Liliatrema, GUBANOV, 1953

Sokolov, Sergey, Frolov, Evgeniy, Novokreshchennykh, Semen & Atopkin, Dmitry, 2021, An opisthorchiid concept of the genus Liliatrema (Trematoda: Plagiorchiida: Opisthorchioidea): an unexpected systematic position, Zoological Journal of the Linnean Society 192 (1), pp. 24-24 : 24-

GENUS LILIATREMA GUBANOV, 1953

Diagnosis: With characters of family. Type species L. skrjabini Gubanov, 1953 .

The four subfamilies differ from the 12 (without the Pachytrematinae ) earlier established opisthorchiid subfamilies (see: Scholz, 2008) most clearly in the following features: the Liliatrematinae , by the presence of a specialized oral sucker, the uroproct and the genital sac without gonotyl; the Apophalinae, by the presence of a median permanent ventrogenital sac with a welldeveloped ventral sucker and two gonotyls, which arise dorsally close against the ventral sucker overhanging it ventrally; the Cryptocotylinae , by the presence of a median permanent ventrogenital sac with an anterior pocket and a rudimentary ventral sucker located on the large protractile bulge, but without gonotyl; the Euryhelminthinae , by the presence of a median permanent ventrogenital sac with a well-developed ventral sucker and an elliptical or reniform, largely parenchymatose gonotyl. In this updated concept, the family Opisthorchiidae has lost its former essential difference with respect to Heterophyidae , which was the presence of the genital or the ventrogenital sac [compare with Bray (2008)]. The opistorchiids with an unspecialized (in particular, unarmed) oral sucker and the median genital or ventrogenital sac – apophallines, cryptocotylines and euryhelminthines – differ from the heterophyids with the same features in the morphology of the ventral sucker or gonotyl (if any). The liliatrematines possess a combination of features, which does not occur among other opisthorchioids, namely, the presence of a uroproct and a funnelshaped oral sucker with a penta- or heptagonal distal end, whose dorsal edge is covered with a hood-like tegumental fold. At the same time, the differences between the Opisthorchiidae and the Cryptogonimidae , previously identified by Bray (2008), are still valid.

The phylogenetically based taxonomy of the Opisthorchioidea is still being developed. The current taxonomic model of this superfamily (see: Bray, 2008) is imperfect because of the polyphyly of the family Heterophyidae , which was revealed repeatedly by the nuclear DNA sequence analyses ( Olson et al., 2003; Sato et al., 2010; Thaenkham et al., 2011, 2012; Fraija- Fernández et al., 2015; Le et al., 2017; Kuzmina et al., 2018; Pantoja et al., 2018; Hernández-Orts et al., 2019; Kohl et al., 2019; Tatonova & Besprozvannykh, 2019; this study). The present study and that of Tatonova & Besprozvannykh (2019) are the first attempts to resolve this problem. However, a discussion of the concrete steps towards a further revision of the Heterophyidae is currently impossible, because out of the several early-branching groups of these trematodes, only one is statistically supported in different approaches of our phylogenetic analysis ( Figs 4A , 5A ).

The absence of molecular data for 10 (without the Pachytrematinae ) opisthorchiid subfamilies (see: Scholz 2008), a labile position of Liliatrema , Apophallus and Euryhelmis on 28S rDNA and 18S+28S rDNA-based trees, indicate that the proposed concept of the Opisthorchiidae is preliminary. In future, the subfamilies Apophallinae , Cryptocotylidae Euryhelminthinae and Liliatrematidae might yet be dissolved or reduced to the status of a tribe or subtribe. The current phylogenetic data and previously published materials (e.g. Thaenkham et al., 2012; Tatonova et al., 2020) cast doubt on the monophyly of the subfamily Opisthorchiinae . Thus, this subfamily needs revision.

Figures

Figure 4. Phylogenetic position of Liliatrema based on dataset of partial 28S rRNA gene sequences alignment. A, reconstruction with maximum likelihood algorithm using Bayesian nodal support; B, alternative topology of the Opisthorchiidae in Bayesian algorithm. The posterior probabilities less than 0.9 are not indicated. References for data retrieved from GenBank are listed in Table 1.

Figure 5. Phylogenetic position of Liliatrema based on dataset of 18S+28S rRNA genes sequences alignment. A, reconstruction with maximum likelihood algorithm using Bayesian nodal support; B, fragment of tree with topology of the Opisthorchiidae in Bayesian algorithm. The posterior probabilities less than 0.9 are not indicated. References for data retrieved from GenBank are listed in Table 1.