introductionMonogenea is a class of ectoparasitic flatworms on the skin, gills, or fins of fish. Microcotylidae is a family of polyopisthocotylean monogeneans parasitising only marine fishes. This work describes and taxonomically determines a microcotylid polyopisthocotylean monogenean in an important fish in Saudi aquaculture. MATERIAL AND

methodsThirty gilt-head sea bream captured alive from the Red Sea of Saudi Arabia were examined for monogenean infection. Worms were described morphologically and morphometrically by light microscopy and multiple sequence alignments and phylogenetic trees were also constructed after maximum likelihood analysis of the 28S rRNA sequences.

resultsSeventeen fish were infected by a monogenean parasite in the gill lamellae. It showed a bilobed anterior extremity, two rows of numerous unequal clamps of microcotylid type, and paired muscular vaginae crowned by differently sized spines. The vaginal number and its relative armature suggested the species' affiliation to group D; the parasite possessed large, muscular vaginae with a full corona of spines over almost the entire width resembling

conclusionThe results confirmed the taxonomic status of the parasite recorded. On the basis of morphology and molecular data, we consider that several conclusions on the systematic status of microcotylids from Red Sea fishes in Saudi Arabia should be discussed.