Monocotylids (Monogenoidea) infecting elasmobranchs in Moreton Bay,Queensland, Australia,with descriptions of Calicotyle cutmorei n. sp. (Calicotylinae) and Dendromonocotyle raiae n. sp. (Monocotylinae)

Eighteen monocotylid species were collected from elasmobranchs during surveys of the parasites of fishes of Moreton Bay, Queensland, Australia. Two new species, Calicotyle cutmorei n. sp. (Calicotylinae) from Carcharhinus sorrah (Valenciennes) (Carcharhiniformes) and Dendromonocotyle raiae n. sp. (Monocotylinae) from Hemitrygon fluviorum (Ogilby) and Neotrygon trigonoides (Castelnau) (both Myliobatiformes) are described and illustrated. Six new faunal records for Moreton Bay are reported: Thaumatocotyle australensis Beverley-Burton & Williams, 1989 (Merizocotylinae) from Maculabatis toshi (Whitley) (Myliobatiformes); Monocotyle corali Chisholm, 1998 (Monocotylinae) from Pastinachus ater (Macleay) (Myliobatiformes); Neoheterocotyle rhynchobatis (Tripathi, 1959) Chisholm, 1994 (Heterocotylinae) from Glaucostegus typus (Anonymous [Bennett]) and Aptychotrema rostrata (Shaw) (both Rhinopristiformes); and Decacotyle elpora Marie & Justine, 2005 (Decacotylinae), Dendromonocotyle torosa Chisholm & Whittington, 2004 (Monocotylinae), and Clemacotyle australis Young, 1967 (Monocotylinae) from Aetobatus ocellatus (Kuhl) (Myliobatiformes). Maculabatis toshi is a new host record for T. australensis, and A. rostrata is a new host record for N. rhynchobatis. Ten species previously recorded from Moreton Bay were collected: Monocotyle caseyae Chisholm & Whittington, 2005 (Monocotylinae) and Heterocotyle whittingtoni Chisholm & Kritsky, 2020 (Heterocotylinae) from M. toshi; Monocotyle sp. A of Chisholm (1998a) (Monocotylinae) from H. fluviorum; Dendromonocotyle kuhlii Young, 1967 and Monocotyle kuhlii Young, 1967 (both Monocotylinae) from N. trigonoides; Thaumatocotyle cf. pseudodasybatis Hargis, 1955 (Merizocotylinae), Empruthotrema kearni Whittington, 1990 (Merizocotylinae) and Decacotyle octona Young, 1967 (Decacotylinae) from A. ocellatus; and Mycteronastes icopae (Beverley-Burton & Williams, 1989) Kearn & Beverley-Burton, 1990 (Merizocotylinae) and Troglocephalus rhinobatidis Young, 1967 (Dasybatotreminae) from G. typus.

     

Euzetia occultum n. g., n. sp. (Euzetiinae n. subf.), a monocotylid monogenean from the gills of Rhinoptera neglecta (Rhinopteridae) from Moreton Bay,Queensland, Australia

Euzetia occultum n. g., n. sp. (Monogenea: Monocotylidae) is described from the gills of the Australian cownose ray Rhinoptera neglecta Ogilby collected in Moreton Bay, Queensland, Australia. Euzetia has one central and ten peripheral loculi, which is similar to species in Decacotyle Young, 1967. However Euzetia is distinguished from other genera in the family by the presence of an additional loculus on either side of the central loculus. Because Euzetia does not fit into any of the six existing subfamilies in the Monocotylidae Taschenberg, 1879, as currently recognised, we propose the Euzetiinae n. subf. to accommodate the new genus. Euzetia occultum is described and illustrated fully. This is the first published record of a monocotylid from a species of Rhinoptera Cuvier.     

<Emphasis Type="Italic">Empruthotrema longipenis</Emphasis> n. sp. (Monogenoidea: Monocotylidae: Merizocotylinae) from the olfactory sacs of the smooth butterfly ray <Emphasis Type="Italic">Gymnura micrura</Emphasis> (Bloch &amp; Schneider) (Myliobatiformes: Gymnuridae) in the Gulf of Mexico

