Anomalomacroderoiditrema, 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 : 480-481

Problematic status of Pseudoparamacroderoides Gupta & Agrawal, 1968 (sensu stricto) & Anomalomacroderoiditrema n. gen.

The taxonomic position of Pseudoparamacroderoides has fluctuated between the Macroderoididae and the Allocreadiidae , occasionally the Plagiorchiidae . Gupta & Agrawal (1968) assigned Pseudoparamacroderoides to the Walliniinae within the Allocreadiidae . Yamaguti (1971) reduced the rank of Pseudoparamacroderoides to the subgenus level within Paramacroderoides as a member of the Macroderoididae . Kumari et al. (1972) reassigned Pseudoparamacroderoides as a junior subjective synonym of Astiotrema in the Astiotrematinae Baer, 1924 from the Plagiorchiidae . Agarwal & Kumar (1983) retained Pseudoparamacroderoides as a subgenus of Paramacroderoides within the Macroderoididae , again. Agarwal & Agarwal (1984) retrieved the genus rank of Pseudoparamacroderoides as a distinct macroderoidid genus. Font & Lotz (2008) synonymized Pseudoparamacroderoides with Paramacroderoides whereas Tkach et al. (2010) revealed the substantial differences of members of Pseudoparamacroderoides and that of Paramacroderoides . As a result, they proposed synonymizing Pseudoparamacroderoides with Macroderoides since it is the morphologically most similar genus. Truong et al. (2021) resurrected and emended Pseudoparamacroderoides as a distinct genus within the Macroderoididae . As clarified earlier, the change in the nature of the seminal vesicle (either bipartite or unipartite) between highly morphologically close taxa represents contradictory attributes that could separate these taxa within two different families or even superfamilies. As Pseudoparamacroderoides (sensu stricto) and Anomalomacroderoiditrema possess a saccate, unipartite seminal vesicle, compared to the bipartite nature of this feature in other genera of the Macroderoididae (see Font & Lotz 2008), we believe, accordingly, that Pseudoparamacroderoides (sensu stricto) and Anomalomacroderoiditrema do not belong within the Macroderoididae . The Allocreadiidae may represent a potential family for both genera based on a high similarity in most diagnostic features (see Caira & Bogea 2005) except allocreadiids are aspinose trematodes whereas both genera in question have a distinctly spinose body. Therefore, we believe Pseudoparamacroderoides (sensu stricto) and Anomalomacroderoiditrema do not appear to be allocreadiids either.

Focusing on the characteristics of Pseudoparamacroderoides (sensu stricto) and Anomalomacroderoiditrema , we find strong similarities with taxa of Astiotrema (sensu stricto) and its closely related group of genera (i.e., those that have a unipartite, saccate seminal vesicle: Homeoastiotrema , Ichthyastiotrema , Kalipharynx , Longigula and Plesioastiotrema ); however, there are some differential features. Pseudoparamacroderoides (sensu stricto) is the most similar to Astiotrema (sensu stricto) except for the former having an I-shaped excretory vesicle and its host group restricted to bagrid catfishes ( Mystus , Sperata and Tachysurus Lacépède ) (see Truong et al. 2021; comments above) vs having a Y-shaped excretory vesicle and a wide variety of host groups, without any record of freshwater bagrid catfishes, in Astiotrema (sensu stricto) (see Karar et al. 2021).

