Monogenea

This study focuses on the phylogenetic relationships within the Polyopisthocotylea and Monopisthocotylea, two groups that are often grouped within the monogeneans, a group of disputed paraphyly. Phylogenetic analyses were conducted with multiple outgroups chosen according to two hypotheses, a paraphyletic Monogenea or a monophyletic Monogenea, and with three methods, namely maximum parsimony, neighbour joining and maximum likelihood. Sequences used were from the partial domain C1, full domain D1, and partial domain C2 (550 nucleotides, 209 unambiguously aligned sites) from the 28S ribosomal RNA gene for 16 species of monopisthocotyleans, 26 polyopisthocotyleans including six polystomatids, and other Platyhelminthes (61 species in total, 27 new sequences). Results were similar with outgroups corresponding to the two hypotheses. Within the Monopisthocotylea, relationships were: {[(Udonella, capsalids), monocotylids], (diplectanids, ancyrocephalids)}; each of these families was found to be monophyletic and their monophyly was supported by high bootstrap values in neighbour joining and maximum parsimony. Within the Polyopisthocotylea, the polystomatids were the sister-group of all others. Among the latter, Hexabothrium, parasite of chondrichthyans, was the most basal, and the mazocraeids, mainly parasites of clupeomorph teleosts, were the sister-groups of all other studied polyopisthocotyleans, these, mainly parasites of euteleosts, being polytomous.

Trematodes belonging to the Phylum Platyhelminth are poorly studied in fishes of Karachi coast and the literature is also widely
scattered. Shaukat and Bilqees prepared a check list of Trematodes in 2005. But later no such work was conducted. Therefore; it was
desired to prepare an updated checklist of Trematodes from Karachi coast. At present, a total of 198 species of trematodes are known
from the Karachi coast of Pakistan reported by various authors.

Chapter I. Material and methods
1. Material
A list of the parasites studied (and their hosts) is given: about 40 species of Monogeneans, 10 Digeneans, some Cestodes and Temnocephala.
2. Methods
The methods used for parasite collection, light and transmission electron microscopy are described.

Chapter II. Descriptive study of spermiogenesis and spermatozoa
1. Gross structure of the testis
The testis contains supporting cells, and germinal cells which are grouped in a common cytoplasmic mass at the spermatid stage. The evolution of this mass is described.
2. Spermiogenesis
A "classical" spermiogenesis is described in the Digeneans: 7 stages are defined. This spermiogenesis is also found in the Polyopisthocotylean Monogeneans. The various processes of spermiogenesis of other species may be compared with the "classical" spermiogenesis; they show modifications which are generally simplifications. A general Table showing the possible homologies between the stages of spermiogenesis found in the different species is proposed. In the case of the schistosome, after analysing the spermiogenesis, we suggest considering its aberrant spermatozoon as "neotenic", because it resembles a precociously matured spermatid. The fate and possible role of two organelles of the spermatid which are absent in the spermatozoon, the centre body and the striated roots, are considered. The process of separation of the nature spermatozoon is discussed. The aberrant case of the Polyopisthocotylean Monogenean Diplozoon is underlined, because it is the single case which cannot be compared with the "classical" spermiogenesis. The spermiogenesis of Monogeneans and Digeneans is compared with that of the other Platyhelminthes: it is close to that of Cestodes, but it shows fundamental differences from that of Turbellarians, in spite of a superficial resemblance of the spermatozoa.
3. Structure of the mature spermatozoa
Spermatozoa of Digeneans and Monogeneans are generally filiform. A Table compares the length of spermatozoa in various species. A "classical" pattern of spermatozoon (or type 1) is described: it comes from the "classical" spermiogenesis. The "classical" spermatozoon contains two axonemes incorporated in the sperm body and cortical longitudinal microtubules. This "classical" pattern is almost universal within Digeneans and Polyopisthocotylean Monogeneans, but is unknown in the Monopisthocotylean Monogeneans. It also exists, in a slightly modified form, in some Cestodes. Spermatozoa of the Monopisthocotylean Monogeneans are classified by means of two simple ultrastructural characteristics, the number of axonemes (1 or 2) and the presence of cortical microtubules, in three patterns (types 2, 3 and 4). The cases of the Digenean Schistosoma (non filiform) and of the Polyopisthocotylean Monogenean Diplozoon (aflagellate) are aberrant and set aside. Comparative diagrams are presented.
4. The organelles of the spermatozoon and their evolution during spermiogenesis
Centrioles of mature spermatozoa are atypical and are generally made up of 9 singlets, instead of the typical structure of triplets found in the spermatids. The axonemes show a special pattern, called 9+ ''1 "; the few variations are presented. The ornamentations associated with the membrane are described. The position of the nucleus is discussed: it is posterior, meaning that spermatozoa of Digeneans and Monogeneans are "inverted" compared with those of other animals. Coils of spermatozoa found in some species are considered to be details added to a fundamentally filiform structure.
5. Motility of spermatozoa
Comparative Tables of spermatozoan motility and ultrastructure (axonemes and microtubules) are given. It is impossible to correlate in a precise manner ultrastructure and motility.
6. Behaviour of the spermatozoa during fertilization
The spermatozoa penetrate the oocyte with the nucleus in a posterior position; available data concern only few species, mainly with "classical" spermatozoa.
7. Partial conclusion after chapter II
Data advanced in this chapter are summarised and discussed.