A new species of Empruthotrema Johnston & Tiegs, 1922 is described based on specimens collected from the olfactory sacs of smooth butterfly rays Gymnura micrura (Bloch & Schneider) captured in Mobile Bay (northcentral Gulf of Mexico), Alabama, USA. Empruthotrema longipenis n. sp. is most similar to the type-species Empruthotrema raiae (MacCallum, 1916) Johnston & Tiegs, 1922 by having 12 marginal and two interhamular loculi with members of haptoral hook pair 1 located midway along the periphery of each interhamular loculus and those of hook pair 2 located at the marginal termini of the bilateral septa flanking the interhamular loculi. Empruthotrema longipenis n. sp. differs from E. raiae by having a much longer male copulatory organ and from its remaining congeners by the sinistral and extracecal ejaculatory bulb flanking the pharynx, the number of interhamular and marginal septa, and the distribution of hook pairs 1 and 2 along the haptoral margin. This is the first report of a monocotylid from the smooth butterfly ray and from Mobile Bay. The diversity of haptoral morphotypes among the currently accepted species of Empruthotrema is detailed and discussed in the context of monophyly of the genus.     

Two new species of Anchylodiscus Johnston & Tiegs, 1922 (Monogenea) from Plotosus canius (Plotosidae)

Two new species of Anchylodiscus Johnston & Tiegs, 1922, A. malayensis n. sp. and A. liewi n. sp., were obtained from the gills and the dendritic (or arborescent) organ of Plotosus canius, respectively. The two new species have two seminal vesicles; the seminal vesicle nearer the testis is a distension of the vas deferens, while the distal one is similar to the blind seminal vesicle of the majority of freshwater ancylodiscoidines. The blind seminal vesicle suggests that Anchylodiscus should be placed in the subfamily Ancylodiscoidinae.     

海南岛海水鱼类寄生海盘虫属一新种及两新纪录(单殖亚纲,锚首虫科)

首次报道了南海镰鱼Zandus cormdus（Linbacus）（采自海南岛三亚市）鳃上寄生单殖吸虫,锚首虫科Anctyrocephalidae Bychowsky ＆ Nagibina 1978,海盘虫属Haliotrema Johnston ＆ Tiegs,1922中的1新种及2新纪录种。而且,镰鱼为管阴海盘虫H．tubulovagina Yamaguti,1968和丹姆斯特海盘虫H．dempsteri（Mizele ＆ Price,1964）Young,1968的宿主新记录。文中量度微米（μm）,模式标本保存于湖南文理学院生命科学系。镰茎海盘虫,新种Haliotrema sichlocirrus sp.nov（图1～5） 宿主：镰鱼Zandus cormudus（Linnacus）。 寄生部位：鳃丝。海南三亚,2004-03—16。 比较小型的锚首虫,虫体长337～405,宽67～80。背中央大钩全长35～37,钩基长29—31,钩尖长7～10,内突长11～14,外突长4～5;腹中央大钩全长35～37,钩基长30～33,钩尖长9～12,内突长8～10,外突长3～5。背联结片中部较平直,亚中部向前稍隆起,两端向后微弯,大小（5～6）×（60～66）;腹联结片呈弧形弯曲,两端较中部宽阔,大小（6～8）×（55～63）。交接器由阴茎、基座和支持器组成。阴茎呈短管状、较直,管长19～22,基径7～11;基部有一钟形基座,高10～13,底径10～13;支持器长45～53（据弯度）,基端呈细条状,宽约2,近基端弯折,远端一侧呈膜状增宽,似镰刀状。阴道弯管状,长30～35;受精囊大小25×15。 新种在后吸器和交接器的形态构造上与寄生于两种蝴蝶鱼Chaetodon miliaris（模式宿主）、C．multicinctus的杯阴海盘虫H．scyphovagina Yamzguti,1968近似。但二者的支持器不同,已知种的支持器为一鞭状细丝,新种则为一较长而弯折的细条状,且远端一侧呈膜状增宽,似镰刀状。     

Five new monogenean species from the gills of Mulloidichthys vanicolensis (Perciformes: Mullidae) off New Caledonia, with the proposal of Volsellituba n. g. and Pennulituba n. g. (Monogenea: Dactylogyridae)

