taxonID	type	description	language	source
03F4878CFF95FFB74189FA04483F4FCA.taxon	description	Figs. 5, 6	en	Vlasenkov, Sergei A., Gordeev, Ilya I., Sokolov, Sergey G. (2025): Towards the molecular resolution of the bird digenean Hyptiasmus oculeus complex (Cyclocoelidae). Zootaxa 5729 (2): 264-282, DOI: 10.11646/zootaxa.5729.2.3, URL: https://doi.org/10.11646/zootaxa.5729.2.3
03F4878CFF95FFB74189FA04483F4FCA.taxon	materials_examined	Material examined: 43 hologenophores (gravid specimens) from the nasal sinuses of Eurasian Coots collected in Primorsky Krai (n = 19; IEE RAS 14385 – 14401), Orenburg Region (n = 10; IEE RAS 14402 – 14011), Kaliningrad Region (n = 6; IEE RAS 14012 – 14017), Tver Region (n = 3; IEE RAS 14018 – 14020) and Dagestan (n = 5; IEE RAS 14021 – 14025) examined using molecular techniques and light microscopy (n = 41), as well as molecular techniques and SEM (n = 2). Sequences deposited: PX 139296 (28 S rRNA gene; 1252 bp); PX 204806 – PX 204808 (nd 1; 436 – 462 bp); PX 204810 – PX 204819, PX 204821 – PX 204830 and PX 508525 – PX 508547 (cytb; 387 – 428 bp).	en	Vlasenkov, Sergei A., Gordeev, Ilya I., Sokolov, Sergey G. (2025): Towards the molecular resolution of the bird digenean Hyptiasmus oculeus complex (Cyclocoelidae). Zootaxa 5729 (2): 264-282, DOI: 10.11646/zootaxa.5729.2.3, URL: https://doi.org/10.11646/zootaxa.5729.2.3
03F4878CFF95FFB74189FA04483F4FCA.taxon	description	Description (measurements as min-max and mean in parentheses). Body lanceolate; length 6300 – 12075 (9602), maximum width 1250 – 2425 (1973) in middle of body. Tegumental surface pitted. Oral sucker rudimentary, oval to trapezoid, 125 – 360 (235) × 160 – 320 (247); mouth slightly subterminal. Ventral sucker rudimentary, rounded to oval, 45 – 90 × 53 – 90 (64 × 73). Sucker-width ratio 1: 0.2 – 0.4 (1: 0.3). Forebody 13.7 – 18.4 % (16.5 %) of body length. Prepharynx length 100 – 260 (190). Pharynx rounded to oval, 205 – 340 (295) × 200 – 340 (300). Oesophagus length 150 – 600 (392). Caeca simple, uniting near posterior extremity to form cyclocoel. Testes two, smooth, rounded to oval, intercaecal, median, tandem, separated. Anterior testis 340 – 1140 (714) × 360 – 1100 (682), usually in middle third of body, occasionally (in one specimen) in posterior third of body. Posterior testis 370 – 1000 (678) × 280 – 900 (624), in posterior third of body, either contiguous with or distinctly separated from cyclocoel. Intertesticular space 8.5 – 20.9 % (16.5 %) of body length. Posttesticular space 6.1 – 14.5 % (9.1 %) of body length. Cirrus sac elongate, length 580 – 1300 (918), representing 7.0 – 12.5 % (9.6 %) of body length, width 100 – 300 (209), median, proximal end bifurcal to strongly post-bifurcal; containing voluminous, saccular internal seminal vesicle, tubular, convoluted pars prostatica, ejaculatory duct and unarmed cirrus; opens into common genital atrium. Genital pore at level of posterior margin of oral sucker or midlevel of prepharynx, median. Ovary smooth, rounded to oval, 400 – 560 (488) × 320 – 820 (471), median, intertesticular, separated from both testes, usually smaller than both testes (in 30 specimens), less often larger than both testes (in four specimens) or only to anterior testis (in three specimens) or only to posterior testis (in four specimens). Postovarian space 15.4 – 22.2 % (18.1 %) of body length. Laurer’s canal absent. Oötype with Mehlis’ gland at level posterior margin of ovary or slightly anteriorly. Vitellarium follicular; follicles in two lateral longitudinal bands distributed along caeca, confluent posteriorly and not anteriorly. Anterior border vitelline bands slightly asymmetrical, slightly posterior to intestinal bifurcation; posterior border over cyclocoel. Uterus extensive, with extracaecal loops over more than 2 / 5 of body length; proximal part acts uterine seminal receptacle, distal part differentiated as weakly developed metraterm. Metraterm sinistral or dextral to cirrus sac, opens into common genital atrium. Eggs with miracidia, 70 – 103 (89) × 25 – 65 (39), usually only in uterine loops filling middle and posterior thirds of body; normally only free miracidia in loops occupying anterior third of body, occasionally (in one specimen) eggs with miracidia together with free miracidia in distal uterine loops. Excretory vesicle V-shaped; pore dorso-subterminal.	en	Vlasenkov, Sergei A., Gordeev, Ilya I., Sokolov, Sergey G. (2025): Towards the molecular resolution of the bird digenean Hyptiasmus oculeus complex (Cyclocoelidae). Zootaxa 5729 (2): 264-282, DOI: 10.11646/zootaxa.5729.2.3, URL: https://doi.org/10.11646/zootaxa.5729.2.3
