Paraschistorchis, Blend & Karar & Dronen, 2017

Blend, Charles K., Karar, Yasser F. M. & Dronen, Norman O., 2017, Revision of the Megaperidae Manter, 1934 n. comb. (Syn. Apocreadiidae Skrjabin, 1942) including a reorganization of the Schistorchiinae Yamaguti, 1942, Zootaxa 4358 (1), pp. 1-44 : 13

Paraschistorchis n. gen.

Type-species: Paraschistorchis stenosoma ( Hanson, 1953) n. comb.

(Syn. Schistorchis stenosoma Hanson, 1953 )

Etymology: The generic designation is based on the Greek word root “ para ” meaning “beside, near or by” and refers to similarities the new genus has with members of Schistorchis sensu lato, wherein the four species now composing this genus were originally considered.

Diagnosis: Body elongate, maximum breadth at or near level of ventral sucker. Tegument spinous or unarmed. Eye-spot pigment present or absent. Forebody short, about a 1/5 to 1/3 of body length. Pre-oral lobe present or absent. Oral sucker subspherical to subquadrate, muscular, terminal to subterminal, simple with no anterior circumoral lobes; partial U-shaped muscular sphincter half-encircling oral aperture posteroventrally. Ventral sucker pre-equatorial, spherical, smaller than oral sucker. Prepharynx very short or absent, often inconspicuous. Pharynx longitudinally oval to nearly rectangular, well developed. Esophagus short or absent. Intestinal bifurcation at midforebody level or posterior to it. Caeca two, narrow to moderately wide, long, open via separate ani at posterior end of body. Testes 11 in number, arranged medially in one tandem row, smooth, ovoid to ellipsoidal to transversely elongate, separated to contiguous or nearly so, post-ovarian, distributed in posterior 1/2 to 2/3 of body. Posttesticular region short, less than 1/4 of body length. Seminal vesicle saccate or tubular, large, extends some distance into hindbody to about mid-ovarian level. Pars prostatica tubular, short, distinct, combines with distal portion of metraterm to form hermaphroditic duct which itself is short and extends anterodorsal to ventral sucker. Prostatic cells well-developed, free in parenchyma. Genital atrium distinct. Genital pore ventro-submedian (sinistral) to median, immediately anterior to or just overlapped by anterior margin of ventral sucker. Ovary spherical to subspherical, smooth, in hindbody, dextral, pre-testicular and separated or slightly contiguous with anteriormost testis. Canalicular seminal receptacle large, oval to elongate-oval to clavate, either sinistrolateral and slightly anterior to ovary or overlapping it. Mehlis’ gland dorsal to ovary or extending short distance anterior to it. Laurer’s canal well-developed, opens dorsally. Vitellarium follicular; distributed from near posterior extremity along lateral margins of worm into region between anterior testis and posterior margin of ventral sucker, confluent in posttesticular region; follicles profuse, small, lateral, dorsal and ventral to caeca. Uterus short, entirely pre-ovarian or extends to level of ovary or to just posterior to it, intercaecal. Metraterm distinct. Eggs relatively few, operculate, oval. Excretory vesicle I-shaped, moderately wide, median, extends anteriorly to posteriormost testis; primary excretory ducts (i.e. collecting tubules) run into forebody to terminate lateral to pharynx or oral sucker; excretory pore terminal or ventrally subterminal. In intestine of marine teleosts ( Tetraodontiformes & Perciformes ) in Indian and Pacific Oceans.

Remarks. Paraschistorchis n. gen. represents those four former Schistorchis species with a “simple” oral sucker and caeca that end in separate ani including Paraschistorchis longivesiculurus ( Hafeezullah, 1981) n. comb., Paraschistorchis seychellesiensis ( Toman, 1989) n. comb., Paraschistorchis stenosoma ( Hanson, 1953) n. comb. (type species) and Paraschistorchis zancli ( Hanson, 1953) n. comb.