Taxonomy, phylogeny, biogeography, and ecology of Sabulodinium undulatum (Dinophyceae), including an amended description of the species

Samples of Sabulodinium undulatum Saunders et Dodge, the type species of the monospecific genus, were collected and characterized from Germany, Russia, Japan and Canada. This species has a laterally flattened, oval cell with a truncated apex and a dorsally pointing small episome. The dorsal margin of the hyposome has an undulating shape. A dorsal spine and/or antapical spine are sometimes present. The specimens of this heterotrophic species are 27.5–42.5 mm long and 18.5–36.0 mm wide, and have a theca with the plate arrangement apical pore complex (APC) 5′ 1a 6′′ 5c 4s 6′′′ 1′′′′. The shape of the dorsal theca is variable. The species distribution seems to be restricted to northern temperate regions. Sabulodinium undulatum occurred in all sandy eulittoral areas throughout the year and was also present in sandy sublittoral and supralittoral (beach) samples. The species can tolerate a broad range of temperatures and salinities. Sabulodinium occurred from -2.0 to +24.3°C and 4–35 salinity. It is likely that the observed variability in morphology and habitat reflect several varieties. We propose to establish three varieties within the species, namely S. undulatum var. undulatum, S. undulatum var. glabromarginatum, and S. undulatum var. monospinum. The systematic position of Sabulodinium is discussed in the context of comparative morphological and molecular phylogenetic data.