Gymnodinium microreticulatum sp. nov. (Dinophyceae): a naked, microreticulate cyst-producing dinoflagellate, distinct from Gymnodinium catenatum and Gymnodinium nolleri

A new microreticulate cyst-producing dinoflagellate, Gymnodinium microreticulatum Bolch et Hallegraeff (Gymnodiniaceae), is described from laboratory cultures established from germinated cysts collected from Newcastle Harbour, New South Wales, Australia. The species is a small, ovoid to biconical dinoflagellate with an anticlockwise apical groove encircling the apex. The vegetative cell and cyst features and the chloroplast structure and pigment composition are similar to those of the only two other known species forming microreticulate cysts, the PSP-toxin producer Gymnodinium catenatum Graham and the nontoxic Gymnodinium nolleri Ellegaard et Moestrup. Gymnodinium microreticulatum is also nontoxic, but the cysts (17–28 μm in diameter) are much smaller and the vegetative cells (20–34 μm long, 15–22 μm wide) do not form chains and have a prominent, large nucleus positioned in the epicone of the cell. The cingulum is a descending left spiral that is displaced one fourth to one third the length of the cell with no torsion. DNA sequencing of the D1–D2 region of the large subunit ribosomal RNA gene indicates that the new species is genetically distinct (> 15% divergence) from but closely related to G. nolleri, G. catenatum, and several other gymnodinioid dinoflagellates with a horseshoe-shaped apical groove, a group that includes the type species Gymnodinium fuscum Stein.