Piscianchitrema nilense, Dronen & Karar & Blend, 2020

Dronen, Norman O., Karar, Yasser F. M. & Blend, Charles K., 2020, A new genus and species of Anchitrematidae Mehra, 1935 (Digenea: Gorgoderoidea) in a freshwater fish from the River Nile at Qena, Egypt with amendation of the family, Zootaxa 4780 (2), pp. 367-378 : 370-371

Piscianchitrema nilense n. gen., n. sp.

( Figs. 1–3 )

Type host: Unidentified species of freshwater fish.

Type locality: River Nile , Qena, Egypt (26º9’51” N, 32º43’36” E) .

Site of infection: Intestine.

Type material: Holotype NHMUK 2020.4.24. 1, paratypes (2) NHMUK 2020.4.24.2-3, voucher (1) NHMUK 2020.4.24. 4.

Etymology: The species designation “ nilense ” refers to the River Nile where this new digenean was collected in Egypt.

Description: Based on 4 fully mature specimens. Body elongate-oval, holotype 3,744 (mean 3,448; range 3,268 –3,744) × 1,521 (1,128; 920–1,521); tegument armed with numerous small, thorn-like spines, concentrated in forebody, spines 9–10 long. Anterior end gradually tapers, forms moderately small, rounded anterior extremity; posterior end more broadly rounded; maximum width in middle one-third of body. Forebody 1,066 (915; 850–1,066), 28% (28%; 25–30%) of body length. Thick, continuous rim around the periphery of ventral aspect of distome most pronounced along forebody; lateral aspects of forebody composed of large internal patches of vacuolated, somewhat glandular cells that form pad-like structures similar to those of species of Pelopscreadium . Pre-oral lobe absent. Oral sucker spherical to slightly elongate-oval, moderately muscular, subterminal, 370 (340; 320–370) × 390 (378; 330–410). Ventral sucker spherical, sessile, smaller than oral sucker, 390 (321; 224–390) × 330 (313; 300–330), located approximately 30% of length of body from anterior end. Oral sucker/ventral sucker width ratio 1:0.9 (1:0.8; 1:0.7–1: 0.9). Prepharynx absent; pharynx spherical to slightly oval, indistinctly muscular, 133 (141; 132–150) × 165 (147; 132–165), anterior end extends into posterior aspect of oral sucker; esophagus short, 28 (23; 7–31) long; intestinal bifurcation situated about 50% of forebody length from anterior end; ceca simple, long, largely inter-testicular, extends close to posterior extremity; ani absent.

Testes longitudinally elongate, moderately to deeply lobed, side by side, largely extra-cecal, approximately 34% of body length from anterior end, close to lateral margins of body, widely separated by inter-testicular space, 400 (298; 130–400) long, 11% (9%, 4–12%) of body length; right testis, 790 (715; 550–830) × 470 (408; 380–470); left testis, 750 (718; 570–860) × 460 (363; 300–460). Cirrus sac large, delicate, nearly round, 240 (315; 240–390) × 370 (325; 260–370), 6% (8%; 6–10%) of body length, medially situated immediately anterior to ventral sucker, occupies approximately posterior 60% of distance between intestinal bifurcation and ventral sucker; cirrus sac contains relatively large, spined cirrus, short ejaculatory duct surrounded posteriorly by prostatic cells, short pars prostatica with few prostatic cells around anterior extent, extensive tubular seminal vesicle winds throughout bulk of cirrus sac. Vas efferens unite immediately posterior to cirrus sac; vas deferens embedded in layer of cells at entrance into posterior margin of cirrus sac, entrance located some distance dextral to body midline. Genital pore submedian, slightly dextral, located approximately 60% distance between anterior and posterior margins of cirrus sac, opens into distinct genital atrium through flower-like rosette of glands.