Chapter III. Morphology of spermatozoa, biology of fertilization and phylogeny
1. Introduction
Some classical cases of the literature are considered.
2. Spermatozoa and biology of fertilization
The "classical" spermatozoon (type 1 ) of the Digeneans and Polyopisthocotylean Monogeneans seems to be linked with internal fertilization, through genital ducts (Digeneans) or by hypodermic injection (at least a part of the Polyopisthocotylean Monogeneans). In the monopisthocotylean Monogeneans (with spermatozoa of types 2, 3 and 4), the literature mentions some cases of spermatophores, but it is not possible to establish a strict relationship between these sperm structures and fertilization by spermatophore. The case of the Polyopisthocotylean Monogenean Diplozoon is interesting. In this animal, the biology of fertilization is unique because the two members of the pair are fused, and the spermatozoon is the only aflagellate case known: it displays a remarkable correlation between the biology of fertilization and sperm structure. The case of the schistosomes is discussed. Attempts are made to relate the atypical structure of the spermatozoon to the peculiar characteristics of the schistosomes: gonochorism, progenesis, life in pairs. It seems that life in permanent pairs is a factor of differentiation of atypical sperm structures, in the schistosomes, Diplozoon, and some Didymozoonidae.
3. Spermatozoa and phylogeny
Relationships between phylogeny, taxonomy, biology of fertilization and sperm structure are discussed. In the Trematodes (Digeneans and Aspidogastreans), the sperm structure is very homogenous (type 1) and thus of little use for the understanding of phylogeny within this group. The few variations known (Didymozoata and Strigeata) seem to be linked mainly with the biology of fertilization rather than with phylogeny. In the Monogeneans, comparative spermatology allows us to separate Polyopisthocotyleans and Monopisthocotyleans. Polyopisthocotylean Monogeneans are very homogenous and share type 1 with the Trematodes. The single really different case, Diplozoon, seems to have no phyletic value but is correlated with the biology of fertilization. Monopisthocotylean Monogeneans show three types of spermatozoa. A phyletic scheme built only from sperm ultrastructure shows resemblances with classical phylogenies drawn from the structure of the adults, and a remarkable coincidence with modern phylogenies elaborated from the structure of larvae. The case of the Monogeneans is thus a demonstrative example of the usefulness of comparative spermatology for the understanding of phylogeny.
4. Trends in the evolution of spermatozoa in parasitic Platyhelminthes
Spermatozoa of Platyhelminthes are generally biflagellate. After a comparative study, we consider that the less evolved spermatozoon in the parasitic Platyhelminthes (Monogeneans, Digeneans and Cestodes) is the "classical" type, or type 1. This type 1 is maintained in the Digeneans and Polyopisthocotylean Monogeneans, but is modified in the Cestodes (loss of the mitochondrion, and of one axoneme in some cases), and in the Monopisthocotylean Monogeneans (loss of the microtubules am of one axoneme). The origin of type 1 may possibly be found in the Turbellaria Rhabdocoela Kalyptorhynchia. Comparative and phyletic diagrams of sperm structure in the phylum Platyhelminthes are given.

