Plesioschistorchis, 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 : 14-15

Plesioschistorchis n. gen.

Type-species: Plesioschistorchis callyodontis ( Yamaguti, 1942) n. comb.

(Syn. Schistorchis callyodontis Yamaguti, 1942 )

Etymology: The generic designation is based on the Greek word root “ plesios ” meaning “near” 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 either at level of ventral sucker or ovary. Tegument unarmed. Eye-spot pigment present or absent. Forebody short, about a 1/6 to 1/3 of body length. Pre-oral lobe present or absent. Oral sucker spherical to subspherical, muscular, subterminal, simple with no anterior circumoral lobes; partial U-shaped muscular sphincter half-encircling oral aperture posteroventrally. Ventral sucker pre-equatorial, spherical to subspherical, can be equal to oral sucker or slightly larger or smaller in size. Prepharynx very short or absent, often inconspicuous. Pharynx transversally oval to subquadrate, can be quite large, well developed. Esophagus short or absent. Intestinal bifurcation at mid-forebody level or slightly posterior it. Caeca two, narrow to moderately wide, long, terminate blindly near posterior end of body. Testes 11 in number (exceptionally 5), arranged medially or submedially in either one or two straight or zig-zag rows, smooth to slightly indented, subglobular to oval, separated to contiguous or nearly so, post-ovarian, distributed in posterior 2/3 of body. Posttesticular region short, less than 1/3 of body length. Seminal vesicle saccate or tubular, large, extends some distance into hindbody in region between ventral sucker and ovary or short distance posterior to ovary. Pars prostatica tubular, short, distinct or indistinct, combines with distal portion of metraterm to form hermaphroditic duct which itself is very short to moderate in length and proximate to anterior portion of ventral sucker. Prostatic cells welldeveloped, free in parenchyma. Genital atrium distinct. Genital pore ventro-submedian (sinistral) to median in forebody, either immediately anterior or anterolateral to or just overlapped by anterior margin of ventral sucker. Ovary ovoid, spherical to subspherical, smooth, in hindbody, median to dextral, pre-testicular and separated from anteriormost testis. Canalicular seminal receptacle large, oval to elongate-oval to retort in shape, either sinistrolateral to ovary or overlapping it. Mehlis’ gland dorsal, sinistral or immediately anterior to ovary. Laurer’s canal present, opens dorsally. Vitellarium follicular; distributed anteriorly in region between testes and posterior margin of ventral sucker, runs uninterrupted along lateral margins to posterior extremity, confluent in posttesticular region; follicles numerous, small, lateral, dorsal and ventral to caeca. Uterus pre-ovarian, with moderate to wide loops, intercaecal. Metraterm distinct. Eggs numerous, operculate, oval to ellipsoidal. Excretory vesicle Ishaped, moderately narrow to wide, median, extends anteriorly into area within anterior half of testes; primary excretory ducts (i.e. collecting tubules) cross caeca ventrally and run into forebody as far as oral sucker; excretory pore terminal. In intestine of marine teleosts ( Perciformes ) in Pacific and Indian Oceans.

Remarks. Plesioschistorchis n. gen. contains those four former Schistorchis species with a “simple” oral sucker and caeca that end blindly including Plesioschistorchis callyodontis ( Yamaguti, 1942) n. comb. (type species), Plesioschistorchis haridis ( Nagaty, 1957) n. comb., Plesioschistorchis manteri ( Gupta & Tandon, 1984) n. comb. and Plesioschistorchis sigani ( Yamaguti, 1942) n. comb.

From our investigations of schistorchiines collected from the Red Sea off Egypt as well as from the literature- and photography-based, morpho-taxonomic studies of accepted schistorchiine genera discussed above, we now offer a revised key to the Schistorchiinae which includes the two new genera we have erected as well as Schistorchis sensu stricto.

Key to genera of Schistorchiinae Yamaguti, 1942 (based on Cribb 2005 and present study)

1a. Two testes.......................................................................................... 2. 1b. Five or more testes (11 testes most frequent number)........................................................ 3.

2a. Caeca open independently via separate ani; oral sucker highly glandular...................................................................... Sphincteristomum Oshmarin, Mamaev & Parukhin, 1961 (Syn. Lobatotrema Manter, 1963 ).

2b. Caeca unite and open via a uroproct; oral sucker normally muscular (not glandular)...... Sphincterostoma Yamaguti, 1937 .

3a. Oral sucker highly glandular.. Schistorchis Lühe, 1906 (Syns. Megacreadium Nagaty, 1956 ; Schistorchis [Alloschistorchis] Yamaguti, 1970; Schistorchis [ Schistorchis ] Lühe, 1906).

3b. Oral sucker normally muscular (not glandular)............................................................. 4.

4a. Caeca open via a uroproct....................................... Neomegacreadium Machida & Kuramochi, 1999 .

4b. Caeca either open via separate ani or end blindly........................................................... 5.

5a. Caeca end in separate ani............................................................ Paraschistorchis n. gen.

5b. Caeca end blindly................................................................. Plesioschistorchis n. gen.

As part of this study, we obtained additional specimens of Plesio. callyodontis ( Yamaguti, 1942) n. comb. and Pleiso. haridis ( Nagaty, 1957) n. comb. from the common parrotfish, Scarus psittacus Forsskål (locally known as “Ghabban”) ( Perciformes : Scaridae ), from the northern Red Sea off southern Hurghada, Egypt, and both species are re-described below.