The genus includes more than 80 species, which are all parasitic on the gills of marine fish, especially groupers. Since groupers are mostly abundant in warm waters, species of Pseudorhabdosynochus are found in warm parts of the oceans, especially in coral reefs, but species have also been found in deep-sea groupers. Several species of Pseudorhabdosynochus are pathogens of maricultured groupers.
Morphology
All species of Pseudorhabdosynochus are small animals, ranging 0.3–1mm in length.
As most monogeneans, they are flat, with an anterior head bearing four oculi and head glands, a main elongate body and a posterior haptor. The digestive system includes an anterior muscular pharynx, and two lateral intestinal branches (or caeca); as in all Platyhelminthes, there is no anus. The haptor, in the posterior part of the body, is a specialized organ used to attach to the host. The haptor includes sclerotized elements, namely a ventral bar, two lateral (dorsal) bars, two ventral hooks and two dorsal hooks, and fourteen hooklets. As in most diplectanids, the haptor bears special, characteristic, structures called squamodiscs. The squamodiscs (one ventral and one dorsal) of species of Pseudorhabdosynochus are made up of numerous rodlets aligned as concentric rows. All species of the genus have two squamodiscs except Pseudorhabdosynochus sinediscusNeifar & Euzet, 2007 in which these organs are completely lacking.
Adults are hermaphroditic. The reproductive organ include a single ovary and a single testis. As in all diplectanids, the ovary (or germarium) is anterior to the testis and loops around the right intestinal caecum. Species of Pseudorhabdosynochus are characterized by a sclerotized male copulatory organ, or "quadriloculate organ", which has the shape of a bean with four internal chambers. The vagina includes a sclerotized part, which is a complex structure with several chambers and canals, generally used for the diagnosis and differentiation of species.
Etymology and nomenclatural case
The origin of the name Pseudorhabdosynochus merits an explanation. ‘Pseudo-’ (from Greek ψευδής, pseudes, "lying, false") is a prefix commonly used in creating a new scientific name for a taxon that superficially appears to be a taxon, but actually is another. The famous Japanese parasitologist Satyu Yamaguti described a ‘membranous plaque’ on the posterior region of Pseudorhabdosynochus epinepheli and created[1] the generic name Pseudorhabdosynochus in reference to the diplectanid genus Rhabdosynochus which, in his interpretation, also had lateral plaques. It has been shown later that ‘plaques’ in P. epinepheli was an erroneous interpretation of damaged specimens.[2][3] Moreover, the diagnosis of Rhabdosynochus was later modified and it is now considered that species of this genus do not have plaques.[4] Therefore, the genus name Pseudorhabdosynochus is the result of both an erroneous observation and an erroneous comparison by Satyu Yamaguti. However, it is valid according to the ICZN.[2]
Pseudorhabdosynochus is also an interesting nomenclatural case. Yamaguti described the same species twice, the first time in 1938 [5] (as Diplectanum epinepheli Yamaguti, 1938) and the second time in 1958 [1] (as Pseudorhabdosynochus epinepheli Yamaguti, 1958). In both papers, the species was described from parasites collected from the same fish species, the grouper Epinephelus akaara off Japan. Kritsky & Beverley-Burton (1986) [2] solved this case with reference to the International Code of Zoological Nomenclature. The type-species of the genus is the namePseudorhabdosynochus epinepheli Yamaguti, 1958. Pseudorhabdosynochus epinepheliYamaguti, 1958 is a junior synonym of Pseudorhabdosynochus epinepheli(Yamaguti, 1938) Kritsky & Beverley-Burton, 1986 and Pseudorhabdosynochus epinepheli (Yamaguti, 1938) Kritsky & Beverley-Burton, 1986 is the modern valid combination for Diplectanum epinepheliYamaguti, 1938. The latter species (a taxon) and the type-species of the genus (a name) are considered to correspond to the same biological taxon but have different, although valid, names. Recent re-examination of type-specimens have confirmed this interpretation. [3]
