Ichthyastiotrema, 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 : 452-454

Ichthyastiotrema n. gen.

( Figs. 6–8 )

Type- and only species. Ichthyastiotrema fotedari ( Dhar, 1977) n. comb.

(Syns. Astiotrema fotedari Dhar, 1977 ; Astiotrema fusiformis [ Wang, 1981] Karar, Blend, Dronen & Adel, 2021 [Malformed suffix]; Astiotrema fusiforme [ Wang, 1981] Karar, Blend, Dronen & Adel, 2021; Gauhatiana fusiformis Wang, 1981 )

Etymology. The generic designation is based on the Greek word root “ichthys” meaning “fish” and refers to the restriction of hosts to a distinct group of fishes (i.e., Cyprinidae ) compared with that of Astiotrema (sensu stricto), wherein one species now composing this genus was originally considered.

Diagnosis. Body large, elongate to fusiform, mainly rounded at both ends or rounded anteriorly and tapered posteriorly. Tegument spinous. Forebody approximately 1/5 of total body length. Suckers subglobular, unspecialized. Oral sucker subterminal. Ventral sucker posterior to midpoint of first third of body, fairly smaller than oral sucker. Prepharynx absent. Pharynx well developed, smaller than both suckers. Esophagus short, narrow. Intestine bifurcates at mid-forebody. Ceca long, terminates a little anterior to posterior extremity. Testes two, intercecal, in middle third of body, globular to elliptical, tandem to oblique. Cirrus-pouch claviform, extends well into hindbody. Internal seminal vesicle large, unipartite; pars prostatica short, straight, tubular; ejaculatory duct tubular, short, indistinct; few glandular cells fill space around pars prostatica and upper aspect of seminal vesicle. Genital atrium small. Genital pore post-bifurcal, median to slightly submedian, immediately in front of ventral sucker. Ovary globular, intercecal, smaller than testes, pre-equatorial, entire, dextral, at base of cirrus-pouch or lateral to it. Canalicular seminal receptacle absent. Vitellarium follicular; fields long, extracecal to slightly over ceca; anterior extent of vitellarium to pharyngeal, pre-bifurcal or bifurcal levels; posterior extent terminates at blind ends of ceca or slightly further posterior. Uterus inter and post-cecal, extracecal in fully gravid specimens, fills most of hindbody posterior to ovary, extends to posterior extremity. Metraterm simple. Eggs numerous, unfilamented, tanned, unembryonated in uterus. Excretory vesicle not observed. Excretory pore terminal. In intestine of freshwater fishes ( Cyprinidae ); Eastern & Southern Asia.

Remarks. Karar et al. (2021) defined A. fotedari as one of eight species recognized within Astiotrema (sensu stricto) characterizing it by the following uniquely-combined features: extensive vitellarium, extending either from the level of the intestinal bifurcation or pharyngeal level, and terminating at the blind ends of the ceca or slightly further posteriorly; long ceca, terminating a little anterior to the posterior extremity; an ovary closer to the ventral sucker than to the anterior testis; and an oral sucker larger than the ventral one. In addition, G. fusiformis was synonymized with A. fotedari based on possessing the same overall morphology and host group ( Cyprinidae Rafinesque ) ( Karar et al. 2021). Dhar (1977) considered A. fotedari a plagiorchiid within Astiotrema whereas Wang (1981) placed his specimens in the Macroderoididae McMullen, 1937 . Karar et al. (2021) recognized A. fotedari within Astiotrema (sensu stricto) in the superfamily Plagiorchioidea (sensu lato) - neither a plagiorchiid nor a macroderoidid (see Pojmańska et al. 2008).

Karar et al. (2021, figs. 23–25) did not specify the absence of the canalicular seminal receptacle in A. fotedari as was postulated by Dhar (1977, figs. 1 & 2) in the original description (i.e., “receptaculum seminis apparently absent”; see also Wang 1981, fig. 7). The absence of the seminal receptacle herein contradicts the diagnosis of Astiotrema (sensu stricto) by Karar et al. (2021) as well as other previous diagnoses of this genus (see Yeh & Fotedar 1958; Pojmańska et al. 2008). Furthermore, we feel the presence or absence of the canalicular seminal receptacle represents a strong diagnostic feature for differentiating at the generic as well as higher levels. Thus, we find A. fotedari to be unique from all taxa of Astiotrema (sensu stricto) and its derived genera ( Homeoastiotrema and Plesioastiotrema ) by the absence of the seminal receptacle and its distinct host group ( Cyprinidae ). Besides the differential features mentioned earlier, A. fotedari is distinguished from species of Plesioastiotrema by a ventral sucker well-positioned posterior to the intestinal bifurcation and a post-bifurcal genital pore vs a ventral sucker directly ventral to the intestinal bifurcation and a pre-bifurcal genital pore. In addition, A. fotedari can be characterized from species of Homeoastiotrema by the former possessing a cirrus-pouch extending well into the hindbody to the ovarian level vs never surpassing the ventral sucker level; a short, straight pars prostatica with the same width along its length vs a fairly long, sigmoid pars prostatica, vesicular proximally and narrower distally; few glandular prostatic cells occupying a smaller space around the anterior aspect of the seminal vesicle and the pars prostatica vs numerous cells filling a large space within the cirrus-pouch; an ovary smaller than the testes vs the reverse; and an oral sucker larger than the ventral one vs a ventral sucker of a slightly larger size than the oral one.