Parasite biodiversity of fish of the southern part of the Mediterranean sea is still incompletely explored. We describe here Microcotyle visa n. sp. from the gill filaments of the bluespotted seabream Pagrus caeruleostictus (Valenciennes) (Sparidae) collected off the Algerian coast. The identity of fish hosts was confirmed by barcoding. Microcotyle visa n. sp. is herein described and illustrated. Analysis of the cox1 gene of the monogeneans revealed minor intraspecific variation (1.4{\%}), an order of magnitude lower than the distance between this species and other Microcotyle species (10--15 {\%}). Microcotyle visa n. sp. is distinguished from Microcotyle erythrini van Beneden {\&} Hesse, 1863, a congener infesting sparids, on the basis of morphological (size of clamps, number of testes) and molecular (cox1) differences. This is the fourth member of the genus known to parasitise a sparid host. A species of Paramicrocotyle sp. included in the molecular analysis was nested within a robust Microcotyle + Paramicrocotyle clade; in the absence of demonstrated molecular and morphological differences, we consider that Paramicrocotyle Caballero {\&} Bravo-Hollis, 1972 is a junior synonym of Microcotyle van Beneden {\&} Hesse, 1863 and transfer two species of Paramicrocotyle as Microcotyle danielcarrioni (Martinez {\&} Barrantes, 1977) n. comb. and Microcotyle moyanoi (Villalba {\&} Fernandes, 1986) n. comb.

Bu çalışma, Eylül 2014-Mart 2015 tarihleri arasında Ege Denizi kökenli (İzmir ve Çanakkale açıkları) 50 adet sıçrayan kefal balığı örneğinin Liza saliens (Risso, 1810)’nın helmintlerinin araştırılmasını kapsamaktadır. Liza saliens’te Monogenea’dan 1 tür (Microcotyle mugilis), Acanthocephala’dan 1 tür (Neoechinorhynchus agilis) ve Nematoda’dan 2 farklı taksona (Contracaecum sp. ve Philometra sp.) ait helmintler gözlenmiştir. Çalışma sonucunda elde edilen verilere göre Liza saliens, Microcotyle mugilis, Philometra sp. ve Contracaecum sp. taksonları için Türkiye’den yeni konak kaydı olarak belirlenmiştir.

Ectoparasites face a daily challenge: to remain attached to their hosts. Polyopisthocotylean monogeneans usually attach to the surface of fish gills using highly specialized structures, the sclerotized clamps. In the original description of the protomicrocotylid species Lethacotyle fijiensis, described 60 years ago, the clamps were considered to be absent but few specimens were available and this observation was later questioned. In addition, genera within the family Protomicrocotylidae have either clamps of the ‘‘gastrocotylid’’ or the ‘‘microcotylid’’ types; this puzzled systematists because these clamp types are characteristic of distinct, major groups. Discovery of another, new, species of the genus Lethacotyle, has allowed us to explore the nature of the attachment structures in protomicrocotylids. Lethacotyle vera n. sp. is described from the gills of the carangid Caranx papuensis off New Caledonia. It is distinguished from Lethacotyle fijiensis, the only other species of the genus, by the length of the male copulatory spines. Sequences of 28S rDNA were used to build a tree, in which Lethacotyle vera grouped with other protomicrocotylids. The identity of the host fish was confirmed with COI barcodes. We observed that protomicrocotylids have specialized structures associated with their attachment organ, such as lateral flaps and transverse striations, which are not known in other monogeneans. We thus hypothesized that the clamps in protomicrocotylids were sequentially lost during evolution, coinciding with the development of other attachment structures. To test the hypothesis, we calculated the surfaces of clamps and body in 120 species of gastrocotylinean monogeneans, based on published descriptions. The ratio of clamp surface: body surface was the lowest in protomicrocotylids. We conclude that clamps in protomicrocotylids are vestigial organs, and that occurrence of ‘‘gastrocotylid’’ and simpler ‘‘microcotylid’’ clamps within the same family are steps in an evolutionary sequence, leading to the absence of these attributes in species of Lethacotyle.

