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
Authors: KARAR YASSER F. M. , BLEND CHARLES K. , DRONEN NORMAN O. , ADEL ASMAA 
Published: May 2023

The restricted concept of Astiotrema Looss, 1900 has been revised to include only eight species and various representative synonyms. However, several remaining taxa of Astiotrema (sensu lato) still need more inspection and scrutiny to determine their correct taxonomic position. Following a comprehensive review, four new genera are erected to accommodate some taxa excluded from Astiotrema (sensu stricto), three of which are closely related to this restricted concept of Astiotrema. Plesioastiotrema n. gen. is erected to accommodate Plesioastiotrema monticellii (Stossich, 1904) n. comb. (syn. Astiotrema monticellii Stossich, 1904) as the type-species and Plesioastiotrema magniovum (Fischthal & Kuntz, 1965) n. comb. (syn. Astiotrema magniovum Fischthal & Kuntz, 1965). Homeoastiotrema n. gen. is established for its type-species, Homeoastiotrema turneri (Bray, Van Oosterhout, Blais & Cable, 2006) n. comb., to accommodate Astiotrema turneri Bray, Van Oosterhout, Blais & Cable, 2006. Ichthyastiotrema n. gen. is erected with its type-species, Ichthyastiotrema fotedari (Dhar, 1977) n. comb. (syn. Astiotrema fotedari Dhar, 1977). A distinct morphologically and taxonomically distant taxon from Astiotrema (sensu stricto) is proposed in its own genus, Alloastiotrema n. gen. with its type-species, Alloastiotrema birmanii (Khan, Gul-E-Lala, Ghazi, Khatoon, Waheed & Khan, 2021) n. comb., to accommodate Astiotrema birmanii Khan, Gul-E-Lala, Ghazi, Khatoon, Waheed & Khan, 2021 and positioned distant from Astiotrema (sensu stricto). Astiotrema erinaceum (Poirier, 1886) Stossich, 1904, Astiotrema trituri Grabda, 1959 and Astiotrema (Biguetrema) tananarivense Deblock & Capron, 1962 are adopted synonyms of Galactosomum erinaceum (Poirier, 1886) Bittner & Sprehn, 1928, Neoastiotrema trituri (Grabda, 1959) Tkach, 2008 and Laiogonimus tananarivensis (Deblock & Capron, 1962) Fischthal & Thomas, 1968, respectively. Astiotrema lazeri El-Naffar, Saoud & Hassan, 1984 and Astiotrema gangeticus Gupta & Singh, 1985 nec Harshey, 1932 are synonymized with Glossidium pedatum Looss, 1899 and Orientocreadium batrachoides Tubangui, 1931, respectively. Based on its contradiction to the diagnosis of members of the Orientocreadiidae Yamaguti, 1958, we declare Orientocreadium lucknowensis Nigam, Chandra, Johri & Saxena, 2015 as incertae sedis. Longigula Qiu, Zhang & Li, 1983 and Kalipharynx Boeger & Thatcher, 1983 are morphologically closest to Astiotrema (sensu stricto) compared to members of the Plagiorchiidae Lühe, 1901 based on both genera possessing a cirrus-pouch with a unipartite, saccular seminal vesicle. The problematic status of Pseudoparamacroderoides Gupta & Agrawal, 1968 (sensu lato), the closest related genus to Astiotrema (sensu stricto), is discussed through evaluating the differential characteristics among listed species to indicate the extent of their validity and identifying the genuine species within this genus to re-evaluate the confusing and overlapping species to help understand their relationships with closely related plagiorchioids. Accordingly, only three species are recognized within Pseudoparamacroderoides Gupta & Agrawal, 1968 (sensu stricto): Pseudoparamacroderoides dongthapensis Truong, Curran & Bullard in Truong, Curran, Dutton & Bullard, 2021; Pseudoparamacroderoides pseudobagri (Wang in Wang, Zhao, Chen & Tao, 1983) n. comb. (syns. Astiotrema pseudobagri [Wang in Wang, Zhao, Chen & Tao, 1983] Karar, Blend, Dronen & Adel, 2021; Gauhatiana pseudobagri Wang in Wang, Zhao, Chen & Tao, 1983); and Pseudoparamacroderoides seenghali Gupta & Agrawal, 1968 (Syn. Pseudoparamacroderoides vittati Kakaji, 1969 n. syn.). Pseudoparamacroderoides raychaudhurii Agarwal & Kumar, 1983 is re-evaluated as Alloglossidium raychaudhurii (Agarwal & Kumar, 1983) n. comb. Anomalomacroderoiditrema n. gen. is erected for the type-species, Anomalomacroderoiditrema keni (Agarwal & Agarwal, 1984) n. comb., to accommodate specimens of Pseudoparamacroderoides keni Agarwal & Agarwal, 1984. Although the morphological convergence of Gauhatiana Gupta, 1953 within the Plagiorchioidea Lühe, 1901 has been suggested, it is neither a plagiorchiid nor a macroderoidid and does not appear closely related to Astiotrema (sensu stricto); it evidently is a member of the Monorchiidae Odhner, 1911. Alloglyptus Byrd, 1950 is taxonomically positioned as a gorgoderoid in the Allocreadiidae Looss, 1902, neither a plagiorchioid taxon nor closely related to Astiotrema (sensu stricto). The ambiguity of the seminal receptacle in some taxa of Astiotrema is discussed.