Ovary entire, round, 250 (207; 118–250) × 330 (257; 138–330), medial, immediately post-testicular, situated immediately posterior to midlevel of body approximately 54% of body length from anterior end. Post-ovarian space long, 1,405 (1,582; 1,405–1,752) long, 38% (46%; 37–53%) of body length. Laurer’s canal present, full extent not observed; canalicular seminal receptacle not observed. Vitellarium follicular, follicles 30–60 (51; 25–85) × 12–45 (41; 12–75), largely extra-cecal in lateral fields of posterior one-half of body, occupies approximately 78% of postovarian space length, terminate short of cecal ends, do not approach midline of body. Uterus extensively folded, uterine loops largely filling post-ovarian space with descending and ascending uterine limbs; metraterm long, 2,380 (2,139; 1,923–2,380) long, distinctly thick-walled, extensively convoluted, extends posteriorly from cirrus sac to level of anterior margin of ovary. Eggs oval, operculate, 21–26 (23; 18–26) × 15–17 (14; 13–18), numerous, often masking details of anterior aspect of post-ovarian space, typically not present in metraterm.

Excretory vesicle Y-shaped; excretory pore slightly subterminal, somewhat dorsal. Intestinal parasite in insectivorous-prone freshwater fish of northern Africa (currently known only from Egypt); species of fish unknown.

Remarks: The new species superficially resembles species of Anchitrema by having a spinose tegument; a short esophagus; long ceca; largely extra-cecal testes located laterally just posterior to the ventral sucker; an entire, nearly medial, post-testicular ovary; and the round anchitrematid type cirrus apparatus (see Fig. 3 ) located medially, immediately anterior to the ventral sucker and that contains the characteristically tubular and convoluted seminal vesicle. Additionally, the new species has suckers in the anterior one-third of the body; an oral sucker that is slightly larger than the ventral sucker; a spherical to slightly oval pharynx; a nearly medial genital pore that opens a short distance anterior to the ventral sucker between the intestinal bifurcation and ventral sucker; a Laurer’s canal; a strongly coiled uterus with ascending and descending limbs that fills the post-testicular space; a largely extra-cecal vitellarium in the posterior one-half of body that does not surpass the cecal ends; and our specimens lack a prepharynx and ani. Generally, the measurements of structures herein overlap with those of previously proposed species of Anchitrema . The only study that specifically mentions the presence of a metraterm (no measurements given) in a species of Anchitrema is that of Pande (1935) in a re-description of A. sanguineum ; however, our specimens and those examined from the Smithsonian Parasite Collection demonstrate the presence of a coiled metraterm that extends from the cirrus sac to about the anterior margin of the ovary. Piscianchitrema nilense n. gen., n. sp. has a much smaller body than A. sanguineum (3,268 –3,744 vs 6,000) and a distinctively thicker-walled metraterm that comprises 56–65% of body length vs 40% in previously described species of Anchitrema . The presence of the thick, continuous rim around the periphery of the distome along most of its extent; the lateral aspects of the forebody being composed of large internal patches of vacuolated, somewhat glandular cells that form pad-like structures that are strikingly similar to the “pelops” of species of Pelopscreadium ; the presence of a uterine seminal receptacle, and having a freshwater fish host distinguish this species from all other species in the family.

Due to the erection of the new genus and the fact that it has been over a decade since the last review/revision of this family of digeneans ( Pojmańska 2008), we have created keys to the 3 genera we recognize within the Anchit- rematidae as well as the six species we currently consider valid in Anchitrema ; Mujibia and Piscianchitrema n. gen. are monotypic. The key to genera is based on Pojmańska (2008).

Figures

FIGURES 1–3. Piscianchitrema nilense n. gen, n. sp. from a freshwater fish in Egypt. 1. Adult specimen, ventral view. 2. Terminal genitalia showing details of cirrus sac, ventral view. 3. Details of female genital complex, ventral view. Abbreviations: A, ventral sucker; C, cecum; E, newly-formed eggs; F, vitelline follicles; G, genital pore; M, Mehlis’ glands; O, oral sucker; Ov, ovary; P, prostatic cells; Ph, pharynx; R, uterine seminal receptacle; T, testes; U, uterus; V, seminal vesicle; Y, vitelline reservoir