Free-living marine planktonic unarmoured dinoflagellates from the Gulf of Mexico and the Mexican Pacific

Abstract

Abstract The so-called unarmoured dinoflagellates are not a “natural” (phylogenetic) group but they lack thecal plates, share fragility and possess relatively few morphological characters that can be positively identified. This study depicts the species composition of unarmoured dinoflagellates collected from sites along the coasts of the Gulf of Mexico and the Mexican Pacific and includes their descriptions and illustrations. We identified a total of 25 species belonging to 13 genera and six families that were studied through various techniques using light and scanning electron microscopy. Seven new records for the Mexican Pacific are annotated here that include Amphidinium flagelans Schiller, Gyrodinium cochlea Lebour, G. glaebum Hulburt, G. metum Hulburt, Karenia selliformis Haywood, Steidinger et MacKenzie, Karlodinium ballantinum de Salas, and K. veneficum (Ballantine) Larsen. The genera Karenia and Karlodinium belong to the family Kareniaceae, characterised for encompassing the largest number of toxic species among the unarmoured dinoflagellates, and many species produce algal blooms around the world. Ceratoperidinium falcatum and Levanderina fissa are names recently proposed elsewhere as new taxonomic combinations and are also included here. The diversity of unarmoured dinoflagellates has been strongly underestimated in the past and the new records reported here confirm this. Further studies, including traditional and modern concepts and protocols (including molecular tools), should be undertaken in the near future to understand their real diversity.