Three species of Volsellituba n. g. and two species of Pennulituba n. g. are described from the gills of the yellowfin goatfish Mulloidichthys vanicolensis (Valenciennes) off New Caledonia (South Pacific). Volsellituba and Pennulituba resemble dactylogyrid genera whose species lack eye-spots and possess tandem or slightly overlapping gonads, a single prostatic reservoir, a male copulatory organ without an accessory piece, a dextroventral non-sclerotised vagina, ventral and dorsal anchor/bar complexes, and hooks with shanks comprising a single slender unit. Volsellituba n. g. is characterised by its species having ventral tegumental folds at the level of the vaginal duct, a male copulatory organ with a subterminal basal opening and a two-piece dorsal bar. The following new species of Volsellituba are described: V. orchidea n. sp. (type-species), V. nabla n. sp. and V. elephantina n. sp. Pennulituba n. g. is distinguished by its species possessing a male copulatory organ with a wing-shaped membrane and a dorsal bar with a poorly to non-sclerotised medial part. This genus includes P. piratifalx n. sp. (type-species) and P. cymansis n. sp. A tabular summary of the species of Haliotrema Johnston & Tiegs, 1922 reported from mullids is provided.     

Septesinus gibsoni n. g., n. sp. (Monocotylidae: Heterocotylinae), from the gills of Himantura walga (Dasyatidae) off Sarawak, Borneo

Septesinus gibsoni n. g., n. sp. (Monocotylidae: Heterocotylinae) is described from the gills of the dwarf whipray Himantura walga (Müller & Henle) collected in marine waters off Sarawak (Borneo), Malaysia. Septesinus n. g. is distinguished from other genera in the Monocotylidae by a combination of characters, including a haptor with one central and seven peripheral loculi, the presence of a highly sinuous ridge surmounting all haptoral septa, four rounded accessory structures on the dorsal surface of the haptor, and the anterior region with two pairs of anteromedian and three pairs of anterolateral gland-duct openings. Septesinus n. g. is accommodated in the Heterocotylinae. Septesinus gibsoni n. sp. is described and fully illustrated, and a key to the genera of Heterocotylinae is provided. The composition of the ridges surrounding the mouth of a number of heterocotyline species and their usefulness as a taxonomic character are examined. The identity of four specimens of Monocotyle Taschenberg, 1878, also recovered from the gills of this host species, is discussed.     

Empruthotrema kearni n. sp. and observations on Thaumatocotyle pseudodasybatis Hargis, 1955 (Monogenea: Monocotylidae) from the nasal fossae of Aetobatus narinari (Batiformes: Myliobatidae) from Moreton Bay,Queensland

Empruthotrema kearni n. sp. and Thaumatocotyle pseudodasybatis Hargis, 1955 (Monogenea: Monocotylidae) are reported from the nasal fossae of the spotted eagle ray, Aetobatus narinari Euphrasen, 1790, from Moreton Bay, Queensland, Australia. The discovery of E. kearni n. sp. is the first record of this genus from the Myliobatidae and a new geographical record for the genus. A comparison of T. pseudodasybatis from Florida, USA and from Queensland, Australia revealed morphometrical and microhabitat differences. The discovery of T. pseudodasybatis in Australian waters is a new geographical record for this species.     

Bucephaline digeneans (Bucephalidae) in <Emphasis Type="Italic">Sphyraena putnamae</Emphasis> Jordan &; Seale (Sphyraenidae) from the lagoon off New Caledonia

Lethrinitrema gibbus n. g., n. sp. and L. dossenus n. sp. are described from the fish Lethrinus rubrioperculatus Sato collected off New Caledonia, South Pacific. Members of Lethrinitrema n. g. (Ancyrocephalidae) are characterised by having two pyriform haptoral reservoirs and ventral anchors with lateral grooves. The elongate tubular distal end of each reservoir bifurcates, draining into a superficial lateral groove on each side of the ventral anchors. The haptoral reservoirs are postulated to store secretory products which assist in attachment to the host. Lethrinitrema spp. also possess tandem gonads, a male copulatory organ without an accessory piece or with thinly sclerotised accessory piece, and a dextrolateral, non-sclerotised vaginal bulb. The two new species have small, poorly demarcated haptors with small haptoral armament and a crown-like piece on the tip of the inner root of the ventral anchors. They differ from each other in the shape and size of the ventral bar and male copulatory organ (40–45 μm in length in L. gibbus vs 24–30 μm in L. dossenus). Three other species, previously included in Haliotrema Johnston & Tiegs, 1922, are transferred to Lethrinitrema, i.e. L. chrysostomi (Young, 1968) n. comb., L. fleti (Young, 1968) n. comb. (both briefly redescribed from paratypes) and L. lethrini (Yamaguti, 1937) n. comb. All species of Lethrinitrema parasitise Lethrinus spp. (Lethrinidae), and there is evidence for the existence of further Lethrinitrema spp. on Lethrinus spp. in the Indo-Pacific region.     

