Which of the following statements about dinoflagellates is true? Select one: A. All known varieties are autotrophic. B. Their walls are usually composed of silica plates. C. Many types lack mitochondria. D. Some produce toxic agents in the water E. Their dead cells accumulate on the seafloor, and are mined to serve as a filtering material.

The correct option is D(Some produce toxic agents in the water).

Explanation:

Dinoflagellates are found in the phylum Dinoflagellata which are single celled organisms. They are mostly found in the ocean while few of them can live in streams, freshwater ponds and rivers. The following characteristics can be used to identify a Dinoflagellates, these include:

--> they are golden brown

--> they possess assimilative cell with indented waist.

--> they possess large nucleus with visible chromosomes.

It has been reported that many dinoflagellate species can produce various natural toxins. These toxins can be extremely toxic and many of them are effective at far lower dosages than conventional chemical agents. Therefore the option, Some produce toxic agents in the water, is a correct statement.