As most diplectanids,[9] species of Pseudorhabdosynochus are generally strictly species-specific, i.e. a species is found on a single species of host and no others. However, several exceptions have been reported.[10] Some species of groupers harbour a wide biodiversity of Pseudorhabdosynochus species (and sometimes other monogeneans as well). Examples are Epinephelus maculatus which has 8 distinct Pseudorhabdosynochus species,[11] and Epinephelus malabaricus which has 7 species.[12][13]
Life cycle
The life cycle of Pseudorhabdosynochus species is similar to that of other diplectanid monogeneans.[9] It is monoxenous, i.e. there is a single host, the fish. The life-cycle includes a parasitic phase, the adult worm, and two stages which are free in the environment, the egg and the larva. The adult hermaphroditic worm, which lives on the gills of fish, lays eggs in the water. The egg has an operculum. A larva develops in the egg and hatches through the operculum; the swimming larva is ciliated and called an oncomiracidium. The larva finds its host by swimming to it, first attaches to the skin and migrates to the gills, and eventually transforms itself into a young monogenean which is attached to the gill filament by its haptor. During transformation from larva to adult, the monogenean loses its cilia and produces a new tegument, a phenomenon which is considered a general characteristic of the parasitic Platyhelminthes or Neodermata.[14]
Information is available for the life-cycle of Pseudorhabdosynochus lantauensis, a parasite of the orange-spotted grouper Epinephelus coioides, at a temperature of 30°C.[15] The adult lays 10-22 eggs/day. The eggs hatch within 2–4 days. The oncomiracidium is viable for 4-8 h and should find a host within this delay. After attachment, the oncomiracidium transforms into an adult in 4–7 days. The parasite produces eggs after 7 days. The life-cycle is thus complete in 13–20 days (at 30°C).[15]
Certain species of Pseudorhabdosynochus parasitize groupers which show spawning aggregations, i.e. the adult fish gather annually at a precise location and meet other fish of their own species only once per year. It has been suggested that transmission of Pseudorhabdosynochus species occurs preferentially during these spawning aggregations, from older infected fish to younger, uninfected, fish.[16]
Pathology and control in mariculture
Species of Pseudorhabdosynochus are attached to the gills of groupers. No information is available on the pathogen effect of these parasites in wild groupers. Since the life-cycle is monoxenous and thus can be completed with a high rate of success in mariculture condition, species of Pseudorhabdosynochus can proliferate on gills of cultured groupers and become dangerous for the fish, inducing mortality.
Lists of species have been provided by Kritsky & Beverley-Burton (1986)[2] and Justine (2007). [11] The list below (about 80 species) is based on the World Register of Marine Organisms[24] with additions.
Pseudorhabdosynochus epinepheli is a diplectanid monogenean parasitic on the gills of species of groupers. It is the type species of the genus Pseudorhabdosynochus Yamaguti, 1958.
Pseudorhabdosynochus capurroi is a diplectanid monogenean parasitic on the gills of the Black grouper, Mycteroperca bonaci. It was described by Vidal-Martínez and Mendoza-Franco in 1998 and redescribed successively by Yang, Gibson and Zeng in 2005 and by Kritsky, Bakenhaster and Adams in 2015.
Pseudorhabdosynochus huitoe is a diplectanid monogenean parasitic on the gills of the highfin grouper, Epinephelus maculatus. It was described in 2007.
Pseudorhabdosynochus caledonicus is a diplectanid monogenean parasitic on the gills of the Blacktip grouper, Epinephelus fasciatus. It has been described in 2005.
Pseudorhabdosynochus cyathus is a diplectanid monogenean parasitic on the gills of the grouper Epinephelus howlandi. It has been described in 2006.
Pseudorhabdosynochus calathus is a diplectanid monogenean parasitic on the gills of the grouper Epinephelus rivulatus. It has been described in 2006.
Pseudorhabdosynochus morrhua is a diplectanid monogenean parasitic on the gills of the grouper Epinephelus morrhua. It has been described in 2008.
