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Pelopscreadium aegyptense n. sp. (Figs. 1–4) Type-host. Yellow boxfish, Ostracion cubicus Linnaeus (Tetraodontiformes: Ostraciidae). Type-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; 26 /May/ 2012). Site of infection. Lower intestine. Type-material. BM(NH) holotype 2016.4.22.1, BM(NH) paratypes 2016.4.22.2, BM(NH) vouchers 2016.4.22.3- 10. Pevalence. 2 of 8 host specimens (25 % infected). Intensity. 13–17 worms/host specimen. Mean intensity. 15 (30 / 2). Relative density/abundance. 3.75 (30 / 8). Etymology. The species designation “ aegyptense ” refers to the geographical location where this new digenean was collected, i.e. off Egypt. Description. [Based on 18 mature specimens. Measurements, morphometric percentages and morphometric ratios are given in Table 1.] Body elongate-oval, with maximum width in middle third of body. Anterior end broadly rounded; posterior end less broadly rounded; pre-oral lobe present. Forebody gradually narrows near anterior end; remnants of cercarial eyespots often obvious in first third of forebody. Hindbody wider than forebody, gradually narrows in posterior third of body. Large internal patches of vacuolated cells form sponge-like pelops (“shoulder pads”) laterally between anterior extremity and level 2 / 3 to 3 / 4 length of forebody. Tegument densely spined anteriorly; spines short, generally scale-like, becoming less dense posterior to sponge-like pelops, sparsely distributed from posterior extent of sponge-like pelops to near posterior extremity. Distinct, narrow, welldifferentiated layer (band) of cells immediately inside anterior margin of body extends posteriorly on both sides two-thirds length of forebody. Oral sucker spherical to transversely elongate-oval, distinctly sub-terminal, somewhat embedded in parenchyma, partially covered by tegument, unspecialized with conspicuous central mouth opening. Ventral sucker sessile, spherical to ovoid, immediately pre-equatorial, occasionally equatorial, unspecialized, smaller than oral sucker. Prepharynx short, broad and either entirely outside in 89 % [n= 16] or retracted within posterior concavity of oral sucker in 11 % [n= 2] of specimens. Pharynx muscular, subspherical, narrower than oral sucker; 5 dorsal papillae (line of 3 large middle papillate projections with 1 somewhat smaller papillate projection that abuts each end of row on dorsal rim of anterior pharyngeal aperture) and 3 ventral papillate projections on ventral side of margin of aperture (like petals of flower) with 2 extensions of pharyngeal wall inserted between dorsal and ventral rows of papillae. Esophagus distinct, short, straight, longer than prepharynx. Intestinal bifurcation in posterior forebody. Ceca 2, simple, equal in length, widest just posterior to ventral sucker, somewhat arcuate, pass along lateral margins of worm to posterior end, where they abruptly terminate near body wall; ani absent. Testes 2, transversely elongate, slightly to deeply lobed, median, tandem, contiguous, in posterior third of body. Distance from ventral sucker to anterior testis relatively long. External seminal vesicle long, tubular, sinuous throughout, larger than internal seminal vesicle, reaches from posterior aspect of sinistral rim of ventral sucker or slightly dorsal to it to about level of ovary. “ Opechona - type ” cirrus-sac (Bray 2005; Bray & Cribb 2012), large, claviform, sinistral to mid-line, extends posteriorly from short distance anterior to ventral sucker to short distance posterior to it, encloses ejaculatory duct, pars prostatica and internal seminal vesicle. Internal seminal vesicle oval, less extensive than pars prostatica, in posterior region of cirrus-sac. Pars prostatica conspicuous, thick-walled, almost straight, elongate-oval, much longer than ejaculatory duct, lined with anuclear cell-like bodies (anuclear blebs). Ejaculatory duct short, distinct. Genital atrium distinct. Genital pore immediately post-bifurcal, ventrosubmedian, sinistral, in forebody, overlaps left cecum or opens just medial to it. ......continued on the next page ......continued on the next page n = Sample size. NG = Not given in original description. 1 Calculated from measurements given in the original description. 2 Entirely within posterior concavity of oral sucker. 3 Calculated from Fig. 18 of the original description. 4 Calculated from Fig. 20 of the original description. 