Spermatological characters of the digenean Rubenstrema exasperatum (Rudolphi, 1819) (Plagiorchioidea, Omphalometridae)

Phyllodistomum vaili(Plagiorchiida: Gorgoderidae) infecting Parupeneus rubescens (Perciformes: Mullidae): morphology and phylogeny

Knowledge of the Arabian Gulf fish's parasite fauna is very poor. Until recently, only scattered reports from different locations are known for ecto- and endoparasites. Therefore, the present study aimed to investigate the digenean species that infects one of the most economically fish species in the Arabian Gulf, the rosy goatfish Parupeneus rubescens . One plagiorchiid species has been described, belonging to the Gorgoderidae family, and has been named as Phyllodistomum vaili Ho, Bray, Cutmore, Ward & Cribb, 2014 based on its morphological and morphometric characteristics. In order to accurately classify and characterize this plagiorchiid species, molecular analysis was carried out using both nuclear 18S and 28S rRNA gene regions and revealed that the present plagiorchiid species was associated with other species belonging to the Gorgoderidae family and deeply embedded in the Phyllodistomum genus, closely related to the previously described P. vaili (gb| KF013187.1, KF013173.1). The present study therefore revealed that the species Phyllodistomum is the first account as endoparasites from the rosy goatfish inhabiting the Arabian Gulf.

Spermatological characteristics of the family Glypthelminthidae (Digenea, Plagiorchioidea) inferred from the ultrastructural study of Glypthelmins staffordi Tubangui, 1928

The present study describes the ultrastructural organization of the mature spermatozoon of the digenean Glypthelmins staffordi (Glypthelminthidae) by means of transmission electron microscopy. Live digeneans were collected from the Chinese edible frog (Hoplobatrachus rugulosus) in Udon Thani Province (Thailand). The ultrastructural study reveals that the mature spermatozoon of G. staffordi is a filiform cell, which is tapered at both extremities. It exhibits the Bakhoum et al.'s type IV of spermatozoon of digeneans characterized by the 9+'1' axonemes of trepaxonematan Platyhelminthes, the presence of the association "external ornamentation-cortical microtubules", the external ornamentation located in the posterior part of the anterior region, the arrangement of parallel cortical microtubules in two bundles and with its maximum number located in the anterior part of the sperm cell, and the presence of two mitochondria. Other characteristics are the presence of spine-like bodies, a posterior extremity containing only the nucleus, and the presence of a large amount of glycogen granules. Results of the present study are particularly compared with the existing data in other families of the Plagiorchioidea, namely the Brachycoeliidae, the Haematoloechidae, the Omphalometridae and the Plagiorchiidae.

Advances in Spermatological Characters in the Digenea: Review and Proposal of Spermatozoa Models and Their Phylogenetic Importance

The wide biodiversity and economic importance of digeneans have motivated a great deal of research in the last decade, focussing on their phylogenetic positions. Molecular research was instrumental for our understanding of phylogeny in the Digenea, but spermatological studies have also provided many results, which are potentially useful for phylogeny; however, the complete spermatological data set has never been reviewed in a whole phylogenetic perspective. Spermatological data are now available for more than 100 species, belonging to 15 superfamilies and 46 families. In this paper, we try to summarize the current knowledge about sperm structure in the digeneans and propose a classification of digenean spermatozoa into five basic models. The main ultrastructural characters used are (1) the type of axoneme, (2) the lateral expansion, (3) the association 'external ornamentation of the plasma membrane + cortical microtubules', (4) the field of cortical microtubules and its number, (5) the location of the external ornamentation, (6) the location of the maximum number of cortical microtubules and (7) the number of mitochondria. We also outline the most interesting features for phylogenetic inference and their possible value in the context of digenean systematics, phylogeny and evolution. Associations between sperm models and superfamilies were found as follows: Type 1 in the Schistosomatoidea; Type 2 in the Hemiuroidea; Type 3 in the Opecoeloidea, Lepocreadioidea, Haploporoidea and Opisthorchioidea; Type 4 in the Gorgoderoidea, Microphalloidea, Plagiorchioidea and Gymnophalloidea; Type 5 in the Echinostomatoidea, Microscaphidioidea, Paramphistomoidea, Pronocephaloidea and Brachylaimoidea.

Spermatozoon ultrastructure in two monorchiid digeneans

Spermatological characteristics of species from two monorchiid genera, Opisthomonorchis and Paramonorcheides, have been investigated, for the first time, by means of transmission electron microscopy. The ultrastructural study reveals that the mature spermatozoon of Opisthomonorchis dinema and Paramonorcheides selaris share several characters such as the presence of two axonemes of different lengths showing the 9+"1" pattern of the Trepaxonemata, a nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies, granules of glycogen and similar morphologies of the anterior and posterior extremities. The slight differences between the male gamete of O. dinema and P. selaris are the length of the first axoneme and the position of the second mitochondrion. This study also elucidates the general morphology of the spermatozoon in all monorchiid species described so far, which corresponds to a unique spermatozoon type. Other interesting finds concern the spermatological similarities between monorchiid spermatozoa and the mature spermatozoon reported in the apocreadiid Neoapocreadium chabaudi. These similarities allow us to suggest a close phylogenetical relationship between the Monorchiidae and the Apocreadiidae, although more studies are needed, especially in the unexplored taxa.

