Neoastiotrema trituri (Grabda, 1959) Tkach, 2008

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 : 463-464

Neoastiotrema trituri (Grabda, 1959) Tkach, 2008

( Fig. 17 )

(Syn. Astiotrema trituri Grabda, 1959 )

Records. 1. Grabda (1959a, 1959b); 2. Sharpilo & Iskova (1989); 3. Tkach (2008).

Remarks. Grabda (1959a) described A. trituri from the small intestine of the smooth, northern smooth or common newt, Lissotriton vulgaris (Linnaeus) (syn. Triturus vulgaris Dunn ) ( Caudata : Salamandridae ), from Lake Mamry in northeastern Poland. Astiotrema trituri was distinguished from all Astiotrema species by (i) the position of the posterior testis near the posterior extremity of the body and posterior to the ends of the ceca, (ii) the much smaller cirrus pouch, and (iii) very large eggs – “almost double-sized” (48–61; 54 × 25–31; 29). That same year, Grabda (1959b) elucidated that A. trituri has life-cycle patterns identical to that of members of the Plagiorchioidea and concluded that the first intermediate host was a pulmonate snail, the great ramshorn, Planorbarius corneus (Linnaeus) (syn. Coretus corneus [Linnaeus]) ( Gastropoda: Planorbidae ). The second intermediate hosts included some cladoceran species: Simocephalus exspinosus (De Geer) , Ceriodaphnia reticulata (Jurine) , Daphnia magna Straus ( Anomopoda : Daphniidae ) and Eurycercus lamellatus (Müller) ( Anomopoda : Eurycercidae ). The development of this parasite includes the formation of a sporocyst and a xiphidiocercaria. Molecular characterization by Tkach (2008) of some taxa of Astiotrema including A. reniferum , A. monticellii (= P. monticellii ), A. turneri (= H. turneri ) and A. trituri demonstrated that the first three taxa formed a monophyletic clade closest to the heterophyids in contrast to A. trituri which clustered very close to Plagiorchis Lühe, 1899 . Concerning A. trituri , it possesses a typical plagiorchiid-like bipartite seminal vesicle, whereas the other three species of Astiotrema (sensu lato) in the analysis of Tkach (2008) possess an undivided, sac-like seminal vesicle. Based on life-cycle patterns of A. monticellii (= P. monticellii ) examined by Shevchenko & Vergun (1960), Tkach (2008) referred that: (i) the first intermediate host of A. monticellii (= P. monticellii ) is the prosobranch (gilled) snail Bithynia leachii (Sheppard) ( Gastropoda: Bithyniidae ), not a pulmonate one as described for A. trituri ; (ii) amphibians serve as the definitive host for A. trituri (see Grabda 1959b) whereas amphibians represent intermediate hosts for A. monticellii (= P. monticellii ) ( Shevchenko & Vergun 1960); and (iii) the development of A. monticellii (= P. monticellii ) includes the formation of cercariae from the Pleurolophocerca group within rediae (see Shevchenko & Vergun 1960), which is typical for members of the Opisthorchioidea . As previous molecular phylogenetic analyses generally indicated that Astiotrema formed a monophyletic clade distinctly separate from all members of the Plagiorchioidea and that clade was, moreover, closer to the Opisthorchioidea ( Tkach et al. 2001; Olson et al. 2003), Tkach (2008) removed A. trituri from Astiotrema and transferred it into the Plagiorchiidae . Despite the high similarity between A. trituri and members of Plagiorchis , the position of the right posterior testis (near the posterior extremity and past the cecal ends) vs the left anterior testis (intercecal and separated from right posterior testis by numerous uterine coils) gave justification for separating A. trituri into its own genus, Neoastiotrema , with its type- and only species, N. trituri (see Tkach 2008).

Besprozvannykh et al. (2015) demonstrated that Shevchenko & Vergun (1960) most likely described a larva belonging to a member of the Opisthorchioidea and neither the cercaria nor the metacercaria of a species of Astiotrema . In addition, they clarified that the first intermediate host of A. odhneri is a pulmonate snail and not a prosobranch (gilled) one; whereas, the second intermediate host can include pulmonate snails, frog tadpoles, and small fish within which sporocysts and xiphidiocercariae develop, but neither rediae nor pleurolophocercariae form. Besprozvannykh et al. (2015, fig. 2) also demonstrated through 28S rRNA gene sequence data that Astiotrema species clustered away from the Plagiorchioidea and formed a monophyletic clade closer and in a basal position to the Opisthorchioidea . Thus, observations of life-cycle patterns by Besprozvannykh et al. (2015) point out a convergence between both Neoastiotrema and Astiotrema , whereas their phylogenetic results indicate a distant relationship between them. Accordingly, we conclude that: (1) reliance on life cycle patterns for differentiating between these two genera may not be useful; (2) without distinct morphological evidence, morphological data become more confusing and unconvincing for differentiating among morphologically similar taxa; hence, using molecular phylogenetic results and support may illustrate the degree of divergence or convergence and give an indicator for delimitations of species and/or higher ranks; (3) the bipartite vs unipartite nature of the seminal vesicle herein represents a stronger feature for differentiating between these two genera and it can be highly effective in differentiating at higher levels of taxonomy such as families or even superfamilies as stated by Pojmańska et al. (2008) and Tkach (2008).

Figures

FIGURES 17 & 18. Neoastiotrema trituri (Grabda, 1959) Tkach, 2008 and Orientocreadium batrachoides Tubangui, 1931. 17. N. trituri (syn. Astiotrema trituri Grabda 1959), ventral view, redrawn from Grabda (1959, fig. 1). 18. O. batrachoides (syn. Astiotrema gangeticus Gupta & Singh, 1985 nec Harshey, 1932), ventral view, redrawn from Gupta & Singh (1985, fig. 1A). Abbreviations: AT, anterior testis; Ce, cecum; CP, cirrus-pouch; Eg, egg; EP, excretory pore; Es, esophagus; ESV, external seminal vesicle; EV, excretory vesicle; GA, genital atrium; GP, genital pore; ISV, internal seminal vesicle; Me, metraterm; OC, ôtype complex; OS, oral sucker; Ov, ovary; Ph, pharynx; Pr.Ph, prepharynx; PP, pars prostatica; PT, posterior testis; SR, seminal receptacle; SV, seminal vesicle; Ut, uterus; VF, vitelline follicle; VS, ventral sucker. Scale bars: Fig. 17 = 500 µm; Fig. 18 = 500 µm.