Gauhatiana Gupta, 1953

(Figs. 28 & 29)

(Syns. Gauhatinae Dayal & Gupta, 1953 [nomen nudum]; Gauhatiana Dayal & Gupta, 1954 [lapsus]; Gauhatiana Gupta, 1955 [lapsus])

Gauhatiana exhibits a relationship to members of the Opisthorchiidae Looss, 1899 based on its morphological structure and extent of the excretory vesicle (Y-shaped). However, Gauhatiana possesses a muscular cirrus pouch and the structure and position of its genital organs and coiled uterus originally placed Gauhatiana within the Fellodistomatidae Odhner, 1911 (= Fellodistomidae Nicoll, 1909) as a member of the Haplocladinae Odhner, 1911 (= Fellodistominae Nicoll, 1909) (see Gupta 1953). Skrjabin & Koval (1957) erected the Proctoecinae Skrjabin & Koval, 1957 within the Fellodistomatidae and reassigned Gauhatiana as one of its members. Yamaguti (1958) transferred Gauhatiana to the Walliniinae Yamaguti, 1958 within the Allocreadiidae. In their revision of Astiotrema, Yeh & Fotedar (1958) sunk Gauhatiana; they synonymized Gauhatiana with Astiotrema within the Plagiorchiidae and its type species, Gauhatiana batrachii Gupta, 1953, with A. reniferum. Agrawal (1966a) did not agree with Yeh & Fotedar (1958) in holding Gauhatiana to be synonymous with Astiotrema based on the difference in the appearance of the vitellarium; Gauhatiana has follicles distributed into two distinct aggregations (prebifurcal group and post-acetabular group) whilst vitellarium in Astiotrema forms one continuous, uninterrupted field.

Gauhatiana has undergone many taxonomic displacements being considered either in the Allocreadiidae or in the Macroderoididae McMullen, 1937 (see Mehra 1962; Skrjabin & Koval 1966, 1974; Gupta & Miglani 1974, 1976; Wang 1981; Prudhoe & Bray 1982; Wang et al. 1983) as a result of the confusion observed among the morphological characters of both families, particularly the lack of consensus regarding the diagnosis of the Macroderoididae which, in turn, has caused a noticeable change in either recognizing or not the validity of this family and/or what genera should be assigned to it (see Yamaguti 1958, 1971; Prudhoe & Bray 1982; Gibson 1996; de León 2001; Choudhury et al. 2002; Moravec & Salgado-Maldonado 2002; de León et al. 2007; Font & Lotz 2008; Pojmańska et al. 2008).

Font & Lotz (2008) pointed to a lack of distinctive features for differentiating between the Plagiorchiidae and the Macroderoididae with the exception of the shape of the excretory vesicle originally described by McMullen (1937); I-shaped in the Macroderoididae and Y-shaped in the Plagiorchiidae. However, Font & Lotz (2008) retained Gauhatiana tentatively within the Macroderoididae, in spite of its Y-shaped excretory vesicle, until a distinct consensus could be reached for distinguishing both families. Since Gauhatiana has a unipartite internal seminal vesicle and neither a bipartite nor a convoluted undivided tubular one, characteristic in members of both the Plagiorchiidae and the Macroderoididae, we do not consider Gauhatiana to be a plagiorchiid or a macroderoidid. Gauhatiana also has a distinct cirrus pouch unlike members of the Opisthorchiidae, which have a tubular, coiled seminal vesicle situated free in the parenchyma of the forebody (i.e., no cirrus-pouch) (see Scholz 2008), thus Gauhatiana does not belong among the opisthorchiids either.

Focusing on representatives of Gauhatiana, only four species have been reported: (i) the type-species, G. batrachii (syns. Gauhatinae batrachii Dayal & Gupta, 1953 [nomen nudum]; Gauhatiana batrachii Dayal & Gupta, 1954 [lapsus]; Orientocreadium batrachii [Dayal & Gupta, 1954] Arthur & Shariff, 2015 [lapsus]; Gauhatiana batrachii Gupta, 1955 [lapsus]), from the intestine of Clarias batrachus from the River Brahamputra at Guwahati, India; (ii) Gauhatiana lebedevi Gupta & Miglani, 1976 from the intestine of a marine teleost at Port Blair, India; (iii) G. fusiformis from the intestine of the yellowfin, Xenocypris macrolepis Bleeker (syn. Xenocypris argentea Günther) (Cypriniformes: Xenocyprididae), from Fujian Province, China; (iv) and Gauhatiana pseudobagri Wang in Wang, Zhao, Chen & Tao, 1983 from the intestine of the yellow catfish, Tachysurus fulvidraco (Richardson) (syn. Pseudobagrus fulvidraco [Richardson]) (Siluriformes: Bagridae), from Hongze Lake, China.

Karar et al. (2021) transferred the Chinese forms, G. fusiformis and G. pseudobagri, into Astiotrema as synonyms of Astiotrema fotedari Dhar, 1977 and A. reniferum, respectively, based on their lack of some characteristics of Gauhatiana, especially vitelline fields that are not distributed in two separate clusters on each side of the body. Based on the present study, G. fusiformis and G. pseudobagri have been reassigned – this time into I. fotedari and P. pseudobagri (see above).