03F4878CFF95FFB74189FA04483F4FCA.taxon	discussion	Remarks. Hyptiasmus oculeus was originally described based on adult specimens from the infraorbital sinus of the Eurasian Coot collected in Germany (Kossack 1911). According to Kossack (1911), this digenean species differs from other congeners in the position of the posterior testis (distinctly anterior to cyclocoel) and the proximal end of the cirrus sac (at the level of the posterior end of the intestinal bifurcation), and in the prepharynx to oesophagus length ratio (the former is shorter than the latter). According to Witenberg (1923), H. oculeus differs from other Hyptiasmus species primarily by its distribution of the uterine loops, particularly the more anterior position of distal extracaecal loops and complete filling of the post-testicular space with uterine coils. These features served as the basis for Witenberg (1923) to erect this species into a new genus Transcoelum. This author also described Transcoelum sigillum Witenberg, 1923 as a new species differing from T. oculeus only in having testes with diameter equal to (rather than smaller than) the intracaecal distance. However, many authoritative researchers recognise Transcoelum as a junior synonym of Hyptiasmus. (Bychowskaya-Pavlovskaya 1949: Feizullaev 1980; Kanev et al. 2002; Dronen 2007; Dronen & Blend 2015). Bychowskaya-Pavlovskaya’s (1949, 1953) morphological analysis of Western Siberian and Tajikistan isolates of H. oculeus demonstrated considerable variability in size of the testes and the position of the posterior testis relative to the cyclocoel, and the position of the proximal end of the cirrus sac relative to the intestinal bifurcation in this species, leading her to synonymise T. sigillum with H. oculeus. In terms of the uterine distribution, the position of the posterior testis relative to the cyclocoel, and position of the proximal end of the cirrus sac relative to the intestinal bifurcation our specimens align with the concept of H. oculeus as originally proposed by Kossack (1911) and later refined by Bychowskaya-Pavlovskaya (1949, 1953). According to Dronen & Blend (2015), H. oculeus is additionally characterised by a relatively long intertesticular space (14 % of the body length or more) and a relatively short cirrus sac (900 μm or less). The mean value of the intertesticular space length (16.5 % of the body length) in our specimens is comparable with the data given for H. oculeus by these authors. However, mean length of the cirrus sac in our specimens (918 μm) was slightly higher than the maximum value provided by Dronen & Blend (2015). In the original drawing of H. oculeus by Kossak (1911), the testes are depicted as larger than the ovary. Witenberg (1923), Bychowskaya-Pavlovskaya (1949), Szidat L & Szidat U. (1966) and Sey (1966) provided illustrations of specimens identified by them as H. oculeus with the testes are smaller than the ovary. Our data also indicate variability in the ratio of gonad size in this species. However, the ratio of gonad size in most digeneans from our material (the testes are larger than the ovary) corresponds to that in the specimen of H. oculeus sketched by Kossak (1911). Our digeneans possess rudimentary oral and ventral suckers. These structures were not indicated in the original description of H. oculeus or in any subsequent morphological characterizations of this species based on gravid specimens (e. g., Kossack 1911; Witenberg 1923; Edelényi 1974; Sitko et al. 2017). However, Bychowskaya-Pavlovskaya (1953) and Edelényi (1974) depicted a muscular organ in their drawings of H. oculeus, which is similar to the rudimentary oral sucker in our specimens. Our re-examination of gravid specimens from Helminthological Collections at ZIN RAS identified by Bykhovskaya-Pavlovskaya (1949, 1953) as H. oculeus confirmed the presence of rudimentary oral and ventral suckers in these specimens (Fig. 7). A rudimentary ventral sucker was also detected in H. oculeus specimens from Sitko et al. ’ s (2017) collection, additionally examined by these authors at our request (P. Heneberg, personal communication). These findings demonstrate that our specimens match H. oculeus in all key diagnostic characteristics while expanding the known morphology of this species.	en	Vlasenkov, Sergei A., Gordeev, Ilya I., Sokolov, Sergey G. (2025): Towards the molecular resolution of the bird digenean Hyptiasmus oculeus complex (Cyclocoelidae). Zootaxa 5729 (2): 264-282, DOI: 10.11646/zootaxa.5729.2.3, URL: https://doi.org/10.11646/zootaxa.5729.2.3