5 Based on 8 specimens exclusive of the holotype where the terminal genitalia was clearest. Ovary immediately pre-testicular, sometimes contiguous with anterior testis, dextral to nearly medial, multilobed, consists of about 9–16 separate sub-globular follicles. Seminal receptacle canalicular, large, elongate-oval, sinistral to ovary, located beside or ventral to sinistral rim of anterior testis, narrows anteriorly to form Laurer’s canal which winds back posteriorly along sinistral side of seminal receptacle and opens dorsally at level of anterior third of seminal receptacle. Uterus pre-testicular, tubular, intercecal, mainly in anterior hindbody, begins at level of ovary and passes antero-sinistrally and laterally to ventral sucker, may overlap anterior margin of ovary and posterior margin of ventral sucker. Metraterm distinct, thick-walled, lined by cells with large nuclei (i.e. “muscular” wall of Bray & Cribb 1998), extends posteriorly about 3 / 4 length of cirrus-sac, enters genital atrium from left. Vitellarium follicular; fields extend along lateral margins from near level of intestinal bifurcation to posterior extremity, completely confluent in forebody and in post-testicular region, often encroaches into immediate pre-ovarian space. Follicles numerous, subspherical to elongate-oval or irregular in shape, both ventral and lateral to ceca but not dorsal. Eggs relatively numerous, oval, small, operculate, thin-shelled. Excretory vesicle I-shaped, wide, appears to reach almost to level of intestinal bifurcation. Excretory pore terminal to dorsally subterminal. Remarks. The new species has an “ Opechona - type ” cirrus-sac and is placed in the Lepocreadiidae based on the reorganization of the Lepocreadioidea by Bray & Cribb (2012). In addition, the presence of a genital pore that is ventral and submedian, two testes, sponge-like lateral patches (pelops) in the anterior portion of the forebody instead of the lateral margins in the anterior portion of the body forming an incomplete scoop (i.e. not joined posteriorly), and ceca that extend close to the posterior body wall place this new species in Pelopscreadium n. gen.; however, there are distinct differences between the new species and the type-species of the new genus, P. spongiosum n. comb. (syn. Bianium spongiosum). Pelopscreadium spongiosum resembles P. aegyptense n. sp. in lacking a scoop and instead possessing large, internal patches of voluminous vacuolated cells which form symmetrical, sponge-like, lateral pelops in the forebody of the worm in the region between the anterior margin of the oral sucker and about the level of the intestinal bifurcation (Bray & Cribb 1998). Along with the sponge-like, lateral pelops both species are also somewhat similar in overall appearance, egg size (60–63 × 40–45 µm in P. spongiosum vs 56–65 × 38–45 µm in P. aegyptense), sucker ratio (1: 0.73–1: 0.74 vs 1: 0.59–1: 0.94), possessing a sinistrally submedian and post-bifurcal genital pore, and both have a similar vitelline distribution (Table 1; Bray & Cribb 1998). Pelopscreadium aegyptense and P. spongiosum differ in a number of features, the most striking of which is the extent and appearance of the external seminal vesicle and the distribution of the contents of the cirrus-sac. Within the cirrussac, the pars prostatica of P. spongiosum was described as “oval, vesicular”; whereas, the pars prostatica of P. aegyptense is more elongate with a conspicuously longer longitudinal axis (about 63 vs 89–165 µm) and it generally occupies a greater portion of the cirrus-sac (23 % vs 26–41 % of the cirrus-sac length, respectively). The external seminal vesicle of P. spongiosum was described by Bray & Cribb (1998, figs. 18 & 20) as “saccular, reaching to about level of ovary”, and it is illustrated as a simple, moderately-wide, oblong pouch (about 150 µm long—see Table 1). However, the external seminal vesicle of P. aegyptense is tubular, considerably more elongate and sinuous, and longer than the cirrus-sac (485–540 compared to 150 µm). Additionally, the cirrus-sac of P. aegyptense ranges from terminating at the level of the posterior margin of the ventral sucker to surpassing the ventral sucker a relatively short distance into the hindbody; whereas, in P. spongiosum it extends some distance into the hindbody (about half the length of the distance between the ventral sucker and the ovary). Another difference between these two species is the appearance of the testes. In P. aegyptense the testes are consistently irregular in shape and slightly to deeply lobed, but in P. spongiosum they are subglobular and entire (smooth) (Bray & Cribb 1998, fig. 18). Although any differences in testicular shape (entire vs lobed) may simply reflect the potentially “plastic” nature of this morphological feature within many groups of digeneans (e.g. see Dronen et al. 2014, for a discussion of the difficulties in using testicular shape as a distinguishing taxonomic feature for species within the opecoelid genus Neolebouria Gibson, 1976) and on its own may not be a “strong enough character” to distinguish species, it is likely that in this particular instance, this feature may be more taxonomically (phylogenetically) informative than in some other digenean groups. We also observed that although the body lengths of P. aegyptense and P. spongiosum overlap (Table 1), specimens of P. aegyptense tend to be larger overall (1,352–1,412 × 438–489 vs 1,160–2,642 × 775–1,356 µm). The extent of the metraterm relative to body length differed between these two species (about 75 µm, or 5 % the length of the body in P. spongiosum vs 180–335 µm or 7–16 % in P. aegyptense), and while both species parasitize the yellow boxfish, O. cubicus, their geographical localities are considerably distant (Australia vs Red Sea off Egypt).

