The chrysophytes (‘Golden Algae’) constitute a group consisting mainly of the classes Chrysophyceae and Synurophyceae. They have in common their unequal flagella (a long hairy flagellum and a short smooth one) and pigment composition with the brown fucoxanthin giving the chloroplasts the characteristic golden-brown colour. They form specific resting stages, stomatocysts, which have a silicified wall with a pore closed by a non-silicified stopper. The two classes diverge in the position of the flagella, chlorophyll composition, and in the way the silica scales are formed. Another class, the Phaeothamniophyceae, includes most coccoid and filamentous forms previously assigned to the Chrysophyceae (i.e. Phaeothamnion, Stichogloea), but these genera are still retained in the Chrysophyceae here. The small class Dictyochophyceae is represented by the radially symmetric pedinellids.

The chrysophytes number about 1000 species. Most are unicellular or colonial flagellates, predominantly occurring in freshwater plankton. This treatment includes about 120 species found in the British Isles. Most of the silica-scaled forms (family Paraphysomonadaceae and the class Synurophyceae require electron microscopy for identification and are not included; only treated are those species which can be identified by means of the light microscope).

Some genera include representatives that are not only phototrophic, but phagotrophic. Sometimes remnants of engulfed organisms are visible.

DOUBTFUL TAXON

Microglena butcheri J.H.Belcher 1966

Pl. 72I (p. 284)

The position of the genus is problematical and on the basis of electron microscope investigations (Coute´ and Preisig, 1981) it might belong perhaps to the Raphidophyta rather than to the Chrysophyta. This species is characterized by its thick periplast with small lenticular bodies. It has a single yellowish green chloroplast with an eyespot and a funnel-shaped, non-contractile reservoir behind which the large nucleus is located.