Plesioschistorchis callyodontis ( Yamaguti, 1942 ) 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 : 15-21

Plesioschistorchis callyodontis ( Yamaguti, 1942) n. comb.

( Figs. 1–3 )

(Syn. Schistorchis callyodontis Yamaguti, 1942 )

Host: Common parrotfish (“Ghabban”), Scarus psittacus Forsskål ( Perciformes : Scaridae ).

Locality: Northern Red Sea, off Sharm El-Naga, Makadi Bay, Southern Hurghada, Egypt (26°55.16’N, 33°56.05’E– 26°53.59’N, 33°59.49’E; depth = 0.5–2.5 m; 01/January/2012).

Site of infection: Mid-intestine.

Deposited material: BM(NH) vouchers NHMUK 2017.9.28.10–11; 2 slides / 2 specimens .

Prevalence: 2 of 8 host specimens (25% infected).

Intensity: 4 worms/host specimen.

Mean intensity: 2.00 (4/2).

Relative density/abundance: 0.50 (4/8).

Re-description: [Based on 4 mature specimens. Measurements, morphometric percentages and morphometric ratios are given in Table 2]. Body plump, elongate with almost parallel margins, maximum width either at level of junction of first and second 1/4 of body (i.e. just posterior to ventral sucker) or at midbody (i.e. just posterior to level of ovary). Anterior extremity less broadly rounded; posterior extremity more rounded. Tegument smooth. Forebody attenuated; hindbody wider than forebody, gradually narrows in posterior 1/3 of body. Pre-oral lobe short and distinct. Oral sucker rounded to subspherical, muscular, distinctly ventro-subterminal, “simple” type with no anterior circumoral lobes; mouth conspicuous, rounded, directed anteroventrally; partial U-shaped muscular sphincter half-encircling oral aperture posteroventrally. Ventral sucker pre-equatorial, situated at junction of first and second 1/5 of body, spherical to subspherical, sessile, unspecialized, equal to oral sucker in size or slightly smaller. Large mass of parenchymal cells concentrated around outer margin of ventral sucker, especially its posterior edge. Prepharynx very short, broad, either entirely outside of or retracted within posterior concavity of oral sucker. Pharynx dolioform to subquadrate, smaller than suckers, muscular, well-developed. Esophagus distinct, very short, straight, broad, slightly longer than prepharynx. Intestinal bifurcation posterior to level of midforebody, midway between pharynx and ventral sucker, separated from latter by small distance. Caeca two, simple, wider and slightly arcuate posteriorly, equal in length, pass along lateral margins of worm to terminate blindly at posterior extremity; ani absent.

Testes 11 (exceptionally 5), arranged in two zig-zag rows (6 left, 5 right), smooth, subspherical to oval, not equal in size (posteriormost testis often largest), some contiguous while others separated by small inter-testicular space, occupy area between ovary and middle of posterior 1/3 of body, well-separated from posterior end. Posttesticular region 1/5 of body length. Seminal vesicle saccate, distinct, large, clavate to pyriform, rounded proximally and tapered distally, extends anteriorly in acute angle within region between ventral sucker and ovary in anterior portion of second 1/4 of body. Pars prostatica sub-cylindrical, short, thin-walled, situated posterosinistral to ventral sucker, extends anterosinistrally around left margin of sucker to about mid-level of latter then unites with distal portion of metraterm to form hermaphroditic duct; duct itself tubular, narrow, moderate in length, continues anterosinistrally from mid-level of ventral sucker around left margin. Prostatic cells well-developed, free in parenchyma, a condensed mass distributed around pars prostatica and distal portions of seminal vesicle and metraterm. Genital pore median and immediately anterior to ventral sucker.

Ovary round, smooth, in hindbody and in posterior portion of anterior half of body, median, immediately pretesticular, separated from and anterodextral to anteriormost testis. Canalicular seminal receptacle large, oblong to retort in shape, extends obliquely between ovary and anteriormost testes. Oviduct not observed as broad posterior extent of uterus obstructs view. Mehlis’ gland cells somewhat large, dense and numerous. Laurer’s canal arises dorsally from seminal receptacle; distal portion not observed but expected to open dorsally. Vitellarium follicular; fields extend along lateral margins from level of distal portion of seminal vesicle (slightly posterior to ventral sucker) to posterior extremity, overlaps lateral margins of gonads, confluent in post-testicular region; follicles numerous, small, subspherical to oval, dorsal, ventral and lateral to caeca. Uterus pre-testicular, moderate in length and coiled, intercaecal, in anterior hindbody and restricted to area between ovary and genital pore, proximal portion overlaps anterior margin of ovary and seminal receptacle before it passes dorsal to seminal vesicle. Metraterm distinct, tubular, runs anteriorly to left of ventral sucker to join distal portion of pars prostatica. Eggs numerous, operculate, oval, moderate in size, thin-shelled, non-filamented.

Excretory vesicle I-shaped, moderately narrow, median, extends anteriorly to region near junction of second and third 1/3 of body within anterior half of testes; two primary excretory ducts (i.e. collecting tubules) extend anteriorly into forebody. Excretory pore terminal.

Figures

FIGURES 1–3. Plesioschistorchis callyodontis (Yamaguti, 1942) n. comb. (Megaperidae n. comb.: Schistorchiinae) from the common parrotfish, Scarus psittacus Forsskål (Scaridae), from the Red Sea off Egypt. 1. Adult specimen, ventral view. 2. Terminal genitalia, ventral view. 3. Elliptical eggs. Abbreviations: Ce, Cecum; EA, Excretory arm/duct; EP, Excretory pore; EV, Excretory vesicle; GP, Genital pore; HD, Hermaphroditic duct; Me, Metraterm; OS, Oral sucker; Ov, Ovary; PC, Prostatic cells; Ph, Pharynx; PM, Parenchymal mass of cells; PP, Pars prostatica; SR, Seminal receptacle; SV, Seminal vesicle; Te, Testes; Ut, Uterus; VF, Vitelline follicles; VS, Ventral sucker.