Pseudorhabdosynochus quadratus is a species of diplectanid monogenean that is parasitic on the gills of the white-streaked grouper Epinephelus ongus. It was described in 2011.
Laticola is a genus of monopisthocotylean monogeneans, belonging to the family Diplectanidae. All known species are parasitic on the gills of marine fish, including members of Lates (Latidae) and Epinephelus (Serranidae).
Pseudorhabdosynochus dionysos is a species of diplectanid monogenean that is parasitic on the gills of the camouflage grouper Epinephelus polyphekadion. It was described in 2011.
Pseudorhabdosynochus exoticoides is a species of diplectanid monogenean that is parasitic on the gills of the brownspotted grouper Epinephelus chlorostigma. It was described in 2010.
Pseudorhabdosynochus stigmosus is a species of diplectanid monogenean that is parasitic on the gills of the brownspotted grouper Epinephelus chlorostigma. It was described in 2010.
Pseudorhabdosynochus exoticus is a species of diplectanid monogenean that is parasitic on the gills of the blue grouper Epinephelus cyanopodus. It was described in 2008.
Laticola dae is a species of diplectanid monogenean. It is parasitic on the gills of the Highfin grouper, Epinephelus maculatus. It was described in 2006. The species is a member of the genus Laticola Yang, Kritsky, Sun, Zhang, Shi & Agrawal, 2006. More than 400 specimens of this parasite were studied for the description of the species, which was the most abundant monogenean species, representing about 50% of the specimens found on this fish.
Pseudorhabdosynochus cupatus is a species of diplectanid monogenean parasitic on the gills of groupers.
Pseudorhabdosynochus youngi is species of diplectanid monogenean parasitic on the gills of the blacktip grouper, Epinephelus fasciatus. It was described in 2009.
Pseudorhabdosynochus melanesiensis is a diplectanid monogenean parasitic on the gills of the grouper, Epinephelus merra. It was described in 1958 as Diplectanum melanesiensis then transferred to the genus Pseudorhabdosynochus by Kritsky & Beverley-Burton in 1986.
Pseudorhabdosynochus riouxi is a species of diplectanid monogenean parasitic on the gills of dusky grouper Mycteroperca marginata. It was described by Guy Oliver in 1986 as Cycloplectanum riouxi, then transferred to the genus Pseudorhabdosynochus by Santos, Buchmann & Gibson in 2000. The species has been redescribed by Chaabane et al. in 2017.
Pseudorhabdosynochus magnisquamodiscum is species of diplectanid monogenean parasitic on the gills of a fish. It was described in 1984 under the name Cycloplectanum magnisquamodiscum and later transferred to the genus Pseudorhabdosynochus.
Pseudorhabdosynochus vagampullum is a species of diplectanid monogenean parasitic on the gills of a grouper. It was described in 1969, from eight specimens, under the name Diplectanum vagampullum and transferred to the genus Pseudorhabdosynochus in 1986. The species has been redescribed several times.
References
1 2 Yamaguti, S. 1958: Studies on the helminth fauna of Japan. Part 53. Trematodes of fishes, XII. Publications of the Seto Marine Biological Laboratory, 7, 53-88. ArticlePDF
↑ Kritsky, D. C., Boeger, W. A. & Robaldo, R. B. 2001: Neotropical Monogenoidea. 38. Revision of Rhabdosynochus Mizelle and Blatz, 1941 (Polyonchoinea: Dactylogyridea: Diplectanidae), with descriptions of two new species from Brazil. Comparative Parasitology, 68, 66-75.
1 2 Yamaguti, S (1938). "Studies on the helminth fauna of Japan. Part 24. Trematodes of fishes, V". Japanese Journal of Zoology. 8: 15–74.
