Phylum Pyrrophyta
The Greek word pyrrhos, means flames, and phyton, means plant. There are about 130 genera in this group of unicellular microorganims, with about 2000 living and 2000 fossil species described so far. Pyrrophyta consist of mostly dinoflagellates and Cryptomonads. They live in seas and freshwaters, serving as food for invertebrates and sometimes cause water blooms and the destruction of fish.
Dinoflagellates
The name "dinoflagellate" refers to the forward- spiraling swimming motion of these organisms. They are free-swimming protists with two flagella, a nucleus with chromosomes, Golgi bodies, mitochondria, and chloroplasts. They have a cell covering formation, a theca, that differentiates them from other algae. The cells are either armored or unarmored, and armored species have thecae divided into plates made of polysaccharides or cellulose which are key features used to identify them. The cell covering of unarmored species is made of a membrane complex. The theca can be smooth and simple or laced with spines, pores and/or grooves and can be highly ornamented. Dinoflagellates have been claimed by both botanists and zoologists. They share features that are found in both plants and animals: they can swim, many have cell walls, and both photosynthetic and non-photosynthetic species are known.