Astiotrema fotedari exhibits a closer relationship to the Macroderoididae compared to other plagiorchioid families based on the combination of the following characteristics and available host-parasite data: (i) genital pore unarmed at level of ventral sucker; (ii) oral sucker without lateral muscular papillae or lappets; (iii) a large portion of the uterus reaches into the post-testicular region; (iv) external seminal vesicle absent; (v) parasitic in intestine of freshwater fishes; and (vi) this species shares a common locality (Asia) with macroderoidids (see Bray 2008e; Font & Lotz 2008). An important characteristic in macroderoidids is the presence of a uterine seminal receptacle usually, which may explain the absence of the canalicular seminal receptacle in A. fotedari (i.e., A. fotedari may possess a uterine seminal receptacle). Although there are highly similar morphological characteristics between members of the Macroderoididae and A. fotedari , the former possesses a bipartite seminal vesicle (see Font & Lotz 2008) (Note: the two taxonomically disputed macroderoidid genera Gauhatiana Gupta, 1953 and Pseudoparamacroderoides Gupta & Agrawal, 1968 have a sacciform, unipartite cirrus-pouch – see Font & Lotz 2008 and Truong et al. 2021, respectively; Discussion below). The difference in the nature of the seminal vesicle (bipartite vs unipartite) between highly morphologically similar taxa represents attributes that are mutually exclusive and may potentially put these taxa into two different families or even superfamilies as we have observed with some trematode keys (e.g., see Pojmańska et al. 2008; Tkach 2008). Accordingly, we believe that A. fotedari does not belong within the Macroderoididae . The Allocreadiidae Looss, 1902 may represent a potential family for A. fotedari based in its members’ similar morphology; in particular, the diagnosis of this family includes possessing a sacciform internal seminal vesicle and parasitizing the intestine of freshwater fishes (see Caira & Bogea 2005). However, allocreadiids are aspinose distomes and have a canalicular seminal receptacle which, in turn, contradicts the diagnosis of A. fotedari which has a spinose body and lacks a canalicular seminal receptacle. Thus, we find A. fotedari does not appear to be an allocreadiid either.

Based on the dissimilar morphological features observed in A. fotedari (particularly, the combination of the absence of a canalicular seminal receptacle and the presence of a sacciform seminal vesicle) as well as its distinct host group ( Cyprinidae ) when compared to that observed in macroderoidids, allocreadiids, Astiotrema (sensu stricto) and its derived genera ( Homeoastiotrema and Plesioastiotrema ), we believe A. fotedari to need its own genus, thus, we propose Ichthyastiotrema n. gen. within the Plagiorchioidea (sensu lato) to accommodate A. fotedari as its type-species, Ichthyastiotrema fotedari ( Dhar, 1977) n. comb.

Figures

FIGURES 6–8. Intra-specific variation observed in Ichthyastiotrema fotedari (Dhar, 1977) n. gen., n. comb. 6. I. fotedari (syn. Astiotrema fotedari Dhar, 1977), ventral view, redrawn from Dhar (1977, fig. 1). 7. I. fotedari, ventral view, redrawn from Dhar (1977, fig. 2). 8. I. fotedari (syn. Gauhatiana fusiformis Wang, 1981), dorsal view, redrawn from Wang (1981, fig. 7). Abbreviations:AT, anterior testis; BS, body spines; Ce, cecum; CP, cirrus-pouch; Eg, egg; Es, esophagus; GP, genital pore; Me, metraterm; OS, oral sucker; Ov, ovary; Ph, pharynx; PP, pars prostatica; PT, posterior testis; SV, seminal vesicle; Ut, uterus; VF, vitelline follicle; VS, ventral sucker. Scale bars: Fig. 6 = 500 µm; Fig. 7 = 500 µm; Fig. 8 = 500 µm.