Based on a molecular and morphological study, a new monocotylid genus, Holocephalocotyle n. gen. is proposed to accommodate Holocephalocotyle monstrosae n. sp., found on the olfactory rosette of the rabbit fish, Chimaera monstrosa Linnaeus (Chondrichthyes, Chimaeridae), from the Mediterranean Sea off Algeria. Identification of fish hosts was confirmed by molecular barcoding of the COI gene. A partial 28S rDNA sequence (D1-D2 domain) of Holocephalocotyle monstrosae was obtained; it was distinct from all known monocotylid sequences (p-distance: 15.5-23%). A phylogenetic tree constructed from available monocotylid sequences showed that Holocephalocotyle monstrosae was included, and basal, in a robust group including species of Merizocotyle, Mycteronastes and Empruthotrema, confirming that the species is a member of the Merizocotylinae. The new genus is unique among the Merizocotylinae in having a distinctive pattern of haptoral loculi with one central, five peripheral and seven "interperipheral loculi" partially inserted between peripheral loculi and a compartmentalised sclerotised male copula-tory organ. The diagnosis of the Merizocotylinae is amended to include this new genus. The new genus represents the second monocotylid genus recorded from holocephalans. Ré sumé-Holocephalocotyle monstrosae n. gen. n. sp. (Monogenea, Monocotylidae) de la rosette olfactive de la chimère Chimaera monstrosa (Holocephali, Chimaeridae) en mer profonde au large de l'Algérie. Sur la base d'une étude moléculaire et morphologique, un nouveau genre de Monocotylidae, Holocephalocotyle n. gen. est proposé pour accueillir Holocephalocotyle monstrosae n. sp., trouvé sur la rosette olfactive de la chimère Chimaera monstrosa Linnaeus (Chondrichthyes, Chimaeridae) de la mer Méditerranée au large de l'Algérie. L'identification des hôtes poissons a été confirmée par code-barre moléculaire du gène COI. Une séquence partielle d'ADNr 28S (domaine D1-D2) d'Holocephalocotyle monstrosae a été obtenue et était distincte de toutes les séquences de Monocotylidae connues (p-distance : 15.5-23 %). Un arbre phylogénétique construit à partir des séquences de Monocotylidae disponibles a montré qu'Holocephalocotyle monstrosae était inclus et basal dans un groupe robuste comprenant des espèces de Merizocotyle, Mycteronastes et Empruthotrema, confirmant que l'espèce est membre des Merizocotylinae. Le nouveau genre est unique parmi les Merizocotylinae en ce qu'il présente un motif distinctif de loculi haptoraux avec un loculus central, 5 périphériques et 7 « loculi intra-périphériques » partiellement insérés entre des loculi périphériques, et un organe copulateur mâle sclérifié compartimenté. La diagnose des Merizocotylinae est modifiée pour inclure ce nouveau genre. Le nouveau genre représente le deuxième genre de Monocotylidae répertorié chez les holocéphales.