The status of Acleotrema Johnston & Tiegs, 1922 and Heteroplectanum Rakotofiringa, Oliver & Lambert, 1987 (Monogenoidea: Diplectanidae), with the redescription of Acleotrema girellae Johnston & Tiegs, 1922

Acleotrema Johnston & Tiegs, 1922 is resurrected and its diagnosis amended. A. girellae Johnston & Tiegs, 1922 is redescribed based on the lectotype from the Australian Museum (Sydney, Australia). A. kyphosi Yamaguti, 1968 is considered a junior synonym of A. girellae. Heteroplectanum Rakotofiringa, Oliver & Lambert, 1987 is considered a junior synonym of Acleotrema. The nine species of the latter genus are transferred to Acleotrema as: A. diplobulbus (Yamaguti, 1968) n. comb., A. nenue (Yamaguti, 1968) n. comb., A. spiculare (Yamaguti, 1968) n. comb., A. yamagutii (Oliver, 1983) n. comb., A. nenuoides (Rakotofiringa, Oliver & Lambert, 1987) n. comb., A. parastromatei (Rakotofiringa, Oliver & Lambert, 1987) n. comb., A. serrulopenis (Rakotofiringa, Oliver & Lambert, 1987) n. comb., A. tamatavense (Rakotofiringa, Oliver & Lambert, 1987) n. comb. and A. oliveri (León-Règagnon, Pérez-Ponce de León & Garcia- Prieto, 1997) n. comb. An historical account of the species of Acleotrema is presented.     

Three new species of Protogyrodactylus Johnston & Tiegs, 1922 (Monogenoidea: Dactylogyridae) from the gills of the longtail silverbiddy Gerres longirostris (Teleostei: Gerreidae) in the Red Sea

Twenty-one specimens of the longtailed silverbiddy Gerres longirostris (Gerreidae) were examined for dactylogyrid parasites from the Nabq Managed Resource Protected Area, Ras Mohammed National Park (Red Sea) near Sharm El-Sheikh, South Sinai, Egypt. The diagnosis of Protogyrodactylus Johnston & Tiegs, 1922 was amended, and three new species, P. federicae n. sp., P. zullinii n. sp. and P. alatus n. sp., were recovered and described; the prevalence of each species was 100%. P. federicae most closely resembled P. alienus Bychowsky & Nagibina, 1974, but differed from it by possessing two anteromedial projections on the ventral bar, a claw-like ventral anchor sclerite and spatulate dorsal bars. P. zullini was most similar to P. quadratus Johnston & Tiegs, 1922, from which it differed by having a distal hook on the superficial root of the dorsal anchor, an evenly curved ventral anchor shaft and point, and a flange on the bulbous base of the male copulatory organ. P. alatus was closest to P. youngi Bychowsky & Nagibina, 1974, from which it differed by having delicate anchors and two prominent anteromedial processes on the ventral bar.     

The phylogenetic position of the Loimoidae Price, 1936 (Monogenoidea: Monocotylidea) based on analyses of partial rDNA sequences and morphological data

Phylogenetic analyses of partial sequences of 18S and 28S rDNA of some monogenoids, including monocotylids and a specimen of Loimosina sp. collected from a hammerhead shark off Brazil, indicated that the Loimoidae (as represented by the specimen of Loimosina sp.) represents an in-group taxon of the Monocotylidae. In all analyses, the Loimoidae fell within a major monocotylid clade including species of the Heterocotylinae, Decacotylinae, and Monocotylinae. The Loimoidae formed a terminal clade with two heterocotyline species, Troglocephalus rhinobatidis and Neoheterocotyle rhinobatis, for which it represented the sister taxon. The following morphological characters supported the clade comprising the Loimoidae, Heterocotylinae, Decacotylinae and Monocotylinae: single vagina present, presence of a narrow deep anchor root, and presence of a marginal haptoral membrane. The presence of cephalic pits was identified as a putative synapomorphy for the clade (Loimoidae (T. rhinobatidis, N. rhinobatis)). Although rDNA sequence data support the rejection of the Loimoidae and incorporating its species into the Monocotylidae, this action was not recommended pending a full phylogenetic analysis of morphological data.     

