Pronoprymna petrowi Bray & Gibson 1980

Pronoprymna petrowi (Layman, 1930) Bray & Gibson, 1980 (Figure 1 (b))

Host. Clupea pallasii pallasii.

Site of infection. Intestine.

Locality. Off eastern shore of Kamchatka Peninsula (59°15ʹ6 N & 163°43ʹ9E) at a depth of 80 m.

Prevalence. 15 of 30 host specimens (50%).

Intensity of infection. 1–120 worms per host specimen.

Deposited material. Two paragenophores (IPEE RAS 14295).

Representative DNA sequences. A partial 28S rRNA gene sequence was deposited in Genbank (NCBI) as MT872204.

Description (based on a slightly macerated paragenophore). Body fusiform, length 1,018, maximum width 217 at level of ventral sucker, 21.3% of length. Tegument unarmed. Oral sucker cup-shaped, 98 × 126, length 9.6% of body length; oral opening subterminal. Ventral sucker 112 × 112, length 10.9% of body length. Sucker width ratio 1:0.89. Forebody 25.4% of body length. Prepharynx not detected. Pharynx 45 × 39, length 4.5% of body length. Oral sucker to pharynx width ratio 1:0.31. Oesophagus 87, 8.6% of body length. Intestinal bifurcation in posterior quarter of forebody. Caeca terminating at level of testes; post-caecal distance 43.9% of body length.

Testes two, entire, opposite, in anterior third of hindbody, separated from ventral sucker; left 116 × 70, length 11.3% of body length; right 105 × 63, length 10.3% of body length. Post-testicular region length 43.9% of body length. Cirrus-sac clavate, thin-walled, extending posteriorly slightly beyond ventral sucker, enclosing bipartite seminal vesicle, very small vesicular pars prostatica, and ejaculatory duct, 126 × 35, length 12.4% of body length. Genital atrium tubular. Genital pore median, anterior to ventral sucker.

Ovary trilobed, median, post-testicular, 126 × 88, length 12.4% of body length. Laurer’s canal not detected. Mehlis’ gland anterior to ovary. Uterus filling most of hindbody. Eggs 31 × 17. Vitellarium from two lateral compact oval masses, posterior to ventral sucker, left 91 × 49, length 8.9% of body length, right 70 × 45, length 6.9% of body length. Vitelline ducts wide, running towards median line of body, ventral to testes.

Excretory vesicle almost V-shaped; excretory pore terminal.

Remarks. Layman (1930) originally described Pr. petrowi under the name ‘ Monorcheides (?) petrowi ’ basing on specimens found in Osmerus dentex Steindachner & Kner, 1870 (Osmeridae) caught in the Peter the Great Bay (Japan Sea). The genus affiliation of this species has been repeatedly discussed by various authors (see reviews of Margolis and Ching 1965; Shimazu 2018). Combination with the generic name Pronoprymna was proposed by Bray and Gibson (1980). Sucker-ratio 1:0.89, oral sucker cup-shaped and the cirrus-sac extending beyond the posterior edge of the ventral sucker, as well as the general morphology of the cirrus-sac, position of the testes, the shape and arrangement of the ovary and the vitellarium indicate that our specimens belong to Pr. petrowi (compare with Margolis and Ching 1965; Shimazu 2018).