Lamellodiscus louiseuzeti n. sp. (Monopisthocotyla: Diplectanidae: Lamellodiscinae): a parasite of Chaetodon hoefleri (Teleostei, Chaetodontidae) with distinct attachment organ morphology.

During a study on representatives of Diplectanidae (Monopisthocotyla) infecting Chaetodon hoefleri, a marine teleost from Senegal, we collected individuals belonging to a species of Lamellodiscinae, which showed a unique arrangement of the haptoral lamellodiscs, so far unreported in the literature, with the first lamella of the ventral lamellodisc open anteriorly, unlike the dorsal lamellodisc, which is closed. Due to this arrangement, we describe the species Lamellodiscus louiseuzeti n. sp.. Apart from the morphology of the lamellodiscs, the new species differs from its congeners by having a two-part male copulatory organ; one part featuring a well-developed distal hook and one, morphologically very variable, exhibiting a distal tongue-shaped part. Phylogenetic analyses of a concatenated alignment of partial 18S rDNA, ITS1, and COI sequences (1,315 bp), and a separate 28S rDNA alignment (882 bp) of this new species and other species of Lamellodiscinae with available DNA sequence data resulted in phylogenetic trees with congruent topologies that indicated three main lineages. These clades correspond to the morphological groups of Lamellodiscus suggested in previous studies. Based on phylogenetic analyses, L. louiseuzeti n. sp. forms a well-supported group with other species of Lamellodiscus. However, its internal phylogenetic position within the genus remains unresolved. We opted to consider L. louiseuzeti n. sp. a member of Lamellodiscus. We also emended the generic diagnosis to incorporate the new species and propose a new morphological group: Heterolamellae.