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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-

Site of infection: Musculature.

Specimens deposited: Three voucher specimens, IPEE RAS 14286.

Representative DNA sequences: Two complete 18S rRNA gene sequences ( MT303881 and MT303882 ), two ribosomal ITS1 fragments ( MT624319 and MT624320 ) and two partial 28S rRNA gene sequences ( MT303944 and MT303945 ), 1981 bp and 2641 bp (1138 bp used for phylogenetic analysis) in length, respectively. There were no variable sites within either 18S rDNA, 28S rDNA or ITS1 rDNA.

Description (based on three whole-mounted excysted specimens and two SEM-studied specimens): Body elongate; length 2475–2941, maximum width 636–665 in anterior half of body. Tegument spinose; spines multipointed, becoming sparser toward posterior end of body. Eye-spot remnants at level of pharynx. Oral sucker terminal, funnel-shaped, 539–630 × 483–553, with pentagonal distal (outer) end. Dorsal edge of distal end of oral sucker covered with hood-like fold of tegument. Ventral sucker well developed, rounded, 203–214 × 207–210, recessed within tegumental crypt. Forebody 30.3–33.9% of body length. Prepharynx 119–154. Pharynx oval 161 × 105–112. Oesophagus 84–140. Intestine bifurcating distinctly anteriorly to ventral sucker. Caeca reaching posterior end of body, connecting to excretory vesicle, forming uroproct.

Testes two, rounded to suboval, entire or slightly indented, tandem, in posterior half of body; anterior testis 259–301 × 329–371, posterior testis 364 × 280– 315. Post-testicular region 18.8–21.7% of body length. Cirrus-sac absent. Seminal vesicle, pars prostatica with field of prostatic cells, and ejaculatory duct lying free in parenchyma. Seminal vesicle bipartite, with relatively short proximal portion and long distal portion, running dextral to ventral sucker. Pars prostatica vesicular, surrounded by field of prostatic cells. Ejaculatory duct short, connecting with genital atrium. Genital atrium short, opening dextro-submedially at base of genital sac. Genital sac with lip-like posterior wall overlapping anterior part of recessed ventral sucker; median.

Ovary trilobed, pretesticular and dextrosubmedial, 140–154 × 147–175. Seminal receptacle canalicular, saccular, mainly posterior to ovary. Laurer’s canal opening dorsomedially just posterior to ovary level. Oötype not observed. Mehlis’ gland extensive. Uterus pretesticular, running sinistrally to a ventral sucker, curving anteriorly to the sucker and opening in the genital atrium. Vitellarium follicular; anlage of follicles in two longitudinal lateral fields extending from level of pharynx to posterior extremity of body, overlapping caeca ventrally and dorsally, and confluent in the posttesticular region. Excretory vesicle Y- to T-shaped, extending to seminal receptacle.

Species 18S rRNA gene 28S rRNA gene Reference

Metorchis ussuriensis Besprozvannykh et al., 2019 – KY075772 Besprozvannykh et al. (2019)

Opisthorchiinae

Amphimerus ovalis Barker, 1911 AY 222121 AY116876 Olson et al. (2003)

Clonorchis sinensis (Cobbold, 1875) MK 450525 MK450525 Qiu et al. (2020)

Erschoviorchis anuiensis Tatonova et al., 2020 – MK877245 Tatonova et al. (2020)

Opisthorchis felineus (Rivolta, 1884) MF 077357 MF099790 Dao et al. (2017)

Opisthorchis viverrini (Poirier, 1886) JF 823987 JF823990 Thaenkham et al. (2011)

Outgroup

Isthmiophora hortensis (Asada, 1926) AB 189982 AB189982 Sato & Suzuki (2006)

Philophthalmus gralli (Mathis & Leger, 1910) JQ 627832 JQ627832 Literák et al. (2013)

METACERCARIA OF LILIATREMA SOBOLEVI GUBANOV, 1953

( FIGS 1B , 2 С–E, 3A)

Figures

Figure 1. Metacercariae of Liliatrema spp., whole view. A, L. skrjabini. B, L. sobolevi. Scale bars: 1 mm.

Figure 2. SEM microphotographs of Liliatrema spp. A, oral sucker of L. skrjabini. B, ventral sucker and genital sac of L. skrjabini. C, oral sucker of L. sobolevi. D, multipointed tegumental spines of L. sobolevi. E, ventral sucker and genital sac of L. sobolevi. Scale bars: A, C, 0.2 mm; B, 0.05 mm; D, 0.01 mm; E 0.1 mm.