1 2 3 4 5 6 7 Mendoza-Franco, Edgar F.; Violante-González, Juan; Rojas Herrera, Agustín A. (2011). "Six new and one previously described species of Pseudorhabdosynochus (Monogenoidea, Diplectanidae) infecting the gills of groupers (Perciformes, Serranidae) from the Pacific coasts of Mexico and Panama". Journal of Parasitology. 97 (1): 20–35. doi:10.1645/GE-2716.1. ISSN0022-3395. PMID21348602. S2CID207251069.
1 2 3 4 5 6 7 8 9 10 Justine, Jean-Lou (2007). "Parasite biodiversity in a coral reef fish: twelve species of monogeneans on the gills of the grouper Epinephelus maculatus (Perciformes: Serranidae) off New Caledonia, with a description of eight new species of Pseudorhabdosynochus (Monogenea: Diplectanidae)". Systematic Parasitology. 66 (2): 81–129. doi:10.1007/s11230-006-9057-3. PMID16972153. S2CID7737882.
↑ Ehlers, U. (1985). Das Phylogenetische System der Plathelminthes. Stuttgart: G. Fischer.
1 2 Erazo-Pagador, G.; Cruz-Lacierda, E. R. (2010). "The morphology and life cycle of the gill monogenean (Pseudorhabdosynochus lantauensis) on orange-spotted grouper (Epinephelus coioides) cultured in the Philippines". Bulletin of the European Association of Fish Pathologists. 30: 55–64.
1 2 3 4 5 Sigura, A.; Justine, J.-L. (2008). "Monogeneans of the speckled blue grouper, Epinephelus cyanopodus (Perciformes, Serranidae), from off New Caledonia, with a description of four new species of Pseudorhabdosynochus and one new species of Laticola (Monogenea: Diplectanidae), and evidence of monogenean faunal changes according to the size of fish". Zootaxa. 1695: 1–44. doi:10.11646/zootaxa.1695.1.1.
↑ Ruangpan, L. & Tubkaew, R. (1993). Parasites of the cage cultured grouper Epinephelus malabaricus in Thailand. Paper presented at the Proceedings of Grouper Culture, Kaoseng, Songkhla, Thailand.
↑ Rückert, Sonja; Klimpel, Sven; Al-Quraishy, Saleh; Mehlhorn, Heinz; Palm, Harry W. (2008). "Transmission of fish parasites into grouper mariculture (Serranidae: Epinephelus coioides (Hamilton, 1822)) in Lampung Bay, Indonesia". Parasitology Research. 104 (3): 523–532. doi:10.1007/s00436-008-1226-7. ISSN0932-0113. PMID18855012. S2CID15956362.
1 2 Vidal-Martínez, V. M., Aguirre-Macedo, L. & Mendoza-Franco, E. F. 1997: Pseudorhabdosynochus yucatanensis sp. n. (Monogenea: Diplectanidae) from the gills of the red grouper Epinephelus morio (Pisces: Serranidae) of the Yucatan Peninsula, Mexico" Folia Parasitologica 44, 274-278. PDF
1 2 Justine, Jean-Lou (2007). "Pseudorhabdosynochus argus n. sp. (Monogenea: Diplectanidae) from Cephalopholis argus, P. minutus n. sp. and Diplectanum nanus n. sp. from C. sonnerati and other monogeneans from Cephalopholis spp. (Perciformes: Serranidae) off Australia and New Caledonia". Systematic Parasitology. 68 (3): 195–215. doi:10.1007/s11230-007-9096-4. ISSN0165-5752. PMID17896188. S2CID23506802.
1 2 Oliver, G. & Paperna, I. 1984: Diplectanidae Bychowsky, 1957 (Monogenea, Monopisthocotylea), parasites de Perciformes de Méditerranée orientale, de la mer Rouge et de l'océan Indien. Bulletin du Muséum National d'Histoire Naturelle, Paris, 4° série, 6, section A, 49-65.
↑ Justine, Jean-Lou (2005). "Species of Pseudorhabdosynochus Yamaguti, 1958 (Monogenea: Diplectanidae) from Epinephelus fasciatus and E. merra (Perciformes: Serranidae) off New Caledonia and other parts of the Indo-Pacific Ocean, with a comparison of measurements of specimens prepared using different methods, and a description of P. caledonicus n. sp". Systematic Parasitology. 62 (1): 1–37. doi:10.1007/s11230-005-5480-0. ISSN0165-5752. PMID16132868. S2CID35119181.
