Three new species of Pseudorhabdosynochus (Monogenea, Diplectanidae) from several species of Cephalopholis and Epinephelus (Perciformes, Serranidae) from Thailand Author Saengpheng, Chompunooch Animal Systematics and Ecology Speciality Research Unit (ASESRU), Department of Zoology, Faculty of Science, Kasetsart University, 50 Ngam Wong Wan Road, Chatuchak, Bangkok 10900, Thailand Author Purivirojkul, Watchariya Animal Systematics and Ecology Speciality Research Unit (ASESRU), Department of Zoology, Faculty of Science, Kasetsart University, 50 Ngam Wong Wan Road, Chatuchak, Bangkok 10900, Thailand & Biodiversity Center Kasetsart University (BDCKU), Bangkok 10900, Thailand text Parasite 2022 Paris, France 2022-10-25 29 48 1 14 http://dx.doi.org/10.1051/parasite/2022049 journal article 10.1051/parasite/2022049 1776-1042 PMC9595041 36282090 12524483 E369EE63-2DDB-40A8-9F3D-74CBE815B46E Pseudorhabdosynochus suratthaniensis n. sp. urn:lsid:zoobank.org:act: 69811A09-7C5C-4D38-B2CA-72D77973425C Type-host : Cephalopholis argus (Bloch & Schneider) ( Perciformes , Serranidae ). Type-locality : Surat Thani Province , the lower Gulf of 0 00 0 00 Thailand , Southern Thailand (9°49 10.1 N 99°55 31.1 E), June 2019 . Type-material : Holotype , ZRC .PLA.1115; 2 paratypes , ZRC .PLA.1116-17; 2 paratypes , THNHM-Iv-19363-64; 15 paratypes , ZMKU-PM-002039-53. Site in host : Gills. Infection indices : Prevalence 100% ( one specimen examined and infected); 36 helminth specimens on the single grouper examined. Etymology : The species name “ suratthaniensis ” is treated as an adjective and was derived from the name of the province “ Surat Thani ”, where the host fish Cephalopholis argus was collected. Description ( Figs. 1 and 2 ) [Based on 20 specimens ]. Body (including haptor) 759 long (619–977, n = 20); maximum width 169 (121–216, n = 20). Tegument smooth. Anterior region with 3 pairs of lateral head organs and 2 pairs of eye-spots; anterior pair smaller than posterior pair. Pharynx median, spherical, 45 (32–54, n = 20) × 45 (30–54, n = 20). Esophagus absent. Intestinal bifurcation immediately follows pharynx. Haptor differentiated from rest of body, 222 wide (177–277, n = 20), with 2 similar squamodiscs, 2 pairs of lateral hamuli, 3 bars, and 14 marginal hooklets. Dorsal and ventral squamodiscs round-shaped, made up of rows of rodlets, 1–2 central rows oval and closed. Dorsal squamodisc 53 long (41–64, n = 20), 55 wide (40–67, n = 20), with 9–11 rows of rodlets, of which the 1–2 innermost rows form closed ovals. Ventral squamodisc 59 long (47–73, n = 20), 57 wide (41–69, n = 20), with 8–11 rows of rodlets, of which the 1–2 innermost rows form closed ovals. Ventral hamulus with distinct guard and expanded deep root, elongated shaft slightly arched and recurved toward the tip, outer length 49 (44–53, n = 20), inner length 43 (39–47, n = 20). Dorsal hamulus with indistinct guard and expanded deep root, elongated straight shaft and recurved toward the tip, outer length 42 (40–46, n = 20), inner length 27 (25–31, n = 20). Dorsal (lateral) bar straight, with flattened medial extremity and cylindrical lateral extremity, 69 long (56–72, n = 20), 19 wide (16–22, n = 20). Ventral bar 93 long (85–100, n = 20), 18 wide (15–21, n = 20), with constricted median portion, pointed ends and visible groove that extends to both thin extremities. Male quadriloculate organ divided into 4 chambers, inner length 73 (65–84, n = 20), fourth chamber ends in sclerotized cone, 19 long (14–22, n = 20), prolonged