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 microretic ulatum Belch 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 di noflagellate with an anticlockwise apical groove encircling the apex. The v egetative cell and cyst features and the chloroplast structure and pigment composition are similar to those of the only two other known species formin g microreticulate cysts, the PSP-toxin producer Gymnodinium catenatum Graha m and the nontoxic Gymnodinium nolleri Ellegaard et Moestrup. Gymnodinium m icroreticulatum is also nontoxic, but the cysts (17-28 mu m in diameter) ar e much smaller and the vegetative cells (20-34 mu m long, 15-22 mu m wide) do not form chains and have a prominent, large nucleus positioned in the ep icone of the cell. The cingulum is a descending left spiral that is displac ed one fourth to one third the length of the cell with no torsion. DNA sequ encing of the D1-D2 region of the large subunit ribosomal RNA gene indicate s 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 includ es the type species Gymnodinium fuscum Stein.