Three new species of Lamellodiscus are described from four (including two undescribed) species of Gymnocranius off New Caledonia, South Pacific. All three species have a similar body anatomy and morphology of the haptoral hard parts and are distinguished on the basis of the male copulatory organ (MCO). Lamellodiscus tubulicornis n. sp. (type-host: G. grandoculis; other host: Gymnocranius sp. B) has an MCO with a tube and horn; L. magnicornis n. sp. (type-host: G. grandoculis; other hosts: G. euanus, Gymnocranius sp. A and Gymnocranius sp. B) has an MCO with a long horn and a membrane; L. parvicornis n. sp. (type-host: G. euanus; other hosts: G. grandoculis and Gymnocranius sp. B) has anMCOwith a small horn and a membrane. Lamellodiscus epsilon Yamaguti, 1968 is redescribed based on the type-specimens (from Monotaxis grandoculis off Hawaii). Lamellodiscus sp. is recorded from Gnathodentex aureolineatus off New Caledonia. All these five species have lamellodiscs that exhibit a unique characteristic: the second lamella forms an almost closed circle, in contrast to all other described species of Lamellodiscus in which the second lamella has the form of one or two crescents. Lamellodiscus spp. are usually classified in two groups, the ‘ignoratus’ and ‘elegans’ groups, according to the structure of the lamellodisc; we propose a new ‘tubulicornis’ group for these five species. In addition to their lamellodisc structure, species of the tubulicornis group are also characterised by their egg (elongate in contrast to tetrahedral in the two other groups) and their hosts (monotaxine lethrinids as opposed to mainly sparids). The generic diagnosis of Lamellodiscus given by Amine & Euzet (2005) is amended to include species with elongate eggs.

Sperm ultrastructure provides morphological characters useful for understanding phylogeny; no study was available for two basal branches of the Polyopisthocotylea, the Chimaericolidea and Diclybothriidea. We describe here spermiogenesis and sperm in Chimaericola leptogaster (Chimaericolidae) and Rajonchocotyle emarginata (Hexabothriidae), and sperm in Callorhynchocotyle callorhynchi (Hexabothriidae). Spermiogenesis in C. leptogaster and R. emarginata shows the usual pattern of most Polyopisthocotylea with typical zones of differentiation and proximo-distal fusion of the flagella. In all three species, the structure of the spermatozoon is biflagellate, with two incorporated trepaxonematan 9 + " 1 " axonemes and a posterior nucleus. However, unexpected structures were also seen. An alleged synapomorphy of the Polyopisthocotylea is the presence of a continuous row of longitudinal microtubules in the nuclear region. The sperm of C. leptogaster has a posterior part with a single axoneme, and the part with the nucleus is devoid of the continuous row of microtubules. The spermatozoon of R. emarginata has an anterior region with membrane ornamentation, and posterior lateral microtubules are absent. The spermatozoon of C. callorhynchi has transverse sections with only dorsal and ventral microtubules, and its posterior part shows flat sections containing a single axoneme and the nucleus. These findings have important implications for phylogeny and for the definition of synapomorphies in the Neodermata. We point out a series of discrepancies between actual data and interpretation of character states in the matrix of a phylogeny of the Monogenea. Our main conclusion is that the synapomorphy " lateral microtubules in the principal region of the spermatozoon " does not define the Polyopisthocotylea but is restricted to the Mazocraeidea.


Résumé-Spermiogenèse et ultrastructure des spermatozoïdes chez les Monogènes Polyopistho-cotylea basaux Hexabothriidae et Chimaericolidae, et leur signification pour la phylogénie des Monogenea. L'ultrastructure des spermatozoïdes fournit des caractères morphologiques utiles pour comprendre la phylogénie ; aucune étude n'était disponible pour deux branches basales des Polyopisthocotylea, les Chimaericolidea et des Diclybothriidea. Nous décrivons ici la spermiogenèse et le spermatozoïde chez Chimaericola leptogaster (Chimaericolidae) et Rajonchocotyle emarginata (Hexabothriidae), et le spermato-zoïde chez Callorhynchocotyle callorhynchi (Hexabothriidae). La spermiogenèse chez C. leptogaster et R. emarginata montre le schéma habituel de la plupart des Polyopisthocotylea avec une zone de différenciation typique et une fusion proximo-distale des flagelles. Chez les trois espèces, la structure du spermatozoïde est biflagellée, avec deux axonèmes incorporés de type Trepaxonemata 9 + " 1 " et un noyau postérieur. Cependant, des structures inattendues ont également été observées. Une synapomorphie présumée des Polyopisthocotylea est la présence d'une rangée continue de microtubules longitudinaux dans la région nucléaire. Le spermatozoïde de C. leptogaster a une partie postérieure avec un seul axonème, et la partie avec le noyau est dépourvue de la rangée continue de microtubules. Le spermatozoïde de R. emarginata a une région antérieure avec ornementation membranaire et les microtubules postérieurs latéraux sont absents. Le spermatozoïde de C. callorhynchi a des coupes transversales montrant seulement des microtubules dorsaux et ventraux, et sa partie postérieure présente des coupes plates contenant un seul axonème et le noyau. Ces observations ont des implications importantes pour la phylogénie et la définition des synapomorphies des Neodermata. Nous signalons une série de divergences entre les données réelles et l'interprétation des états de caractères dans la matrice d'une phylogénie des Monogenea. Notre conclusion principale est que la synapomorphie « microtubules latéraux dans la région principale du spermatozoïde » ne définit pas les Polyopisthocotylea mais est limitée aux Mazocraeidea.