Thus, Gauhatiana remains represented only by the two Indian forms, G. batrachii and G. lebedevi; both species similar to each other in morphology except G. lebedevi can be differentiated form G. batrachii by the latter having an oral sucker larger than the ventral one, the posterior extent of the cirrus-pouch exceeds the ventral sucker level, an equatorial to just post-equatorial ovary lying midway between the anterior testis and ventral sucker rather than closer to the anterior testis, a relatively short pars prostatica and a shorter space separating the ventral sucker from the intestinal bifurcation (see Gupta & Miglani 1976, figs. 1 & 2 vs Gupta 1953, figs.7 & 8).

Our investigations on digeneans infecting airbreathing catfishes, genus Clarias Scopoli, reveals that Gauhatiana is morphologically close to three plagiorchioid fluke genera: Astiotrema (sensu stricto) (Khalil 1959, 1969), Glossidium (e.g., Khalil 1972; Fischthal 1973; Mashego 1977; Moravec 1977; Mashego & Saayman 1989; van Rensburg et al. 2003) and Alloglossidium (Abdel-Maksoud 1998). Focusing on the characteristics of Gauhatiana, we found it shares with species of Astiotrema (sensu stricto) a combination of body plan morphology (particularly distome body plan), a unipartite vesicular seminal vesicle, host family they infect (Clariidae) and a common locality (India) when compared to Glossidium and Alloglossidium.

Gauhatiana is distinguishable from Glossidium, Alloglossidium and Astiotrema (sensu stricto) in addition to Alloastiotrema, Homeoastiotrema, Ichthyastiotrema, Longigula, Kalipharynx and Plesioastiotrema by possessing (i) vitellarium in two separated clusters in lateral fields (prebifurcal field and post-acetabular field) and an equatorial to just post-equatorial ovary; (ii) a large number of unicellular prostatic gland cells that occupy the entire space within the cirrus-pouch around the seminal vesicle, pars prostatica and ejaculatory duct; and (iii) the ejaculatory duct joins the terminal part of the uterus to form a well-developed globular genital atrium (i.e., “genital sinus”) (see Gupta 1953, fig. 7; Gupta & Miglani 1976, figs. 1 & 2).

The other genera mentioned have (i) vitellarium in one continuous uninterrupted field and a pre-equatorial ovary, (ii) few numbers of prostatic gland cells that occupy a small space around the pars prostatica and anterior border of the seminal vesicle as well as (iii) a weakly-developed genital atrium. Accordingly, we continue to adopt Gauhatiana as a distinct genus from Astiotrema (sensu stricto) and the derived, closely related genera Homeoastiotrema, Ichthyastiotrema and Plesioastiotrema.

Although workers have observed the morphological convergence of Gauhatiana within the Plagiorchioidea, our findings suggest that Gauhatiana represents a monorchioid taxon rather than a plagiorchioid one based on the combination of the following characteristics: parasite in intestine of a teleost; both suckers and pharynx present; mouth opens through an oral sucker; male and female ducts open separately into a well-developed genital atrium; prepharynx absent; testes two, post-ovarian; excretory vesicle Y-shaped with an excretory pore at the posterior extremity; cirrus-pouch present; vitellarium follicular, relatively small, with comparatively few follicles; spinose, unipartite body without a specialized holdfast organ; hermaphroditic sac absent; genital pore in forebody, anterior to ventral sucker; and an intestine with two ceca (Bray 2008 a, 2008c). Only the Lissorchiidae Magath, 1917 and the Monorchiidae are morphologically close monorchioids to Gauhatiana. The Lissorchiidae is restricted to monorchioid members that (i) parasitize freshwater fishes, (ii) possess a lateral or sublateral genital pore, (iii) have a tubular, I-shaped excretory vesicle, (iv) possess a genital atrium that is either weakly-developed or absent and (v) have a simple metraterm without a terminal organ (Bray 2008d). Members of the Monorchiidae include monorchioids that (i) parasitize marine and occasionally freshwater teleosts, (ii) have a median genital pore in the forebody, (iii) possess an excretory vesicle variable in shape (i.e., saccular, tubular, V- and Y-shaped), (iv) possess a distinct genital atrium and (v) have a terminal organ either absent or present as a simple or bipartite structure (Madhavi 2008). Accordingly, we reassign Gauhatiana within the Monorchiidae.

Concerning the representative subfamilies of the Monorchiidae, characteristics of Gauhatiana exhibit a combination of features confined between that of the Monorchiinae Odhner, 1911 and the Opisthomonorcheidinae Yamaguti, 1971 (see Madhavi 2008). Gauhatiana is distinguished from members of both subfamilies by the absence of a terminal organ and vitellarium distributed in two distinct clusters. Thus, we adopt Gauhatiana as belonging to the Monorchiidae, yet separate from all monorchiid subfamilies until future studies on Gauhatiana can help indicate its true taxonomic position.