Genus Pelopscreadium n. gen. Type-species: Pelopscreadium spongiosum (Bray & Cribb, 1998) n. comb. Syn. Bianium spongiosum Bray & Cribb, 1998 Etymology. The generic designation is derived from the name of the Greek god, Pelops, the grand-son of Zeus, who had his shoulder eaten accidentally by Demetrius; thus, “Pelops” refers to the empty (= eaten) vacuolated cells composing the sponge-like lateral patches/pads located laterally in the forebody (i.e. at the “shoulders”) of members of the new genus and the suffix “creadium” broadly refers to the affinities of the new genus to other members of the Lepocreadiinae. Diagnosis. Body spinose, elongate-oval; maximum breadth at or posterior to level of ventral sucker. Forebody about a third of body length. No scoop present, but large internal patches of vacuolated cells form sponge-like patches (i.e. “shoulder pads”) termed “pelops” (“pelop” sing.) laterally in forebody from anterior extremity to about 1 / 3 body length. Pre-oral lobe present, often inconspicuous. Oral sucker spherical to transversely elongateoval, subterminal. Ventral sucker spherical, pre-equatorial, smaller than oral sucker. Prepharynx short. Pharynx transversely oval, well developed, papillate around anterior opening. Esophagus short. Intestinal bifurcation in posterior part of forebody. Ceca two, long, terminating short of posterior extremity near body wall; no ani present. Testes two, smooth to lobed, tandem, contiguous or nearly so, post-ovarian, in posterior third of body. Posttesticular region short. External seminal vesicle tubular or sac-like. Cirrus-sac large, claviform, extends some distance into hindbody. Internal seminal vesicle oval, in posterior region of cirrus-sac. Pars prostatica elongate oval to oblong, distinct, lined with anuclear blebs (distal extremities of prostatic cells). Ejaculatory duct short to long, well developed, usually folded to some extent. Genital atrium distinct. Genital pore ventro-submedian in forebody. Ovary immediately pre-testicular, sometimes contiguous with anterior testis, dextral to almost medial, composed of multi-lobed acini. Seminal receptacle oval to elongate-oval, sinistral to ovary. Laurer’s canal opens on dorsal surface about level of anterior end of seminal receptacle. Uterus pre-testicular, intercecal. Metraterm distinct, with somewhat thickened wall coated on outside with cells containing large nuclei. Vitellarium follicular; fields extend from level of intestinal bifurcation to posterior extremity, confluent in forebody and in post-testicular region; follicles present laterally but not dorsal to ceca. Eggs relatively numerous, operculate, oval. Excretory vesicle Ishaped, wide, extends almost to level of intestinal bifurcation. Excretory pore terminal to slightly subterminal and dorsal. In intestine of marine teleosts (mainly Tetraodontiformes) in tropical to subtropical waters. Remarks. As many as 26 marine species have been assigned at one time or another to Bianium as defined by Stunkard (1931), Yamaguti (1971), Bray et al. (1996) and Bray (2005). The most recent taxonomic structuring of Bianium is that of Gibson (2015), who lists nine species in the genus. One of the species acknowledged by Gibson (2015), B. spongiosum, does not conform to Bianium and does not key out to any known species in the genus (see Bray et al. 1996). As Bray & Cribb (1998, p. 143, 145) noted in their discussion on B. spongiosum, “It is far from certain into which genus this species is best placed. The nature of the termination of the ceca, the follicular ovary, the papillate pharynx and the host all point to the fact that this form is close to the diploproctodaeine genera Bianium, Diploproctodaeum and Diploproctodaeoides. It differs from these; however, in lacking any evidence of an anterior ‘scoop’ or lateral flaps … In B. spongiosum no evidence for a scoop is seen, but laterally in the forebody there are distinct sponge-like lateral patches, which appear to be made up of large vacuolated cells. B. spongiosum does not key readily to a known diploproctodaeine genus in Bray et al. (1996), but it clearly does not have a complete scoop, so we have considered Bianium to be the best current repository”. In addition, Bray & Cribb (1998) pointed out that B. spongiosum could be distinguished from other species of Bianium in the key of Sey (1995, p. 19) due to the presence of its sponge-like shoulder pads. We are only aware of B. spongiosum and the new species described herein possessing these unique spongiform pelops, in the anterolateral forebody. Bianium spongiosum is herein assigned to Pelopscreadium n. gen. as the type-species, Pelopscreadium spongiosum (Bray & Cribb, 1998) n. comb. One member of Lobatocreadium Madhavi, 1972, Lobatocreadium ryukyuense Machida & Kuramochi, 1999, has a somewhat similar general morphology (body shape, disposition of testes in the hindbody, acinous ovary, anterior wave-like projections on the pharynx or papillate projections, lack of ani, and a similar placement of the genital pore) to P. spongiosum and the new species described herein; however, like the other members of Lobatocreadium, it lacks the large internal patches of vacuolated cells that form the “sponge-like pads” laterally in the forebody.