Size and Shape: Very small cells (~10 µm long X 5 µm  wide), generally oval in shape with 2 equal apically inserted flagella and a short, but noticable haptonema.

Plastids and Pigments: P. parvum has 2 cup-shaped golden-brown plastids running the length of each side of the cell.  Pigments include chla and chlc.

Distinguishing features: P. parvum is the notorious "golden tide"  alga that has caused fish kills in brackish and fresh water systems in many parts of the world.  It is recognizable by its small size, golden color, and the short haptonema protruding from between the flagella.

Distribution: Worldwide in coastal brackish and inland fresh waters. 

Impact: Toxic to fish, no toxic effects on mammals have been reported.

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.

Johansson, N. and Granéli, E. 1999. Influence of different nutrient conditions on cell density, chemical composition and toxicity of Prymnesium parvum (Haptophyta) in semi-continuous cultures. J. Exp. Mar. Biol. Ecol. 239: 243-258.

Tillman, U. (2003) Kill and eat your predator: a winning strategy of the planktonic flagellate Prymnesium parvum. Aquatic Microbial Ecology. 32: 73-84