The adult female of Ergasilus briani Markewitsch, 1933 (Crustacea: Copepoda) is redescribed using scanning electron and light microscopy. The taxonomic history of E. briani is reviewed. It is confirmed that E. briani and E. minor Halisch, 1934 are synonymous. The known distribution of E. briani in Britain is noted.

The life cycle of Ergasilus briani is shown to consist of six nauplius stages, five copepodid stages and the adults. Only the adult female is parasitic. The flee-living stages are described in detail. The presence of three aesthetascs on the antennules of all copepodid stages and the adult is noted for the first time. Unusual aspects of E. briani development include: the antennule is sexually dimorphic from copepodid IV onwards, the dimorphism being expressed in the numbers of setae present on the more proximal segments, and the first appearance of the male maxilliped is at the copepodid II stage. The endopodal setation of the male maxilliped is the maximum known within the Poecilostomatoida. The striking pigmentation of the developmental stages of ergasilids is noted and discussed.

In a flow photochemical process switching off the light source and monitoring the reaction composition as it leaves the photoreactor allows the effect of all irradiation times up to a...