Morphological and molecular (<i>cox</i>1, 28S rRNA) data of <i>Microcotyle erythrini</i> Van Beneden &amp;amp; Hesse, 1863 <i>sensu stricto</i> (Polyopisthocotyla, Microcotylidae) infecting the gill lamellae of a marine sparid fish in the Western Med

The polyopisthocotylan Microcotyle erythrini was first described from the common pandora ( Pagellus erythrinus ) collected off Brest, Northeast Atlantic, and subsequently recorded from various sparid hosts across the Mediterranean. Recent studies combining morphometric and molecular data resolved this complex into distinct species, including M. isyebi from Boops boops and M. whittingtoni from Dentex dentex . Here, we investigate Microcotyle from Pagrus pagrus off Tunisia (Western Mediterranean), combining morphological and molecular barcodes (28S rRNA and cox 1). The cox 1 sequence divergence between Microcotyle from P. pagrus off Tunisia and M. erythrini sensu stricto from P. erythrinus in the Mediterranean was 0-3 %, suggesting the presence of a single species. Newly generated cox 1 sequences clustered with high support within the M. erythrini sensu stricto clade reported from P. erythrinus in France and Spain and P. pagrus in Spain and Algeria. Phylogenetic analyses based on partial 28S rDNA sequences corroborated this, as the newly generated 28S sequences of M. erythrini from P. pagrus off Tunisia clustered alongside isolates from P. pagrus and P. erythrinus across the Western Mediterranean. We also provide novel morphometric and anatomical data for M. erythrini sensu lato based on Adriatic specimens (Montenegro) and discuss host specificity patterns in Microcotyle spp. from the Mediterranean. These findings emphasize the importance of comprehensive taxonomic revisions and highlight the complexity of Microcotyle species associated with sparid hosts in the Mediterranean.