Monogenoidean parasites of the gill lamellae of the sheepshead Archosargus probatocephalus (Walbaum) (Perciformes: Sparidae) from the Indian River Lagoon, Florida, with descriptions of four new species of Euryhaliotrema Kritsky & Boeger, 2002 (Dactylogyridae)

Examination of the gill lamellae of three sheepshead Archosargus probatocephalus (Walbaum) from the Indian River Lagoon in Florida revealed six species of Monogenoidea: Microcotyle archosargi MacCallum, 1913 (Microcotylidae); Neobenedenia sp. (Capsalidae); and four new species of Euryhaliotrema Kritsky & Boeger, 2002 (Dactylogyridae). The prevalence of all helminths was 100%, except for Neobenedenia sp., which was represented by a single immature specimen. The four new species, Euryhaliotrema carbuncularium n. sp., E. dunlapae n. sp., E. amydrum n. sp. and E. spirulum n. sp., are described and with E. carbunculus (Hargis, 1955) Kritsky & Boeger, 2002 apparently constitute a monophyletic clade of Euryhaliotrema spp. that parasitise sparid hosts in the western hemisphere. The Indian River Lagoon in Florida represents a new locality record for M. archosargi, and the sheepshead is apparently a new host record for a member (Neobenedenia sp.) of the Capsalidae.     

A new species of <Emphasis Type="Italic">Neoheterocotyle</Emphasis> Hargis, 1955 (Monogenea: Monocotylidae) from the gills of <Emphasis Type="Italic">Rhinobatos annulatus</Emphasis> Müller &; Henle (Rhinobatidae) off the southern tip of Africa

Neoheterocotyle robii n. sp. is described from the gills of four female Rhinobatos annulatus Müller & Henle caught as bycatch during routine demersal research trawls off the Southern Cape coast of South Africa. The new species can be distinguished from all other members of Neoheterocotyle Hargis, 1955 by the morphology of the accessory piece associated with the male copulatory organ, the presence of a distinct horseshoe-shaped muscle associated with the male copulatory organ and the presence of a sclerotised structure in the proximal portion of the vagina. This is the first Neoheterocotyle species described from South African waters.     

A phylogenetic analysis and systematic revision of the cryptobranch dorids (Mollusca, Nudibranchia, Anthobranchia)

The phylogenetic relationships of the cryptobranch dorids are studied based on morphological characters of species belonging to all previously described genera. The phylogenetic hypothesis supports the cryptobranch dorids as a monophyletic group. There are two major clades within the Cryptobranchia: the radula‐less dorids (Porostomata), and the radula‐bearing dorids ( Labiostomata new taxon ). Labiostomata consists of those taxa sharing a more recent common ancestor with Actinocyclus than with Mandelia, and includes several monophyletic groups: Actinocyclidae, Chromodorididae, Dorididae and Discodorididae. The traditional group Phanerobranchia is probably paraphyletic. The new classification proposed for the Cryptobranchia addresses concepts of phylogenetic nomenclature, but is in accordance with the rules of the International Code of Zoological Nomenclature. The following genera of cryptobranch dorids are regarded as valid: Doris Linnaeus, 1758, Asteronotus Ehrenberg, 1831, Atagema J. E. Gray, 1850, Jorunna Bergh, 1876, Discodoris Bergh, 1877, Platydoris Bergh, 1877, Thordisa Bergh, 1877, Diaulula Bergh, 1878, Aldisa Bergh, 1878, Rostanga Bergh, 1879, Aphelodoris Bergh, 1879, Halgerda Bergh, 1880, Peltodoris Bergh, 1880, Hoplodoris Bergh, 1880, Paradoris Bergh, 1884, Baptodoris Bergh, 1884, Geitodoris Bergh, 1891, Gargamella Bergh, 1894, Alloiodoris Bergh, 1904, Sclerodoris Eliot, 1904, Otinodoris White, 1948, Taringa Er. Marcus, 1955 , Sebadoris Er. Marcus & Ev. Marcus, 1960, Conualevia Collier & Farmer, 1964, Thorybopus Bouchet, 1977, Goslineria Valdés, 2001, Pharodoris Valdés, 2001, Nophodoris Valdés & Gosliner, 2001. Several genera previously considered as valid are here regarded as synonyms of other names: Doridigitata d’Orbigny, 1839, Doriopsis Pease, 1860, Staurodoris Bergh, 1878, Fracassa Bergh, 1878, Archidoris Bergh, 1878, Anoplodoris Fischer, 1883, Etidoris Ihering, 1886, Phialodoris Bergh, 1889, Montereina MacFarland, 1905, Ctenodoris Eliot, 1907, Carryodoris Vayssière, 1919, Austrodoris Odhner, 1926, Guyonia Risbec, 1928, Erythrodoris Pruvot‐Fol, 1933, Neodoris Baba, 1938, Siraius Er. Marcus, 1955, Tayuva Ev. Marcus & Er. Marcus, 1967, Nuvuca Ev. Marcus & Er. Marcus, 1967, Doriorbis Kay & Young, 1969, Pupsikus Er. Marcus & Ev. Marcus, 1970, Percunas Ev. Marcus, 1970, Verrillia Ortea & Ballesteros, 1981 . The genera Artachaea Bergh, 1882, Carminodoris Bergh, 1889 and Homoiodoris Bergh, 1882 have been poorly described and no type material is known to exist. They are regarded as incertae sedis until more material becomes available. The genus names Xenodoris Odhner in Franc, 1968 and Cryptodoris Ostergaard, 1950 are unavailable within the meaning of the Code. Hexabranchus Ehrenberg, 1831 is not a cryptobranch dorid, as suggested by other authors, because of the lack of a retractile gill. Other nomenclatural and taxonomic problems are discussed, and several type species, neotypes and lectotypes are selected. © 2002 The Linnean Society of London. Zoological Journal of the Linnean Society, 2002, 136 , 535?636.     

