Pronoprymna ventricosa Poche 1926

Pronoprymna ventricosa (Rudolphi, 1819) Poche, 1926 (Figure 1 (a))

Host. Alosa volgensis.

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.