Plectanocotyle spp

Cappelletti, Alice & Bouguerche, Chahinez, 2024, “ Something old, something new, something borrowed, and the oioxeny is true ”: description of Plectanocotyle jeanloujustinei n. sp. (Polyopisthocotylea, Plectanocotylidae) from the MNHN Helminthology collection with novel molecular and morphological data for P. gurnardi (Van Beneden & Hesse, 1863) (sensu stricto) from Sweden, International Journal for Parasitology: Parasites and Wildlife 23, pp. 100914-100914 : 100914-

4.3. Taxonomy of Plectanocotyle spp .

There are several ambiguities surrounding the type-species of the genus, P. elliptica , first described from a member of the Moronidae 174 years ago (in 1850), but was not found again since its original description, and its validity was thus questioned ( Ayadi et al., 2022; Price, 1961). One might be tempted to argue against this, by referring for example to the diclidophorid Flexophora ophidii Prost and Euzet, 1962 , first described from the snake blenny Ophidion barbatum Linnaeus, 1758 from off S`ete, France in 1962 ( Prost and Euzet, 1962), never reported since until Bouguerche et al. (2020) redescribed it based on newly collected specimens from the western Mediterranean, 58 years later.

Moreover, Price (1961) suggested that P. elliptica was described based on a mutilated specimen, and most importantly, it was suggested that either the host fish had been misidentified or the specimen had been mislabeled as to origin ( Price, 1961). Herein, following Ayadi et al. (2022), we consider, P. elliptica a species inquirenda.

Plectanocotyle caudata Lebour, 1908 was described from E. gurnardus in the U.K., northeast Atlantic ( Lebour, 1908). In the present study, 28S rDNA sequences of P. gurnardi sensu stricto from Sweden and those from the U.K., northeast Atlantic ( Olson and Littlewood, 2002) were identical between them and nested within a single clade. Thus, following Llewellyn (1941) we consider that P. caudata and P. gurnardi represent the same species and we formally herein synonymize the two species.

Another gap in the knowledge of the systematics of the genus Plectanocotyle was partially related to P. gurnardi , first described as Phyllocotyle gurnardi Van Beneden and Hesse, 1863 . Despite the extensive efforts by Llewellyn (1941) who investigated the taxonomy of P. gurnardi , transferred it consequently to the genus Plectanocotyle , and described its clamps and its adhesive mechanisms ( Llewellyn, 1956), there are no morphometrical data for P. gurnardi from the type-host and type locality, and it is the sole species of the genus for which molecular data are lacking. Additionally, morphometric data for P. gurnardi from the type-host and type locality were lacking. Consequently, in their revisions of the genus Plectanocotyle, Ayadi et al. (2022) took a conservative approach and identified their Plectanocotyle from C. lastovizae as P. cf. gurnardi .

Herein, despite the absence of published records of P. gurnardi from Swedish waters, the “old” T. Odhner’ s slide of P. gurnardi labeled as “ Phyllocotyle gurnardi ”, with some specimens collected by T. Odhner 126 years ago (in 1898) and found in the Invertebrate collections at the SMNH (Stockholm, Sweden) triggered this investigation as it hinted at the presence of P. gurnardi in Swedish waters of the Northeast Atlantic. As indicated in the early efforts by Justine et al. (2013), this study is another example of the importance of Museum collections for modern research. The sampling of the type-host E. gurnardus allowed to collect “new” specimens for DNA extraction and to extend morphometrical data. Therefore, we provide a redescription of P. gurnardi sensu stricto, and we expanded the molecular database for the genus by providing for the first time cox 1 and 28S sequences for P. gurnardi sensu stricto. Careful examination of the borrowed slides of P. cf. gurnardi from C. lastoviza from the Helminthology collections at the MNHN (Paris, France) revealed that P. cf. gurnardi from the western Mediterranean differs from P. gurnardi from the Northeast Atlantic by morphology and molecules, and P. cf. gurnardi was thus described as a new species, P. jeanloujustinei n. sp. Thus, Plectanocotyle gurnardi does not occur on C. lastovizae and is oioxenic to E. gurnardus while P. jeanloujustinei n. sp. is oioxenic to C. lastovizae .

Hence, by combining “ Something old ”, “ something new ”, and “ something borrowed ”, we described a new species; and we demonstrated that in Plectanocotyle , the “ oioxeny is true ”. To the best of our knowledge, Plectanocotyle is the only genus among the Polyopisthocotylea for which all known (or all valid) species have been characterised by both morphology and DNA. Plectanocotyle jeanloujustinei n. sp. is the only

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polyopisthocotylean species that had been differentiated from all its congeners based on cox 1 sequences as all four Plectanocotyle valid species, Plectanocotyle gurnardi , P. major , P. lastovizae and P. jeanloujustinei n. sp. were characterised by DNA barcoding.