Platyhelminth phylogeny is controversial. Phylogenetic analyses of the partial domain C1 and the full domains D1 and C2 (358 nucleotides) from the 28S ribosomal RNA gene for 21 species from the Monogenea, Digenea, Cestoda, and, as the outgroup, Tricladida reveal major departures from prevailing theory. The Digenea and not the Monogenea (Monopisthocotylea and Polyopisthocotylea) form the sister group of the cestodes; the Monopisthocotylea and Polyopisthocotylea are each monophyletic, but the Monogenea do not form a monophylum; the sister group of the Digenea+Cestoda is the Polyopisthocotylea; and Monopisthocotylea are the sister group of all other parasitic flatworms.

This study describes the occurrence and molecular identification of Monogenea from blue-spotted flathead Platycephalus caeruleopunctatus (McCulloch) (Scorpaeniformes: Platycephalidae) from waters off the NSW coast, Australia. Platycephalus spp. are favoured by consumers for delicate, white, mild flavoured flesh and therefore are commercially important species within Australia. Platycephalus spp. are also extensively targeted by Australian recreational fishers. There has been no previous study that has exclusively focused on Pl. caeruleopunctatus in Australia or globally. Although a single study by Dillon (1985), of monogeneans infecting Platycephalus spp. from Australian waters, identified Microcotyle bassensis Murray, 1931 in Pl. caeruleopunctatus. The present study combines both morphological and molecular methods to identify both host and parasites. A total of 116 fish, sourced from the waters off the coast of New South Wales, Australia, were examined. A total of 1498 Monogenea were recovered from the gills. The overall prevalence, mean intensity, and mean abundance were 72%, 18.05, and 12.91, respectively. Monogenea were initially classified morphologically as two different species M. bassensis (family: Microcotylidae) and Platycephalotrema bassense (Hughes, 1928) Kritsky & Nitta, 2019 (family: Ancyrocephalidae). Molecular identification of Monogenea was conducted through sequencing of their mitochondrial cytochrome c oxidase subunit 1 (cox1) and nuclear 28S genes. The specific identification of host Pl. caeruleopunctatus was confirmed through sequencing the cox1 gene. There was no comparable sequence for cox1 and 28S genes available in GenBank for the monogenean species found in the present study. Only a single sequence (obtained from the nuclear ITS2-rDNA) was deposited in GenBank for M. bassensis. However, the phylogenetic analyses of mitochondrial and nuclear sequences revealed that the identified Monogenea clustered according to their familial groups. Platycephalotrema bassense was identified for the first time in Pl. caeruleopunctatus in the present study. This study has provided the first evidence for the exploration of both cox1 and 28S sequences of all Monogenea. The findings of this study serve as a foundation for future monogenean research on other Platycephalus spp. from Australian waters.

