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-

4.2. Molecular barcoding for the distinction of Plectanocotyle spp .

In the taxonomy of Polyopisthocotylea, it is recurrent to distinguish species by the cox 1 divergence. Herein, in addition to the morphological differences, the four species of Plectanocotyle differ significantly by the divergence in their corresponding cox 1 sequences ( Table 3) especially

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given that the recent effort by Ayadi et al. (2022) encompasses molecular data of thoroughly identified specimens (with complete traceability of host i.e., barcoded hosts and deposited hologenophores) of all currently known members of the genus except P. gurnardi which was completed in this study.

According to WoRMS (2023), four species have been assigned the genus Plectanocotyle ( Table 7). Two species are known from Atlantic waters, P. elliptica Diesing (1850) (see below) from the white perch Morone americana (Gmelin, 1789) ( Moronidae ) from North America, Northwest Atlantic (Diesing, 1850); and P. gurnardi from the grey gurnard E. gurnardus ( Triglidae ) from Belgium, Northeast Atlantic ( Van Beneden and Hesse, 1863). Three species occur in Triglidae in the Mediterranean: P. lorenzii Monticelli (1899) from Trigla sp. , off Rovigno, Croatia ( Monticelli, 1899) while the remaining two were first described from the Western Mediterranean, with P. major Boudaya et al., 2006 from C. obscurus from Tunisia ( Boudaya et al., 2006) and P. lastovizae from C. lastoviza off Algeria ( Ayadi et al., 2022).

Generally, the interspecific and intraspecific variations of cox 1 sequences in Polyopisthocotylea ranged from 0.2 to 5.6% ( Bouguerche et al., 2019a,b). The divergence between P. gurnardi sensu stricto from the type-host E. gurnardus off Sweden (i.e., close to the type locality,

northeast Atlantic) and P. jeanloujustinei n. sp. (designated as P. cf.

gurnardi by Ayadi et al. (2022) surpassed the interspecific threshold. Moreover, the hosts are different ( C. lastovizae for P. jeanloujustinei n. sp. vs. E. gurnardus for P. gurnardi sensu stricto) and the type localities are distinct (western Mediterranean vs. northeast Atlantic).

In the present study, we also generated 28S rDNA sequences for P. gurnardi sensu stricto from Sweden. Unfortunately, fewer 28S rDNA sequences of Plectanocotyle are available in GenBank and limited to P. gurnardi from E. gurnardus from the U.K., northeast Atlantic ( Olson and Littlewood, 2002) and the same host off France, Western Mediterranean ( Jovelin and Justine, 2001); and a sequence designated as Plectanocotyle sp. from C. lastovizae also from off France, Western Mediterranean ( Jovelin and Justine, 2001). All isolates of P. gurnardi from the type-host E. gurnardus from the North Sea (from Sweden and the U.K.) and the western Mediterranean differed by one and 2 pb respectively, suggesting the presence of a single species P. gurnardi on E. gurnardi . Thus, the previous record of P. gurnardi on its type-host E. gurnardus in the western Mediterranean by Jovelin and Justine (2001) is highly likely accurate.

Overall, the presence of Polyopisthocotylea in distinct localities is not unusual and has been previously challenged by cox 1 barcodes. Consequently, the taxonomic and geographic status of several polyopisthocotyleans has been validated (see ( Hossen et al., 2022a, 2022b). Hossen et al. (2022b) demonstrated with cox 1 barcodes the presence of Allogastrocotyle bivaginalis both in Mediterranean waters, off Algeria (report by Bouguerche et al. (2019a,b)) and in Australian waters

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(Victoria) of the southwest Pacific. The authors also demonstrated the presence of Kuhnia scombri (Kuhn, 1829) and Pseudokuhnia minor (Goto, 1984) in ten locations along the coast of China (recorded by Yan et al. (2016)) and in Australian waters (Victoria) of the southwest pacific ( Hossen et al., 2022b). Similarly, the microcotylids Microcotyle algeriensis Ayadi, Gey, Justine & Tazerouti, 2016 and M. merche Víllora-Montero , P´erez-del-Olmo, Valmaseda-Angulo, Raga & Montero, 2023 has been demonstrated to occur both in the western Mediterranean and northeast Atlantic waters ( Víllora-Montero et al., 2023).

Most interestingly, a single 28S rDNA sequence of Plectanocotyle sp. from C. lastoviza off France differed from P. gurnardi from the northeast Atlantic by 3–4 % and from P. gurnardi from the same locality, France by 3% despite that the analyzed sequences correspond to a highly conserved region of the nuclear gene (28S rRNA) ( Table 4). Hence, Plectanocotyle sp. ex C. lastoviza off France is clearly not P. gurnardi . At that time, neither P. major nor P. lastovizae were described yet ( Ayadi et al., 2022; Boudaya et al., 2006), and the only available species in the genus was P. gurnardi , and given the high divergence in 28S rDNA, Jovelin and Justine (2001) were also accurate in not identifying their Plectanocotyle sp. as P. gurnardi . Unfortunately, there are no cox 1 sequences of Plectanocotyle sp. of Jovelin and Justine (2001) nor 28S rDNA for P. lastovizae and so far, P. gurnardi is the sole species of the genus for which both cox 1 and 28S rDNA are available.

Given that C. lastovizae from the western Mediterranean hosts two different species, P. lastovizae ( Ayadi et al., 2022) and P. jeanloujustinei n. sp., we cannot ascertain if Plectanocotyle sp. of Jovelin and Justine

(2001) is P. lastovizae or P. jeanloujustinei n. sp.