleomorph genome karyotype analysis, indicating a high degree of morphological plasticity within species. On the basis of molecular characters and collection geography we recognize four new marine species of Hemiselmis - H. cryptochromatica sp. nov., H. andersenii sp. nov., H. pacifica sp. nov., and H. tepida sp. nov. - from the waters around North America.