Size and Shape: Very large 50-80 µm long.  The epicone is rounded and the hypocone has 2 pointed lobes.

Plastids and Pigments: Numerous tiny red plastids distributed throughout the cell.

Distinguishing features: The brownish red color and the pair of lobes at the posterior end.

Distribution: Worldwide in brackish and marine  coastal waters.

Impact: Has been implicated in some fish kills, but is not believed to be toxic.  Mechanism of action appears to be physical congestion of gills during very dense bloom conditions.

References: 

Lewitus, A.J., Schmidt, L.B., Mason, L.J., Kempton, J.W., Wilde, S.B., Wolny, J.L., Williams, B.J., Hayes, K.C., Hymel, S.N., Keppler, C.J., and Ringwood, A.H. (2003) Harmful algal blooms in South Carolina residential and golf course ponds. Population and Environment. 24: 387-413.

 Daugbjerg, N., Hansen, G., Larsen, J., and Moestrup, O. (2000) Phylogeny of some of the major genera of Dinoflagellates based on ultrastructure and partial LSU rDNA sequence data, including the erection of three new genera of unarmored dinoflagellates.  Phycologia 39: 302-317.

Hulbert, E.M. (1957) The taxonomy of unarmoured Dinoiphyceae of shallow embayments on Cape Cod. Biol. Bull. 112: 196-219.