From development to taxonomy: the case of (Monogenea: Microcotylidae) in the Mediterranean meagre.

The microcotylid is a pathogenic monogenean infecting , a candidate for species diversification in the Mediterranean aquaculture. Life-history stages of commonly co-occur in field infections, but to date, morphological data have only been provided for oncomiracidia and adults although identifying life-history stages can be useful in infection management. A total of 114 specimens of were analysed to characterize the developmental events and to assess morphological and morphometric variations before and after maturity. The post-larval development of is characterized by: expansion and bifurcation of the gut, loss of the larval haptor, protandrous development of the genitalia and vitellaria formation. The size variability of larval hooks, hamuli and germanium of is firstly reported and dimensional ranges of parasite body, haptor, testes, posteriormost clamps and eggs are widened. The size of most of the diagnostic features of significantly increases after parasite maturity and therefore, only those specimens with more than 116 clamps should be considered for minimising development-related variability in size. The high number of clamps, their fast development and the asymmetry in their size and arrangement suggest that may use a mixed attachment strategy between the closely related microcotylids and heteraxinids. This combination of features may be host related and linked to the gill structure of the sciaenid fish and the phylogenetic position of the genus ; distant from other microcotylids while close to heteraxinid species.