Plesioastiotrema, Karar & Blend & Dronen & Adel, 2023

Karar, Yasser F. M., Blend, Charles K., Dronen, Norman O. & Adel, Asmaa, 2023, Towards resolving the problematic status of the digenean genus Astiotrema Looss 1900: Taxa excluded from Astiotrema (sensu stricto) with special reference to plagiorchioid genera closely related to the restricted concept of Astiotrema, Zootaxa 5284 (3), pp. 445-495 : 447-448

Plesioastiotrema n. gen.

Type-species. Plesioastiotrema monticellii ( Stossich, 1904) n. comb.

Etymology. The generic designation is based on the Greek word root “plesios” meaning “near” and refers to similarities the new genus has with members of Astiotrema (sensu stricto), wherein the two species now composing this new genus were originally considered.

Diagnosis. Body large, elongate to elongate oval, spatulate. Tegument spinous. Forebody approximately 1/4 of body length. Suckers subglobular, unspecialized. Oral sucker round, subterminal. Ventral sucker at border between first and second 1/4 of body, of roughly equal size with oral sucker or smaller. Prepharynx usually indistinct. Pharynx well developed, smaller than suckers. Esophagus fairly long, thin-walled, straight to slightly sinuous. Intestine bifurcates dorsal to ventral sucker in anterior part of second 1/4 of body. Ceca terminate in anterior portion of posterior half of body. Testes two, intercecal, smooth to slightly indented, tandem, elliptical to transversely elongate and separated by small inter-testicular space. Cirrus-pouch clavate, diagonal or slightly dextral to midbody line, extends distinctly into hindbody. Internal seminal vesicle large, thick-walled, unipartite, occupies most of space in cirrus-pouch; pars prostatica and ejaculatory duct short, tubular, indistinct from each other; no or few glandular cells apparent around pars prostatica or upper aspect of seminal vesicle. Genital atrium shallow, inconspicuous. Genital pore median to submedian, immediately anterior to ventral sucker, pre-bifurcal or at or near base of esophagus. Ovary globular to elliptical, intercecal, pre-equatorial, median to submedian, entire, at base of cirrus-pouch or lateral to it. Canalicular seminal receptacle distinct, post-ovarian, variable in size, elliptical to saccate. Vitellarium follicular; fields of variable length, extracecal and sometimes over ceca; anterior extent of vitellarium bifurcal or post-bifurcal; posterior extent pre-testicular or testicular. Uterus inter and post-cecal, fills most of hindbody posterior to ovary, extends to posterior extremity. Metraterm muscular, alongside cirrus-pouch. Eggs numerous, operculated, elliptical, unfilamented, tanned, unembryonated in uterus. Excretory vesicle Y-shaped. Excretory pore terminal. In intestine of colubrid water snakes and turtles; Europe & Southeast Asia.

Remarks. Astiotrema monticellii Stossich, 1904 was described by Stossich (1904) for specimens collected from the intestine of the viperine water snake, Natrix maura (Linnaeus) (syn. Tropidonotus viperinus Boie ) ( Squamata : Colubridae ) (type-host), from Naples, Italy. Stossich (1904) distinguished A. monticellii from Astiotrema reniferum ( Looss, 1898) Looss, 1900 and Astiotrema impletum ( Looss, 1899) Looss, 1900 by the position of the ventral sucker directly ventral to the intestinal bifurcation, the pre-bifurcal location of the genital pore and the shorter extent of both the ceca and vitellarium. Subsequent records of A. monticellii also indicated the unique position of the ventral sucker relative to the intestinal bifurcation as well as the pre-bifurcal position of the genital pore when compared with other taxa of Astiotrema (sensu latu) (see Dollfus 1957; Timofeeva 1961; Sharpilo & Iskova 1989). Astiotrema magniovum Fischthal & Kuntz, 1965 , was described by Fischthal & Kuntz (1965) for one specimen gathered from the large intestine of the Malayan soft-shelled turtle, Dogania subplana (Geoffroy Saint-Hilaire) ( Testudines : Trionychidae ), from Kasiqui, North Borneo. Astiotrema magniovum has the same two characteristics observed in A. monticellii : a ventral sucker directly ventral to the intestinal bifurcation and a pre-bifurcal genital pore. Astiotrema monticellii was reported from a distinct reptilian group, colubrid water snakes, and from close localities (e.g., Eastern Europe [ Ukraine & Russia] and south-central Europe [ Italy]) ( Stossich 1904; Dollfus 1957; Timofeeva 1961; Sharpilo & Iskova 1989; Tkach et al. 2001; Ruchin & Kirillov 2012). However, other species of Astiotrema , particularly those within the restricted concept, are known mainly from turtles, a few amphibians and fish, and monitor lizards distributed in Africa, Asia and Europe (see Karar et al. 2021). While A. magniovum parasitizes a turtle from the Trionychidae , a reptile family known to harbor some other species of Astiotrema (sensu stricto) (see Karar et al. 2021), it was recorded from Borneo, a relatively distant locality. Based on what we think in A. monticellii and A. magniovum are distinct generic-level morphological features as well as their widely separate localities ( Italy, Ukraine and Russia vs Borneo), we believe neither species to belong within Astiotrema (sensu stricto) and are in need of their own genus, thus, we propose Plesioastiotrema n. gen. for both species.