Size and Shape: Cells are 20-30 µm long X 15-17 µm  wide, generally oval in shape with 2 flagella, inserted apically.  The trailing (recurrent) flagellum is slightly longer than the cell.

Plastids and Pigments: Many discoid golden-brown or yellow-brown plastids are packed into the cell.  Pigments include ChlA, ChlC1, C2, and fucoxanthin.

Distinguishing features: The plastids can be packed so tightly into the cell that they appear to be a single reticulated plastid.  Large, rod-shaped mucocysts are packed into the posterior of the cell.

Distribution: Worldwide in coastal brackish and marine waters. 

Impact: Toxic, produces a toxin known as fibrocapsin, responsible for massive fish kills in mariculture facilities in japan.  Has bloomed in coastal waters of the mid-Atlantic in the US.

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.

Hargraves, P.E. and L. Maranda. 2002. Potentially toxic or harmful microalgae
from the northeast coast. Northeastern Naturalist 9(1):81-120. 

Kahn, S., Arakawa, O., and Onoue, Y. (1996) Growth characteristics of a neurotoxin-producing chloromonad Fibrocapsa japonica (Raphidophyceae).  J. World Aquaculture Society 27: 247-53