↑ Vidal-Martínez, V. M. & Mendoza-Franco, E. F. 1998: Pseudorhabdosynochus capurroi sp. n. (Monogenea: Diplectanidae) from the gills of Mycteroperca bonaci (Pisces: Serranidae) of the Yucatan Peninsula, Mexico" Folia Parasitologica 45, 221-224. Article PDF
↑ Zhang, J. Y., Yang, T. B. & Liu, L. (2001). [Monogeneans of Chinese marine fishes] (in Chinese). Beijing: Agriculture Press.
↑ Bu, S. S. H.; Leong, T. S.; Wong, S. Y.; Woo, Y. S. N.; Foo, R. W. T. (1999). "Three diplectanid monogeneans from marine finfish (Epinephelus spp.) in the Far East". Journal of Helminthology. 73 (4): 301–312. doi:10.1017/S0022149X99000505. S2CID86124568.
1 2 3 Schoelinck, Charlotte; Justine, Jean-Lou (2011). "Four species of Pseudorhabdosynochus (Monogenea: Diplectanidae) from the camouflage grouper Epinephelus polyphekadion (Perciformes: Serranidae) off New Caledonia". Systematic Parasitology. 79 (1): 41–61. doi:10.1007/s11230-010-9289-0. ISSN0165-5752. PMID21487947. S2CID23523617.
1 2 Justine, Jean-Lou; Henry, Émilie (2010). "Monogeneans from Epinephelus chlorostigma (Val.) (Perciformes: Serranidae) off New Caledonia, with the description of three new species of diplectanids". Systematic Parasitology. 77 (2): 81–105. doi:10.1007/s11230-010-9263-x. ISSN0165-5752. PMID20852982. S2CID36351344.
1 2 3 4 Santos, Cláudia Portes; Buchmann, Kurt; Gibson, David I. (2000). "Pseudorhabdosynochus spp. (Monogenea: Diplectanidae) from the gills of Epinephelus spp. in Brazilian waters". Systematic Parasitology. 45 (2): 145–153. doi:10.1023/A:1006232029426. ISSN0165-5752. PMID10743859. S2CID26949491.
↑ Justine, Jean-Lou (2005). "Pseudorhabdosynochus hirundineus n. sp. (Monogenea: Diplectanidae) from Variola louti (Perciformes: Serranidae) off New Caledonia". Systematic Parasitology. 62 (1): 39–45. doi:10.1007/s11230-005-5481-z. ISSN0165-5752. PMID16132869. S2CID2967245.
↑ Saengpheng, Chompunooch; Purivirojkul, Watchariya (2020-01-07). "Pseudorhabdosynochus kasetsartensis n. sp. (Monogenea: Diplectanidae) from the cloudy grouper Epinephelus erythrurus (Valenciennes) (Perciformes: Serranidae) in the lower Gulf of Thailand". Systematic Parasitology. 97 (1): 99–106. doi:10.1007/s11230-019-09899-z. ISSN0165-5752. PMID31912419. S2CID209897022.
↑ Dyer, William G.; Williams, Ernest H.; Bunkley-Williams, Lucy (1995). "Pseudorhabdosynochus kritskyi n. sp. (Monogenea: Diplectanidae) on Gag from the Gulf of Mexico". Journal of Aquatic Animal Health. 7 (4): 337–340. doi:10.1577/1548-8667(1995)007<0337:KNSDOG>2.3.CO;2. ISSN0899-7659.
↑ Beverley-Burton, Mary; Suriano, Delia Mabel (1981). "A revision of Cycloplectanum Oliver, 1968 (Monogenea: Diplectanidae) and descriptions of C.hongkongensis n.sp. and C.lantauensis n.sp. from Epinephelus spp. (Serranidae) in the South China Sea". Canadian Journal of Zoology. 59 (7): 1276–1285. doi:10.1139/z81-180. ISSN0008-4301.
