Morphological and molecular study of n. sp. (Trematoda: Didymozoidae) gill parasite of from the central and western Mediterranean Sea.

The current study provides a morphological and molecular characterization of a new species of (Trematoda: Didymozoidae) infecting the dusky grouper, (Teleostei: Serranidae) from the Mediterranean Sea. A total of 279 dusky grouper specimens were examined for didymozoid gill parasites from the Mediterranean Sea between 1998 and 2020. New species differs from the most similar congeneric species by the rudiments of female reproductive organs in functional male specimens, and the seminal receptacle, Mehlis gland and accessory gland cells in functional female specimens, not observed in (Yamaguti, 1970), (Abdul-Salam, Sreelatha and Farah, 1990) and (Yamaguti, 1938), respectively. These species are also characterized by their different hosts and location within the host tissues, being from other geographical localities. Moreover, this is the first species reported in from the central and western Mediterranean Sea. Genetic analyses were performed on partial 28S and partial internal transcribed spacer-2 ribosomal RNA regions and the mitochondrial cytochrome oxidase 1 (cox1) gene by polymerase chain reaction. Comparison of genetic sequences of n. sp. with the available deposited sequences of 28S revealed that the new isolates cluster with several unidentified didymozoids and groups as a sister clade of the Nematobothrinae subfamily. Moreover, 28S and cox1 phylogenetic trees evidenced that Didymodiclinae is well separated from Didymozoinae and other gonochoric didymozoids. Following both morphological and genetic results, a key of identification for the genus is proposed.