Morphological and molecular evolution are not linked in Lamellodiscus (Plathyhelminthes, Monogenea)

Lamellodiscus Johnston & Tiegs 1922 (Monogenea, Diplectanidae) is a genus of common parasites on the gills of sparid fishes. Here we show that this genus is probably undergoing a fast molecular diversification, as reflected by the important genetic variability observed within three molecular markers (partial nuclear 18S rDNA, Internal Transcribed Spacer 1, and mitonchondrial Cytochrome Oxidase I). Using an updated phylogeny of this genus, we show that molecular and morphological evolution are weakly correlated, and that most of the morphologically defined taxonomical units are not consistent with the molecular data. We suggest that Lamellodiscus morphology is probably constrained by strong environmental (host-induced) pressure, and discuss why this result can apply to other taxa. Genetic variability within nuclear 18S and mitochondrial COI genes are compared for several monogenean genera, as this measure may reflect the level of diversification within a genus. Overall our results suggest that cryptic speciation events may occur within Lamellodiscus, and discuss the links between morphological and molecular evolution.     

Studies on Lethrinitrema Lim & Justine, 2011 (Monogenea: Dactylogyridae), with the description of two new species,a key to the genus and a phylogenetic analysis based on rDNA sequences

Six species of Lethrinitrema Lim & Justine, 2011, including two new taxa, are described from the gills of Lethrinus nebulosus (Forsskål) from the South China Sea. Lethrinitrema nebulosum n. sp. differs from all other members of the genus in possessing a copulatory organ with a short, distally recurved tube, a cup-shaped base and a thin accessory piece, arising from distal end of tube, junction inconspicuous. Lethrinitrema zhanjiangense n. sp. can be distinguished from its congeners by possessing a copulatory organ with a C-shaped tube, a cup-shaped base and without accessory piece. Lethrinitrema grossecurvitubum (Li & Chen, 2005) n. comb. and Lethrinitrema austrosinense (Li & Chen, 2005) n. comb., previously included in Haliotrema Johnston & Tiegs, 1922, are transferred to Lethrinitrema and redescribed with additional details, including the intestinal caeca that unite posterior to gonads and continue posteriorly as two diverticula, and the elongate tubular distal end of each haptoral reservoir bifurcating prior to entering a superficial lateral groove on each side of the ventral anchor. The sclerotised parts of two unidentified species of Lethrinitrema are also described. Lethrinitrema sp. 1 differs from the other Lethrinitrema spp. in possessing a male copulatory organ consisting of a short tapered tube with a robust cup-shaped base and in lacking accessory piece. Lethrinitrema sp. 2 differs from its congeners in possessing a copulatory organ comprised of a short slender tube and without accessory piece, delicate ventral and dorsal bars, and poorly developed outer roots of the anchors. Sequences of partial 28S rDNA (domains D1–D2) and complete 18S rDNA for 27 dactylogyrids including five species of Lethrinitrema, i.e. Lethrinitrema fleti (Young, 1968) Lim & Justine, 2011, L. nebulosum, L. zhanjiangense, L. grossecurvitubum and Lethrinitrema sp. 1 were used to assess the monophyly of Lethrinitrema which was supported by high bootstrap values.