A new species of diplectanid (Monogenoidea) from Paranthias colonus (Perciformes, Serranidae) off Peru

Pseudorhabdosynochus jeanloui n. sp. (Monogenoidea, Diplectanidae) is described from specimens collected from the gills of the Pacific creolefish, Paranthias colonus (Perciformes, Serranidae) from a fish market in Chorrillos, Lima, Peru. The new species is differentiated from other members of the genus by the structure of its sclerotized vagina, which has two spherical chambers of similar diameter. This is the first Pseudorhabdosynochus species described from the Pacific coast of America, the third species of the genus reported from South America and the first described from a member of Paranthias.


Introduction
Pseudorhabdosynochus Yamaguti, 1958 has a very complex nomenclatural history, which was elucidated by Kritsky & Beverley Burton [14] and further confirmed by Justine [8]. Domingues & Boeger [2], in a revision of the family, enlisted 52 valid species from Pseudorhabdosynochus. After this date, 25 more species were described. The species of Pseudorhabdosynochus mostly parasitize fish belonging to Epinephelus and have been described from different regions of the world [1, 2, 6-12, 17, 19-23].
Infections of Pseudorhabdosynochus species in captive fish populations can cause substantial economic losses to the fishing industry [24]. The accurate identification of members of Pseudorhabdosynochus to species is central in studying transmission patterns and is important for control of the diseases they cause, particularly given that there are currently no effective treatment strategies for these diseases [15].
During examination on fish from a market in Chorrillos, Lima, Peru, a member of Pseudorhabdosynochus was found parasitizing Paranthias colonus (Valenciennes, 1846) (Perciformes, Serranidae), which represents a new species for the genus.

Material and methods
Two specimens of Paranthias colonus (total length 31-35 cm, weight 450-500 g) were obtained from a market in Chorrillos, Lima, Peru in November 2010. The gills were removed and placed in vials containing 1:4000 formalin solution. After 1 h, the vials were vigorously shaken and fixed in ethanol 70°GL. In the laboratory, the parasites were collected with the aid of a stereoscopic microscope and stored. Some specimens were mounted unstained in Hoyer's medium [3] for study of the sclerotized parts and others were stained with Langeron's carmine [13], cleared in beechwood creosote and mounted in Canada balsam as permanent slides. All specimens were observed and photographed in a Zeiss Axioskop brightfield microscope, equipped with a millimeter ocular, differential interference contrast (DIC) optics, and a Sony MPEGEX  digital camera. The specimens were drawn using an Olympus BX 41 brightfield microscope equipped with a drawing tube. All measurements are in micrometers; the mean is followed by the range in parentheses and the number of specimens measured when more than two. Type-specimens are deposited in the Helminthological Collection of Instituto Oswaldo Cruz (CHIOC), Rio de Janeiro, Brazil and Muséum National d'Histoire Naturelle, Paris, France (MNHN).
Specimens used for scanning electron microscopy (SEM) were fixed in 70% alcohol, washed in 0.1 M cacodylate buffer pH 7.2 and postfixed in a solution containing 1% osmium tetroxide and 0.8% potassium ferricyanide pH 7.2 for 1 h. Subsequently, they were dehydrated through a graded ethanol series, dried by means of the critical point method with CO 2 and sputter-coated with gold; they were examined in the Plataforma de Microscopia Eletrônica Rudolf Barth (IOC-Fiocruz) using a JEOL JSM-6390 LV scanning electron microscope at an accelerating voltage of 30 kV.  Body 781 (600-930; n = 7) long by 213 (105-300; n = 7) wide. Tegument scaly, posterior region with scales on ventral and dorsal surfaces from squamodiscs to level of anterior part of testis. Anterior region with three pairs of lateral head organs; two groups of cephalic glands lateral to pharynx, both with numerous ducts leading to head organs. Two pairs of eye spots; anterior pair slightly smaller than posterior one. Pharynx spherical 51 (43-55; n = 5) · 50 (43-55; n = 5). Esophagus very short, intestinal bifurcation immediately follows pharynx.
Haptor differentiated from the rest of the body, expanded laterally, width 158 (135-185; n = 9), provided with two similar squamodiscs, two pairs of anchors and 14 hooks. Testes sub-spherical, intercaecal. Vas deferens emerges from antero-sinistral part of testis, enlarges forming seminal vesicle (located in middle region of body), forms bent, transforms in duct which loops, then directs forward, enlarges distally as a deferent posterior vesicle, then connects with quadriloculate male copulatory organ. Prostatic reservoir conspicuous, with visible transverse muscular fibers, connects with quadriloculate organ. Prostatic glands medio-dextral, converge at the base of prostatic reservoir.
Sclerotized vagina with conspicuous trumpet, followed by primary canal and two spherical chambers located along canal. Trumpet wide, diameter larger than that of primary canal. Primary canal with thin wall and constriction at mid-length. Primary chamber located at posterior extremity of primary canal, spherical, with regular thin wall. Secondary canal (communication between primary chamber and secondary chamber) very short, reduced to thin perforation in width of wall of two adjacent chambers. Secondary chamber spherical, with regular thin wall, smaller than primary chamber and generally posterior to it. Unsclerotized canal from sclerotized vagina to ootype connected to secondary chamber. Total length of sclerotized vagina 55 (47-63; n = 10), primary chamber external diameter 22 (20)(21)(22)(23)(24)(25); n = 10), secondary chamber external diameter 18 (15-21; n = 10). Only two eggs observed, length 52-62, width 42.
By scanning electron microscopy, rodlets of squamodiscs can be observed as semi-circular scales.

Discussion
Pseudorhabdosynochus is unique among Diplectanidae by having a quadriloculate male copulatory organ. The genus is also characterized by a sclerotized vagina, which is the key structure for identifying species of Pseudorhabdosynochus. By these characteristics, the new species is easily accommodated to the genus [18].
Pseudorhabdosynochus jeanloui n. sp. can be distinguished from others in the genus by the morphology of the sclerotized vagina, composed of a robust elongate trumpet and two spherical chambers, with the primary chamber larger than the secondary. As in P. jeanloui n. sp., several species of the genus present a vagina with two chambers and the secondary chamber smaller than the primary, including P. epinepheli (Yamaguti, 1938) Sigura, Chauvet & Justine, 2007. Pseudorhabdosynochus jeanloui n. sp. differs from all of these species by the measurements of the total length and by the proportion of the chambers, which are significantly larger [5,7,11,20,22,25].
A species of Pseudorhabdosynochus has recently been reported [16] from the same host off Peru, but not described, and probably represents the same species as the one described here.