The cytology and ultrastructure of Chrysonebula holmesii lund (Chrysophyceae), with special reference to the flagellar apparatus

Abstract

Zoospores of the rare chrysophyte Chrysonebula holmesii have a phylogenetically advanced type of organization with no photoreceptor apparatus; terminally inserted flagella, the shorter of which is vestigial; a Golgi apparatus consisting of several dictyosomes; and, most characteristically, a massive asymmetrical skeletal microtubular root system, this being responsible for the unusual trihedral shape of the zoospores. As far as can be determined, C. holmesii is cytologically very similar to Hydrurus foetidus and it is suggested that both species should be included in the family Hydruraceae. Differences between the macroscopic appearance of the present material and that from the type locality may be due to differences in water chemistry, but microscopically the material agrees with the type description particularly in the way the vegetative cells form characteristic posterior threads. This species does not seem to produce cysts of the Hydrurus-type though it may appear to do so when the two species are growing in close proximity.