With the absence of information regarding the excretory vesicle in Homeoastiotrema , Ichthyastiotrema and Kalipharynx , the distinction between Pseudoparamacroderoides (sensu stricto) and these three genera is limited. Ichthyastiotrema lacks a canalicular seminal receptacle and is restricted to cyprinid freshwater fish vs Pseudoparamacroderoides (sensu stricto) which possesses a canalicular seminal receptacle and is reported from freshwater bagrid catfishes. Homeoastiotrema is characterized from Pseudoparamacroderoides (sensu stricto) by five differential features: a cirrus-pouch in Homeoastiotrema that does not extend into the hindbody vs one extending well into the hindbody to near ovarian level in Pseudoparamacroderoides (sensu stricto); the pars prostatica is fairly long, sigmoid, vesicular proximally and narrower distally vs one that is short and straight with the same width along its length; the presence of numerous and distinct glandular cells filling a large space around the pars prostatica and anterior aspect of the seminal vesicle vs few glandular cells occupying a smaller space around the pars prostatica; a ventral sucker of slightly larger size than the oral one vs suckers roughly equal in size; and Homeoastiotrema parasitizes a distinct group of freshwater cichlids vs Pseudoparamacroderoides (sensu stricto) that parasitizes freshwater bagrid catfishes. Kalipharynx easily can be characterized from Pseudoparamacroderoides (sensu stricto) by possessing the following combination of features (see Boeger & Thatcher 1983; Pojmańska et al. 2008): the former having a distinctly large ventral sucker, about three times the size of the oral one vs the latter possessing nearly equally-sized suckers; ceca that overlap the ventral sucker dorsally vs ceca that do not overlap it; a papillate pharynx, equal in size with the oral sucker vs a non-papillate pharynx, smaller than both suckers; the posterior extent of the cirrus-pouch does not surpass ventral sucker level vs cirrus-pouch extends well into hindbody; a submedian, extracecal genital pore vs a median, intercecal one; an equatorial ovary equal in size to testes vs a pre-equatorial ovary, smaller than testes; and Kalipharynx parasitizes a distinct group of freshwater lepidosirenid lungfish vs records of Pseudoparamacroderoides (sensu stricto) from freshwater bagrid catfishes.

Regarding Longigula , it possesses papillae-like lateral lobes or ventrolateral lappets on both sides of the oral sucker, a post-equatorial ovary, a distinctly large distance separating the ovary from the ventral sucker, a Y-shaped excretory vesicle and it infects the intestine of geoemydid freshwater turtles (see Qiu et al. 1983; Tkach 2008). Pseudoparamacroderoides (sensu stricto) lacks any lateral lobes/lappets around the oral sucker, possesses a pre-equatorial ovary with a small distance separating the ovary from the ventral sucker, an I-shaped excretory vesicle, and is reported from freshwater bagrid catfishes. Plesioastiotrema is well-differentiated by having a ventral sucker directly ventral to the intestinal bifurcation, an esophageal genital pore, a Y-shaped excretory vesicle and it is found within a distinct reptilian group, colubrid water snakes, as well as from a trionychid freshwater turtle. In contrast, Pseudoparamacroderoides (sensu stricto) has a ventral sucker posterior to the intestinal bifurcation, a post-bifurcal genital pore, an I-shaped excretory vesicle and it is restricted to freshwater bagrid catfishes.

Concerning Anomalomacroderoiditrema , it is differentiated from Astiotrema (sensu stricto), Homeoastiotrema , Ichthyastiotrema , Kalipharynx , Longigula and Plesioastiotrema by the same features used earlier for differentiating Pseudoparamacroderoides (sensu stricto) from these aforementioned genera in addition to the four characteristics previously mentioned regarding Anomalomacroderoiditrema : a lobed ovary; a ventral sucker that overlaps the posterior portion of the intestinal bifurcation and left cecum at its origin; a submedian, extracecal genital pore, sinistral to the intestinal bifurcation; and the distinctive extent of the vitellarium – from pharyngeal level to a little anterior to the cecal extremities.

In conclusion, based on having a combination of features including the unipartite saccate internal seminal vesicle, I-shaped excretory vesicle, conspicuous spinose body, and distinct host group, our findings demonstrate Anomalomacroderoiditrema and Pseudoparamacroderoides (sensu stricto) are plagiorchioid genera morphologically closer to taxa of Astiotrema (sensu stricto) and its closely related group of genera ( Homeoastiotrema , Ichthyastiotrema , Kalipharynx , Longigula and Plesioastiotrema ). By contrast, our investigations exclude these two genera from the Allocreadiidae , the Macroderoididae , or any known family of the Plagiorchioidea . In other words, the family designation of these two genera remains uncertain, thus, we propose both to belong within the expanded concept of the Plagiorchioidea .