Progyliauchen magnacetabulum sp. n.

(Fig. 2)

Type- host: S. luridus Rüppel (Teleostei, Siganidae).

Site: Lower intestine.

Type- locality: Red Sea off the coast of Rabigh (between 22°49′N and 22°54′N), Saudi Arabia. Prevalence: 12/50 fishes examined; 24%.

Type- material: Holotype and paratypes are deposited in the Natural History Museum, London, Reg. nos. 2011.8.2.1 and 2011.8.2.2–10.

Description (Based on 14 fully gravid specimens): Body fleshy, robust, tapered anteriorly, elongate to pyriform, 1,980 –3,200 (2,590) in length, 610–950 (780) in maximum width at its middle. Excretory papilla absent. Tegument unspined. Oral sucker absent. Ventral sucker large, spherical, 495–753 (624) in diameter, in middle of posterior half of body, well separated from posterior extremity. Pharynx elongate, 161–255 × 121–191 (208 × 156). Oesophagus very long, relatively narrow, highly coiled, with 2–3 loops, longer than body length, surrounded by glandular cells along most of its length. Oesophageal bulb round, large, 198–295 × 229–323 (246 × 276). Intestinal bifurcation at beginning of middle third of body; caeca simple, wide, extend into middle third of body. Testes 2, oval, symmetrical, dorsal to ventral sucker, sub-equal, 241–383 × 177–281 (312 × 229). Cirrus sac short, claviform, mainly intercaecal, 251–383 (317) in length, 148–230 (189) wide at its base, contains tubular seminal vesicle (partly external to cirrus sac), well- developed prostatic complex and relatively short ejaculatory duct; prostatic cells extend outside the cirrus sac to cover external part of seminal vesicle. Genital pore median, directly posterior to intestinal bifurcation. Ovary tetra- lobed, median, anterior to ventral sucker or between caecal extremities. Seminal receptacle oval, submedian, between ventral sucker and left caecum. Mehlis’ gland well developed. Insemination chamber located between ovary and oötype. Laurer’s canal opens on dorsal surface at level of ventral sucker. Uterus short, winding between ovary, cirrus sac and left caeum. Eggs thin-shelled, yellowish, 68–80 × 42–54 (74 × 48). Vitelline follicles relatively small, irregular, numerous, extend along caeca for almost their entire length. Transverse vitelline collecting ducts coming from vitelline follicles of each side open into small spherical vitelline reservoir dorsal to anterior border of ventral sucker. Excretory vesicle claviform, extends anteriorly to near ventral sucker; excretory pore postero- terminal.

Comment – Morphologically,the above description of P. magnacetabulum sp. n. agrees well with the concept of Progyliauchen Shalaby et Hassanine 1997, which is to date still endemic to the Siganus spp. in the Red Sea. Although, P. magnacetabulum sp. n. and P. sigani (previously, the only species of the genus) are from closely related, sympatric hosts of a similar size, the new species clearly differs in some specific features:

− The ventral sucker is spherical, large and stout (495–753 μm in diameter), but in P. sigani this sucker is transversely elongate and much smaller (188–293 × 245–372 μm).

− The oesophagus is very long, highly coiled (with 2–3 loops) and longer than the total body length if straightened, but in P. sigani the oesophagus slightly convoluted into lateral folds and much shorter (about 55% of the total body length).

− The oesophageal bulb is large (198–295 × 229–323 μm), but in P. sigani, the bulb is much smaller (130–172 μm in diameter).

− The seminal vesicle is tubular, but in P. sigani it is constricted into three parts.

In view of these differences, the present species is considered to be new to science.

Etymology: The specific name “ magnacetabulum ” of the new species refers to the large ventral sucker of the new species.