Neopolystoma moleri n. sp. and Neopolystoma grossi n. sp. are described as new polystome species on the eyes of Apaloneferox and Pseudemys concinna floridana, respectively from Florida, USA. Eleven other polystome species are currently knownfrom chelonian hosts in the USA, but only Neopolystoma elizabethae and Neopolystoma fentoni were described from the eye.Ocular polystomes are characterized as having spindle-shaped eggs; an exceptionally firm grip on the host; as well as the abilityto stretch, which gives them the advantage of being stationary while extending to feed, reducing the risk of being dislodged.The two new species can be distinguished from known Neopolystoma species by a combination of characteristics including marginal hooklet morphology.

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 lm in length in L. gibbus vs 24–30 lm 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.

"Background
Coral reefs are areas of maximum biodiversity, but the parasites of coral reef fishes, and especially their species richness, are not well known. Over an 8-year period, parasites were collected from 24 species of Lutjanidae, Nemipteridae and Caesionidae off New Caledonia, South Pacific.
Results
Host-parasite and parasite-host lists are provided, with a total of 207 host-parasite combinations and 58 parasite species identified at the species level, with 27 new host records. Results are presented for isopods, copepods, monogeneans, digeneans, cestodes and nematodes. When results are restricted to well-sampled reef fish species (sample size > 30), the number of host-parasite combinations is 20–25 per fish species, and the number of parasites identified at the species level is 9–13 per fish species. Lutjanids include reef-associated fish and deeper sea fish from the outer slopes of the coral reef: fish from both milieus were compared. Surprisingly, parasite biodiversity was higher in deeper sea fish than in reef fish (host-parasite combinations: 12.50 vs 10.13, number of species per fish 3.75 vs 3.00); however, we identified four biases which diminish the validity of this comparison. Finally, these results and previously published results allow us to propose a generalization of parasite biodiversity for four major families of reef-associated fishes (Lutjanidae, Nemipteridae, Serranidae and Lethrinidae): well-sampled fish have a mean of 20 host-parasite combinations per fish species, and the number of parasites identified at the species level is 10 per fish species.
Conclusions
Since all precautions have been taken to minimize taxon numbers, it is safe to affirm than the number of fish parasites is at least ten times the number of fish species in coral reefs, for species of similar size or larger than the species in the four families studied; this is a major improvement to our estimate of biodiversity in coral reefs. Our results suggest that extinction of a coral reef fish species would eventually result in the coextinction of at least ten species of parasites."

The presence/absence and number of vaginae is a major characteristic for the systematics of the Monogenea. Three gastrocotylid genera share similar morphology and anatomy but are distinguished by this character: Pseudaxine Parona & Perugia, 1890 has no vagina, Allogastrocotyle Nasir & Fuentes Zambrano, 1983 has two vaginae, and Pseudaxinoides Lebedev, 1968 has multiple vaginae. In the course of a study of Pseudaxine trachuri Parona & Perugia 1890, we found specimens with structures resembling “multiple vaginae”; we compared them with specimens without vaginae in terms of both morphology and molecular characterisitics (COI barcode), and found that they belonged to the same species. We also investigated the male copulatory organ (MCO) of this species, the accuracy of the original description of which is known to be a matter of debate. We found that the genital atrium is armed with 12 hooks arranged as a single circle and a central hollow stylet which is probably involved in traumatic ...

ABSTRACT: BACKGROUND: Coral reefs are areas of maximum biodiversity, but the parasites of coral reef fishes, and especially their species richness, are not well known. Over an 8-year period, parasites were collected from 24 species of Lutjanidae, Nemipteridae and Caesionidae off New Caledonia, South Pacific. RESULTS: Host-parasite and parasite-host lists are provided, with a total of 207 host-parasite combinations and 58 parasite species identified at the species level, with 27 new host records. Results are presented for isopods, copepods, monogeneans, digeneans, cestodes and nematodes. When results are restricted to well-sampled reef fish species (sample size[THIN SPACE]>[THIN SPACE]30), the number of host-parasite combinations is 20[EN DASH]25 per fish species, and the number of parasites identified at the species level is 9[EN DASH]13 per fish species. Lutjanids include reef-associated fish and deeper sea fish from the outer slopes of the coral reef: fish from both milieus wer...