Pseudoparamacroderoides dongthapensis Truong, Curran & Bullard

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 : 474

Pseudoparamacroderoides dongthapensis Truong, Curran & Bullard in Truong, Curran, Dutton & Bullard, 2021

( Fig. 24 )

Record. 1. Truong et al. (2021).

Truong et al. (2021) established P. dongthapensis for specimens infecting the intestine of the whiskered bagrid catfish, Mystus mysticetus Roberts ( Siluriformes : Bagridae ), from the Mekong River at Cao Lanh Fish Market, Dong Thap Province, Vietnam. This species was characterized from P. seenghali (and its synonym, P. vittati ) by the following features: i) a more elongate hindbody, more than twice the length of the forebody (2.2–2.6×) vs less than twice the length of the forebody in P. seenghali (1.4–1.9×); ii) a longer excretory vesicle extending anteriad beyond the anterior testis (49–55% of body length) vs a shorter one reaching the mid-level of the posterior or anterior testis (32–44% of body length) in P. seenghali ; iii) a uterus extending posteriorly into the post-cecal space near the posterior extremity of the body (very small post-uterine space ~1% of body length) vs P. seenghali which has a uterus restricted to the cecal space (post-uterine space ~10–13% of body length); iv) a shorter esophagus (6–12% of body length) vs a longer one in P. vittati (= P. seenghali ) (19% of body length); v) a cirrus-pouch extending posteriad to the ventral sucker vs restricted to the area around the ventral sucker, not surpassing its posterior margin in the original description of P. seenghali ; and vi) proportionally larger testes (diameter> 1/4 of maximum body width) vs a smaller value for this feature in P. vittati (= P. seenghali ) (diameter <1/5 of maximum body width) (see Gupta & Agrawal 1968; Kakaji 1969; Truong et al. 2021). As mentioned earlier, the change in the anterior extent of the excretory vesicle (i.e., whether it terminates at level of posterior testis or extends anteriorly to level of anterior one) is a dubious and not well-justified feature, however, the distinct allometric difference in length of the excretory vesicle as a percentage of body length in P. dongthapensis from that of P. seenghali we feel represents a justified differential feature between both species. The forebody/hindbody ratio of P. dongthapensis is distinctly different from that of P. seenghali , thus, constituting another valid differential feature. With the expansion in the range of esophagus length as a percentage of body length and the more posterior extent of the cirrus-pouch to the level of the ovary (as a consequence of synonymizing P. vittati with P. seenghali in concert with the intra-specific variation observed by Kumari et al. 1972), we find using both these features for differentiating P. dongthapensis from P. seenghali not to be informative due to the existence of these two features that are now within the range of variation we recognize within P. seenghali . Regarding proportionally larger testes in P. dongthapensis vs P. seenghali , we find it important to mention that this feature can be subject to variation due to differences in the degree of worm maturity as well as the degree of flattening during fixation. While Truong et al. (2021, p. 699) stated that their “live adult trematodes were … flame-killed on microscope slides using coverslips to restrain the specimens without putting pressure on the specimen[s] …”, the earlier studies of Gupta & Agarwal (1968) and Kakaji (1969) did not elucidate their fixing procedures for specimens collected (i.e., no way to determine if or to what degree specimens were flattened). Thus, while we cannot dispute the use by Truong et al. (2021) of allometric differences in testes size as a feature distinguishing P. dongthapensis from P. seenghali , in this instance, caution is advised here in using this measurement comparatively. We commend Truong et al. (2021, fig. 5) for their detail in describing and illustrating the distinguishing features in the male genital system of P. dongthapensis , yet these features were not included among the characteristics of P. dongthapensis used to distinguish it from P. seenghali . We concur with Truong et al. (2021) that P. dongthapensis represents a distinct species from P. seenghali , irregardless of their high morphological resemblance, same host group (bagrid catfishes, Mystus ), close food and feeding habits of hosts, and their main geographical region (South Asia). However, the differences in the features of their male terminal genitalia are worthy of note. These features are: i) the seminal vesicle in P. dongthapensis is approximately 51–53% of cirrus-pouch length vs approximately 31–32% of cirrus-pouch length in P. seenghali ; ii) the pars prostatica is longer than the ejaculatory duct, measuring 12–48% of cirrus-pouch length, in P. dongthapensis vs a pars prostatica that is shorter than the ejaculatory duct, about 12–19% of cirrus-pouch length, in P. seenghali ; and iii) P. dongthapensis has a bulbous, short ejaculatory duct, 15–20% of cirrus-pouch length vs a tubular, longer ejaculatory duct, 23–39% of cirrus-pouch length, in P. seenghali .

Figures

FIGURES 24 & 25. Pseudoparamacroderoides dongthapensis Truong, Curran & Bullard in Truong, Curran, Dutton & Bullard, 2021 and Pseudoparamacroderoides pseudobagri (Wang in Wang, Zhao, Chen & Tao, 1983) n. comb. 24. P. dongthapensis, ventral view, redrawn Truong et al. (2021, fig. 1). 25. P. pseudobagri (syn. Gauhatiana pseudobagri Wang in Wang, Zhao, Chen & Tao, 1983), ventral view, redrawn from Wang et al. (1983, fig. 4). Abbreviations:AT, anterior testis; BS, body spines; Ce, cecum; CP, cirrus-pouch; ED, ejaculatory duct; Eg, egg; EP, excretory pore; Es, esophagus; EV, excretory vesicle; GP, genital pore; OS, oral sucker; Ov, ovary; Ph, pharynx; PP, pars prostatica; PT, posterior testis; SR, seminal receptacle; SV, seminal vesicle; Ut, uterus; VD, vitelline duct; VF, vitelline follicle; VS, ventral sucker. Scale bars: Fig. 24 = 500 µm; Fig. 25 = 500 µm.