Pseudoparamacroderoides Gupta & Agrawal, 1968

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 : 470-471

Pseudoparamacroderoides Gupta & Agrawal, 1968 as a controversial genus

In this section, we investigate the taxonomically problematic status of this genus via a detailed morphological study of each recognized species. This will involve comparing and evaluating the differential characteristics between each species to identify the valid species within this genus as well as accommodate those species we consider not to be congeneric.

The problematic status of features used for differentiating taxa of Pseudoparamacroderoides Gupta & Agrawal, 1968

Truong et al. (2021) resurrected and emendated Pseudoparamacroderoides as a distinctive macroderoidid genus negating it as either a subgenus of Paramacroderoides Venard, 1941 (see Yamaguti 1971) or a junior subjective synonym of Astiotrema (see Kumari et al. 1972), Paramacroderoides (see Font & Lotz 2008) or Macroderoides Pearse, 1924 (see Tkach et al. 2010). The diagnostic combinations of characteristics that supported this argument were: i) a prominent ventral sucker and a subspherical oral sucker lacking distinctively enlarged circumoral spines; ii) blind ceca terminating in the post-testicular space near the posterior extremity; iii) an elongate, densely spinous body; iv) a unipartite, saccate, internal seminal vesicle; v) a median to submedian genital pore immediately anterior to the ventral sucker; vi) a pre-testicular, submedian ovary abutting or posterolateral to the ventral sucker; vii) a blind-ending seminal receptacle that is lateral or posterolateral to the ovary; viii) follicular vitellarium, extending from the level of or slightly anterior to the ventral sucker to the mid post-testicular region; ix) an I-shaped, wholly post-ovarian excretory vesicle, terminating at the level of the testicular region; and x) records finding species of Pseudoparamacroderoides to infect the intestine of freshwater bagrid catfishes distributed in the Indian subcontinent and Southeast Asia ( Truong et al. 2021).

Five species are recognized within Pseudoparamacroderoides : Pseudoparamacroderoides dongthapensis Truong, Curran & Bullard in Truong, Curran, Dutton & Bullard, 2021; Pseudoparamacroderoides keni Agarwal & Agarwal, 1984 ; Pseudoparamacroderoides raychaudhurii Agarwal & Kumar, 1983 ; Pseudoparamacroderoides seenghali Gupta & Agrawal, 1968 ; and Pseudoparamacroderoides vittati Kakaji, 1969 (syn. Pseudoparamacroderoides vittatusi Kakaji, 1969 [malformed suffix]) ( Truong et al. 2021; WoRMS 2022c). In their review on the validity of features used to differentiate among the last four species, Truong et al. (2021) discussed some dubious and not well-justified features that had been adopted by authors in the original descriptions of these species. These features included i) ovary either contiguous or posterolateral to ventral sucker by a small distance; ii) change in seminal receptacle shape and position; iii) the slight disparity observed in anterior extent of the vitellarium (i.e., whether follicles terminate either at the level of the base of the ventral sucker or slightly anterior to it); iv) the extensive degree of either inter- or extra-cecal uterine coils; v) the indistinguishable proportional size of the suckers among these four species; and vi) presence/absence of a small prepharynx. Truong et al. (2021) attributed these slight variations to one or more combined factors, particularly, the low sample sizes used, fixation-induced variations, and the varying degrees of relaxation and flattening among the worms studied; we can add the different treatments (e.g., nature and structure of the stain, staining procedures, stain pre/post-treatment, type of dehydrating and clearing materials, dehydration periods, and handling efficiencies) used in preparation of specimens as well as the effect of varying degrees of worm maturity on growth and extension of some internal features. Truong et al. (2021) also stated that the narrative descriptions of these four species were less informative and in need of more paraphrasing while the published illustrations lacked sufficient detail to confirm their putatively unique features. Accordingly, the descriptions of P. keni , P. raychaudhurii and P. vittati were weakly differentiated from the type-species, P. seenghali , and, in fact, strikingly similar to each other (see Truong et al. 2021). Truong et al. (2021) still recognized these three species as distinct members within Pseudoparamacroderoides in addition to building a key to all five reported congeneric taxa based on other morphological features and morphometric measurements they thought to be more constant, not highly vulnerable to variabilities caused by different preparatory treatments and well-justified as differential features. These characteristics included i) variation in the anterior extent of the excretory vesicle, either to the level of the posterior testis or to the level of or beyond the anterior testis; ii) testes either less than 1/5 or more than 1/4 of maximum body width in diameter; iii) hindbody less or more than twice length of forebody; iv) ceca terminate at middle of post-testicular space or near posterior end of body; v) uterus extends posteriorly beyond cecal ends or not; and vi) a post-uterine space that is either more than 10% or less than 5% of body length.

