Dictyocha speculum

No direct toxic effects could so far be established. However, fish kills have occurred during D. speculum blooms and are thought to be due to oxygen depletion .

This species can occur as a naked and a skeleton bearing form. The skeleton usually has 6 spines. Both the naked and the skeleton bearing stages are motile.

The species is cosmopolitan and found in cold and temperate waters, both coastal and oceanic

Dictyocha speculum occurs in two growth forms: a naked, either mononucleated or multinucleated form and and a form bearing a silica skeleton. The skeleton of Dictyocha speculum has a regular and usually hexagonal shape although aberrant forms with incomplete rings and between 5-9 spines have been observed (Henriksen et al. 1993). The cells contain many yellow-brown chloroplasts.

Dictyocha speculum and other members of the family Dictyochaceae are extremely variable in shape.