by sclerotized tube, 19 long (16–23, n = 20), end of tube prolonged by filament of variable length. Testis subspherical, intercecal. Ovary pretesticular, encircles right intestinal cecum. Vitelline follicles lateral, coextensive with intestinal ceca and confluent in large zone posterior to testis and terminate anterior to peduncle, leaving free space around squamodiscs. Egg not seen. Figure 1. Pseudorhabdosynochus suratthaniensis n. sp. from Cephalopholis argus in the lower Gulf of Thailand. (A) COMPOSITE drawing (mainly from holotype), dorsal view. (B) Male quadriloculate organ, dorsal view. (C) Sclerotized vagina, dorsal view. (D) Ventral hamulus. (E) Dorsal hamulus. (F) Ventral bar. (G) Dorsal (lateral) bar. (H) Ventral squamodisc. (I) Dorsal squamodisc. (J) Hooklet. Scale-bars: (A) 200 µm; (B)–(J) 50 µm. Figure 2. Variations (A)–(F) of the sclerotized vagina of Pseudorhabdosynochus suratthaniensis n. sp. from Cephalopholis argus in the lower Gulf of Thailand. Abbreviations: Tr – trumpet, Ca1 – primary canal, Ch1 – primary chamber, Ca2 – secondary canal. Scale-bar: 50 µm. Sclerotized vagina with a complex structure, aspect changes slightly according to specimen and orientation ( Figs. 2A–2F ). Sclerotized vagina comprises anterior trumpet, followed by primary canal, primary chamber and secondary canal; trumpet in continuity with primary canal short, straight, or curved ( Figs. 2A and 2D ), heavily sclerotized and widens into single large and thick-walled primary chamber; secondary canal connected to primary chamber around base of vagina. Total length of sclerotized vagina (measured from distal extremity of trumpet to base of vagina) 40 (36–45, n = 20), length variable because of variation in curvature of primary canal. Primary chamber subspherical 19 long (15–23, n = 20), 17 wide (16–20, n = 20). Differential diagnosis Pseudorhabdosynochus suratthaniensis n. sp. is easily distinguished from other species of Pseudorhabdosynochus by the structure of its sclerotized vagina and the number of rows of rodlets in each of its squamodiscs. Another Pseudorhabdosynochus species that has a vaginal structure similar to that of P. suratthaniensis n. sp. is P. urceolus from C. panamensis from Taboga Island in Panama . The general structure of the sclerotized vagina appeared to be similar to that of the P. suratthaniensis n. sp. Pseudorhabdosynochus urceolus can be distinguished by the following characteristics: the size of its sclerotized vagina (29 versus 40 µm in P. suratthaniensis n. sp. ); the morphology of its sclerotized vagina, with a bell-shaped opening that is not in P. suratthaniensis n. sp; and its chamber structure, with a small hollow structure on its margin that is not in P. suratthaniensis n. sp. In addition, the squamodiscs of P. urceolus have numerous rows of rodlets, that is, 14–15 rows of rodlets and a 0–1 innermost row that form complete concentric rings; but the squamodiscs of P. suratthaniensis n. sp. have 8–11 rows of rodlets and 1–2 innermost rows that form closed ovals [ 26 ]. Pseudorhabdosynochus bouaini Neifar & Euzet, 2007 from E. costae (Steindachner) out of Sfax , Tunisia has a sclerotized vagina similar to that of P . suratthaniensis n. sp. It is characterized by an anterior trumpet, followed by a short and heavily sclerotized primary canal progressively in the heavy primary chamber. However, the distal part of the primary chamber has two small sclerotized protuberances in P. bouaini (which are not in P . suratthaniensis n. sp) [ 27 ].