↑ Aljoshkina, L. D. (1984). "[New species of the family Diplectanidae (Monogenea) in the South-West Atlantic]". Zoologicheskii Zhurnal. 63: 1253–1256.
↑ Laird, Marshall (1958). "Parasites of South Pacific fishes II. Diplectanum melanesiensis n. sp., a monogenetic trematode from Fiji and the New Hebrides". Canadian Journal of Zoology. 36 (2): 167–173. doi:10.1139/z58-017. ISSN0008-4301.
↑ Dyer, William G.; Williams, Ernest H.; Bunkley-Williams, Lucy (1994). "Pseudorhabdosynochus monaensis n. sp. (Monogenea: Diplectanidae) on Rock Hind from Mona Island, Puerto Rico". Journal of Aquatic Animal Health. 6 (1): 59–63. doi:10.1577/1548-8667(1994)006<0059:PMNSMD>2.3.CO;2. ISSN0899-7659.
1 2 Justine, Jean-Lou (2008). "Two new species of Pseudorhabdosynochus Yamaguti, 1958 (Monogenea: Diplectanidae) from the deep-sea grouper Epinephelus morrhua (Val.) (Perciformes: Serranidae) off New Caledonia". Systematic Parasitology. 71 (2): 145–158. doi:10.1007/s11230-008-9156-4. ISSN0165-5752. PMID18716902. S2CID23245863.
↑ Justine, Jean-Lou; Vignon, Matthias (2008). "Monogeneans of the grouper Epinephelus tauvina (Perciformes, Serranidae) off Moorea, French Polynesia, with a description of Pseudorhabdosynochus pai n. sp. (Monogenea: Diplectanidae)". Systematic Parasitology. 72 (2): 113–125. doi:10.1007/s11230-008-9159-1. ISSN0165-5752. PMID19115085. S2CID7679605.
↑ Schoelinck, Charlotte; Justine, Jean-Lou (2011). "Pseudorhabdosynochus quadratus n. sp. (Monogenea: Diplectanidae) from the white-streaked grouper Epinephelus ongus (Bloch) (Perciformes: Serranidae) off New Caledonia". Systematic Parasitology. 79 (1): 77–80. doi:10.1007/s11230-011-9295-x. ISSN0165-5752. PMID21487950. S2CID22318648.
↑ Yamaguti, S. (1968). Monogenetic Trematodes of Hawaiian Fishes. Honolulu: University of Hawaii Press.
↑ Oliver, Guy (1986). "Cycloplectanum riouxi n. sp., une nouvelle espèce de Diplectanidae (Monogenea, Monopisthocotylea) parasite d'Epinephelus guaza (Linnaeus, 1758) (Pisces, Serranidae)". Systematic Parasitology. 8 (4): 317–322. doi:10.1007/BF00009739. ISSN0165-5752. S2CID39530925.
↑ Yang, Tingbao; Zeng, Bijian; Gibson, David I. (2005). "Description of Pseudorhabdosynochus shenzhenensis n. sp. (Monogenea: Diplectanidae) and redescription of P. serrani Yamaguti, 1953 from Epinephelus coioides off Dapeng Bay, Shenzhen, China". Journal of Parasitology. 91 (4): 808–813. doi:10.1645/GE-518R.1. ISSN0022-3395. PMID17089747. S2CID19512689.
↑ Yang, Tingbao; Gibson, David I.; Zeng, Bijian (2005). "Pseudorhabdosynochus summanoides n. sp. (Monogenea: Diplectanidae) from Epinephelus coioides in Dapeng Bay, South China Sea, with observations on several similar species of Pseudorhabdosynochus Yamaguti, 1958". Systematic Parasitology. 62 (3): 221–239. doi:10.1007/s11230-005-5497-4. ISSN0165-5752. PMID16315082. S2CID7907556.
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