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 Author Karar, Yasser F. M. Department of Zoology, Faculty of Sciences, New Valley University, Kharga, New Valley, Egypt. & Research Associate, Laboratory of Parasitology, Department of Ecology & Conservation Biology, College of Agriculture & Life Sciences, Texas A & M University, College Station, Texas 77843, U. S. A. Author Blend, Charles K. Corpus Christi Museum of Science & History, 1900 N. Chaparral St., Corpus Christi, Texas 78401, U. S. A. & Laboratory of Parasitology, Biodiversity Research & Teaching Collection, Department of Ecology & Conservation Biology, College of Agriculture & Life Sciences, Texas A & M University, College Station, Texas 77843, U. S. A. Author Dronen, Norman O. Laboratory of Parasitology, Biodiversity Research & Teaching Collection, Department of Ecology & Conservation Biology, College of Agriculture & Life Sciences, Texas A & M University, College Station, Texas 77843, U. S. A. & The Schubot Center for Avian Health, Department of Veterinary Pathobiology, College of Veterinary Medicine & Biomedical Sciences, Texas A & M University, College Station, Texas 77843, U. S. A Author Adel, Asmaa Department of Zoology, Faculty of Sciences, South Valley University, 83523 Qena, Egypt. text Zootaxa 2023 2023-05-12 5284 3 445 495 http://dx.doi.org/10.11646/zootaxa.5284.3.2 journal article 10.11646/zootaxa.5284.3.2 1175-5326 7929507 DA6684D9-508D-47A3-ACD9-D36A201086C3 Plesioastiotrema monticellii ( Stossich, 1904 ) n. comb. ( Figs. 1–3 ) (Syns. Distomum signatum of Monticelli, 1891 nec Dujardin, 1845 ; Astiotrema monticellii Stossich, 1904 ) Records. 1. Stossich (1904) ; 2. Dollfus (1957) ; 3. Timofeeva (1961) ; 4. Sharpilo & Iskova (1989) ; 5. Tkach et al . (2001) ; 6. Ruchin & Kirillov (2012) . Remarks. Plesioastiotrema monticellii n. comb. (syn. A . monticellii ) was incompletely described as Distomum signatum Dujardin, 1845 by Monticelli (1891) . Stossich (1904) re-examined the materials deposited by Monticelli and assigned them to Astiotrema as A. monticellii which, in turn, is presently reassigned as the type-species of Plesioastiotrema . From previous records of this species, only the anterior extent of the vitelline fields exhibited a slight range of variability where the follicles either reached the anterior border of the ovary ( Dollfus 1957 ), extended a little further to a point midway between the ovary and intestinal bifurcation ( Stossich 1904 ; Dollfus 1957 ) or the follicles extended to immediately posterior to the intestinal bifurcation ( Timofeeva 1961 ; Sharpilo & Iskova 1989 ). Madhavi & Rao (1972) reported a doubtful record of A . monticellii (= P. monticellii ) from the intestine of the Indian flap-shelled turtle, Lissemys punctata (Bonnaterre) ( Testudines : Trionychidae ), collected from an unidentified locality (we assume Asia). Lissemys punctata is restricted to Asian localities (e.g., Bangladesh , Burma , India , Nepal , Pakistan & Sri Lanka ) (see Uetz et al . 2022 ) and represents a known host for A . reniferum , Astiotrema odhneri Bhalerao, 1936 and Astiotrema cyclemysi Siddiqi, 1965 (see Gupta 1954 ; Agrawal 1966a ; Karar et al . 2021 ); whilst the other records of P. monticellii clarify the limit of its distribution to European localities and to parasitize only colubrid water snakes ( Stossich 1904 ; Dollfus 1957 ; Timofeeva 1961 ; Sharpilo & Iskova 1989 ; Tkach et al . 2001 ; Ruchin & Kirillov 2012 ). Based on the distinct and limited distribution of host groups, the distant localities, and the absence of both a complete morphological description and illustrations for the adult worms of Madhavi & Rao (1972) , we believe they misidentified their specimens. Accepted records of P. monticellii demonstrate its uniquity in morphology and limited locality (Europe) as well as its distinct host group (colubrid water snakes). FIGURES 1–3. Intra-specific variations observed in Plesioastiotrema monticellii ( Stossich, 1904 ) n. comb. 1. P . monticellii (syns. Distomum signatum of Monticelli, 1891 nec Dujardin, 1845 ; Astiotrema monticellii Stossich, 1904 ), ventral view, redrawn from Stossich (1904 , fig. 3). 2. P . monticellii (syn. A . monticellii ), ventral view, redrawn from Dollfus (1957 , fig. 3). 3. P . monticellii (syn. A . monticellii ), dorsal view, redrawn from Timofeeva (1961 , fig. 1). Abbreviations: AT, anterior testis; Ce, cecum; CP, cirrus-pouch; EP, excretory pore; Es, esophagus; EV, excretory vesicle; GP, genital pore; LC, Laurer’s canal; Me, metraterm; OS, oral sucker; Ov, ovary; Ph, pharynx; PP, pars prostatica; PT, posterior testis; SR, seminal receptacle; SV, seminal vesicle; Ut, uterus; VD, vitelline duct; V-D, vas-deferens; VF, vitelline follicle; VR, vitelline reservoir; VS, ventral sucker. Scale bars: Fig. 1 = 500 µm; Fig. 2 = 500 µm; Fig. 3 = 500 µm. Plesioastiotrema monticellii can be easily characterized within the new genus by the following combination of morphological features: (i) oral sucker larger than ventral one, (ii) vitelline field short, extends anteriorly to either ovarian level or level immediately posterior to intestinal bifurcation while posteriorly follicles terminate at mid-level of anterior testis, (iii) ceca short, terminate at level of inter-testicular space, and (iv) testes that are tandem and ellipsoid in shape.