Our investigations on the validity of the aforementioned features in the key by Truong et al. (2021) to the nominal species of Pseudoparamacroderoides (sensu lato) cast doubt on their stability and credibility as well as demonstrate their high potential versatility. Hence, we believe their effectiveness as differential features may be unjustified. This argument is based on three observations: 1) Very low sample size(s) used in the original descriptions without any further supplemental re-descriptions. Specifically, three mature and eight immature specimens recorded as P. seenghali (see Gupta & Agrawal 1968); a single specimen as P. vittati (see Kakaji 1969); three specimens of P. raychaudhurii (see Agarwal & Kumar 1983); four specimens of P. keni (see Agarwal & Agarwal 1984); and seven specimens of P. dongthapensis ( Truong et al. 2021) . These low numbers, particularly in the aforementioned first four species, make it virtually impossible to demonstrate intra-specific variation. Therefore, if more specimens had been collected to describe these species, it is highly possible that a wide range of intra-specific variation in the differential features authors used to differentiate among these species would have been observed making determination of con-specificity inconclusive. Thus, while we understand that authors may choose to describe a species from few individuals instead of waiting for more specimens, especially with rare material, we want to note that relying on slight differences among disputed characteristics (i.e., features lacking variation due to low intensities of infection) may lead to more confusion and complicate taxonomic considerations greatly. Some examples we noted for differentiating among taxa of Pseudoparamacroderoides included: the presence or absence of a short prepharynx; the difference in anterior extent of the vitellarium (from the base of the ventral sucker to slightly anterior to its upper margin); the slight change in the extension of cecal ends (either near the posterior extremity or slightly anterior); the posterior extent of the post-testicular uterine coils (terminate near the posterior extremity or slightly anterior) and by extension the change in length of the post-uterine space; positioning of testes relative to each other (opposite to oblique) and by extension the difference in length of the inter-testicular distance; esophagus straight or partially curved; shape of the seminal receptacle; and the slight change in the anterior extent of the excretory vesicle within the level of the testicular region (either at mid posterior testis level or extending to anterior margin of the anterior one), especially if the inter-testicular distance is small and not effective to create an obvious difference. We note that the differences in each feature are very slight, and with the inability to confirm such features as consistent via subsequent redescriptions, the probability that these differences reflect intra-specific vs species level variation is higher. 2) Degree of worm maturity, which reflects growth and distribution of several internal organs. This includes expansion of uterine coils, hence, the length of the post-uterine distance; size and density of vitelline follicles; distribution of vitellarium and, by extension, slight changes observed in the length of the anterior and posterior extent of vitellarium; egg size; testes diameter; body length and width; posterior extent of ceca; and the amount of spermatozoa, hence, seminal receptacle size and shape.As we have experienced with many digeneans studied, the aforementioned values increase and/or expand in fully mature specimens compared to either early adult or immature ones. Regarding the positioning of the testes relative to each other (i.e., oblique vs opposite), we have observed the testes position to change during maturation beginning within early mature or immature individuals up to fully mature conspecific adults. 3) Different treatments and handling efficiencies during specimen preparation. This includes the degree of relaxation of worms during fixation, different fixation process(es) and type (s) of fixative(s) used, the degree of applied flattening of specimens, varying staining processes employed, and inordinate dehydration of specimens which could cause distortion in the shape and distribution of internal organs and/or lack of some tegumental structures. For example, excessive pressure while flattening can cause distortion in the shape, diameter(s) and distribution of the body and internal organs casting doubt on the validity of corresponding morphometric measurements. In contrast, an absence of relaxation and/or flattening may lead to a lack of clarity or artificial absence of some internal structures resulting in an inaccurate determination of the actual size of internal organs and their distances between each other. Based on our experimental experience, insufficient or prolonged dehydration of specimens (mainly in 95% and/or absolute ethanol) can cause specimens to shrink to less than their actual size, alter the appearance of the body wall, its width, delicate genital structures, folding of body margins (particularly specimens delicate in thickness) and, resultantly, affect morphometric and allometric observations in addition to lessening resolution of contiguous structures such as the fine ducts of the male and female genital systems.”