Morphology and phylogeny of Gymnodinium trapeziforme sp.nov. (Dinophyceae): a new dinoflagellate from the southeast coast of Iran that forms microreticulate resting cysts

A new gymnodinioid dinoflagellate, Gymnodinium trapeziforme sp. nov. is described from laboratory cultures established by germination of microreticulate resting cysts collected along the southeast coast of Iran bordering the northern Oman Sea. The vegetative cells are small, biconical to ovoid, with a horseshoe-shaped apical groove that encircles the apex in an anticlockwise direction. Cells have a large tear-shaped nucleus positioned in the right side of the cell that extends from the epicone to the hypocone. Cells of G. trapeziforme can be clearly differentiated from the three other microreticulate cyst-forming gymnodinioids, Gymnodinium catenatum, Gymnodinium nolleri, and Gymnodinium microreticulatum by the shape and position of the nucleus. Cultures established from resting cysts do not produce detectable saxitoxin. The resting cysts of G. trapeziforme are unique in being cubic-trapezoidal in shape with a cyst wall colour that is pale purple-brown, most similar in colour to cysts of G. microreticulatum Bolch & Hallegraeff. Comparisons of partial large subunit ribosomal RNA gene sequences demonstrate that G. trapeziforme is allied with, but distinct from (> 12.4% sequence divergence) the other microreticulate cyst-forming gymnodinioid species.