A phylogenetic assessment of Pronoprymna spp. (Digenea: Faustulidae) and Pacific and Antarctic representatives of the genus Steringophorus Odhner, 1905 (Digenea: Fellodistomidae), with description of a new species Author Sokolov, S. G. Author Shchenkov, S. V. Author Gordeev, I. I. text Journal of Natural History 2021 2021-06-16 55 13 - 14 867 887 http://dx.doi.org/10.1080/00222933.2021.1923852 journal article 10.1080/00222933.2021.1923852 1464-5262 5464733 6217E5D2-00FD-4135-A8DA-CDBAFACA529B Pronoprymna ventricosa ( Rudolphi, 1819 ) Poche, 1926 ( Figure 1 (a)) Host. Alosa volgensis . Figure 1. Paragenophores of Pronoprymna spp. (a) Pronoprymna ventricosa , ventral view; (b) Pronoprymna petrowi , ventral view. Scales: (a) 400 µm; (b) 200 µm. Site of infection. Intestine. Locality. Obzhorovo channel in the Volga River Delta , Russia ( 46°10ʹN , 49°13ʹE ) . Prevalence. 1 of 1 host specimen. Intensity of infection. 3 worms in the single infected host. Deposited material. Paragenophore (IPEE RAS 14296). Representative DNA sequences. A partial 28S rRNA gene sequence was deposited in Genbank (NCBI) as MT872203 . Description (based on a slightly macerated paragenophore). Body elongate oval, length 1,499, maximum width 350 at level of ventral sucker, 24.2% of length. Tegument unarmed. Oral sucker subglobular, 161 × 175, length 11.1% of body length; oral opening subterminal. Ventral sucker 189 × 196, length 13.0% of body length. Sucker width ratio 1:1.12. Forebody 30.9% of body length. Prepharynx very short. Pharynx 56 × 49, length 3.9% of body length. Oral sucker to pharynx width ratio 1:0.28. Oesophagus 126, 8.7% of body length. Intestinal bifurcation in posterior quarter of forebody. Caeca terminating at level of testes; post-caecal distance 48.8% of body length. Testes two, entire, opposite, in anterior third of hindbody, separated from ventral sucker; left 140 × 77, length 9.7% of body length, right 133 × 77, length 9.2% of body length. Post-testicular region length 40.1% of body length. Cirrus-sac clavate, thin-walled, extending posteriorly slightly beyond middle of ventral sucker, enclosing bipartite seminal vesicle, very small vesicular pars prostatica, and ejaculatory duct, 154 × 49, length 10.6% of body length. Genital atrium tubular. Genital pore median, anterior to ventral sucker. Ovary trilobed, median, post-testicular, 114 × 114, length 7.9% of body length. Laurer’s canal not detected. Mehlis’ gland anterior to ovary. Uterus filling most of hindbody. Eggs 22 × 15. Vitellarium from two compact oval masses, postero-lateral to ventral sucker, partly overlapping testes ventrally, left 147 × 84, length 10.1% of body length, right 168 × 70, length 11.6% of body length. Vitelline ducts wide, running towards median line of body, ventral to testes. Excretory vesicle almost V-shaped; excretory pore terminal. Remarks. Pronoprymna ventricosa (as Distoma ventricosum Rudolphi, 1819 ) was originally described from Alosa alosa (Linnaeus, 1758) (Clupeidae) caught in the Italian part of the Adriatic Sea ( Rudolphi 1819 ). Poche (1926) erected for this species an independent genus Pronoprymna . Kurochkin (1964) , who was the first to discover this parasite in the Caspian Sea, described it as a new species Orientophorus caspialosae Kurochkin, 1964 . Bray and Gibson (1980) synonymised O. caspialosae with P. ventricosa . The morphology of our specimens corresponds to the description of P. ventricosa by Bray and Gibson (1980) , i.e . body elongate oval, oral sucker subglobular, sucker-ratio 1:1.12 caeca terminating at level of testes, the testes entire and symmetrically opposed, the cirrus-sac thin-walled and lying dorsal to ventral sucker and extending posteriorly to about midlevel of it, internal seminal vesicle bipartite, genital atrium tubular, ovary trilobed and post-testicular, vitellarium from two compact masses, located posterolateral to ventral sucker.