First spermatological study in the Atractotrematidae (Digenea, Haploporoidea): the case of Atractotrema sigani, intestinal parasite of Siganus lineatus

The ultrastructural organization of the mature spermatozoon of the digenean Atractotrema sigani (from Siganus lineatus off New Caledonia) was investigated by transmission electron microscopy. The male gamete of A. sigani exhibits the general morphology described in digeneans with the presence of two axonemes of different lengths showing the 9 + “1” pattern of the Trepaxonemata, a nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation, spine-like bodies and granules of glycogen. However, the mature spermatozoon of A. sigani has some specific characters such as the morphology of its anterior region and the submembranous electron-dense material. Although similar structures have been reported in some digenean species, the presence of a submembranous electron-dense material describing a complete ring is reported here for the first time in the mature spermatozoon of A. sigani. In addition, sperm characteristics are compared between the Haploporoidea and their supposed close superfamilies, and possible phylogenetic implications of these findings for the Digenea are discussed.

Neomultitestis aspidogastriformis Bray and Cribb, 2003 (Digenea, Lepocreadiidae): mature spermatozoon and sperm morphologies in the Lepocreadioidea

Spermatological characteristics are described for the first time in the genus Neomultitestis Machida, 1982, belonging to the family Lepocreadiidae Odhner, 1905. Adult Neomultitestis aspidogastriformis were collected from the digestive tract of Platax teira, caught off New Caledonia. The mature spermatozoon of N. aspidogastriformis is described by transmission electron microscopy (TEM). It includes two axonemes with 9 + "1" pattern of Trepaxonemata, an antero-lateral electron-dense material, attachment zones, two mitochondria, a nucleus, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies, and granules of glycogen. Certain ultrastructural characteristics of the spermatozoon, especially the antero-lateral electron-dense material, are shared by N. aspidogastriformis and all species of the superfamily Lepocreadioidea studied so far. The antero-lateral electron-dense material, present in different families of lepocreadioids, supports the monophyletic status of the superfamily. We also list several ultrastructural characteristics which characterize the mature spermatozoon of the Lepocreadioidea.

Ultrastructural study of sperm cells in Acanthocolpidae: the case of Stephanostomum murielae and Stephanostomoides tenuis (Digenea)

The mature spermatozoa of Stephanostomum murielae and Stephanostomoides tenuis are described by transmission electron microscopy. They present several ultrastructural features previously reported in other digeneans. Their spermatozoa possess two axonemes of different length showing the 9 + '1' trepaxonematan pattern, four attachment zones, two mitochondria (with an anterior moniliform one in S. murielae), a nucleus, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies and granules of glycogen. The main differences between the mature spermatozoon of S. murielae and S. tenuis are the maximum number of cortical microtubules, the morphology of the anterior spermatozoon extremity and the anterior mitochondrion. This study is the first concerning members of the family Acanthocolpidae. The main ultrastructural characteristics discussed are the morphology of the anterior and posterior spermatozoon extremities, antero-lateral electron dense material, external ornamentations, spine-like bodies and number and morphology of mitochondria. In addition, the phylogenetic significance of all these ultrastructural features is discussed and compared to molecular results in order to highlight the complex relationships in the Digenea.

Collyricloides massanae (Digenea, Collyriclidae): spermatozoon ultrastructure and phylogenetic importance

The spermatological characteristics of Collyricloides massanae (Digenea: Collyriclidae), a parasite of Apodemus sylvaticus caught in France, were studied by means of transmission electron microscopy. The mature sperm of C. massanae presents two axonemes of different lengths with the 9 + “1” pattern of the Trepaxonemata, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies, one mitochondrion, a nucleus and granules of glycogen. An analysis of spermatological organisation emphasised some differences between the mature spermatozoon of C. massanae and those reported in the Gorgoderoidea species studied to date, specially belonging to the families Dicrocoeliidae, Paragonimidae and Troglotrematidae. The ultrastructural criteria described in C. massanae such as the morphology of both anterior and posterior spermatozoon extremities, the association “external ornamentation + cortical microtubules”, the type 2 of external ornamentation and the spine-like bodies would allow us to bring closer the Collyriclidae to Microphalloidea. However, further ultrastructural and molecular studies are needed particularly in the unexplored taxa in order to fully resolve the phylogenetic position of the Collyriclidae.

Spermatological characteristics of Pleurogenidae (Digenea) inferred from the ultrastructural study of Pleurogenes claviger, Pleurogenoides medians and Prosotocus confusus

The present work constitutes the first ultrastructural analysis of the spermatozoon in the Pleurogenidae, with the study of three species belonging to three of the 16 genera included in this family, namely Pleurogenes claviger, Pleurogenoides medians and Prosotocus confusus. The mature spermatozoa of these pleurogenids present two axonemes of the 9+“1” trepaxonematan pattern, a nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation, spine-like bodies and granules of glycogen. The organization of these characters in the sperm cell is similar in the three species. Thus, the anterior spermatozoon extremity is filiform and a continuous and submembranous layer of parallel cortical microtubules surrounds the axonemes at their anterior end. The posterior spermatozoon extremity exhibits the second axoneme and corresponds to the Cryptogonimidean type of Quilichini et al. (2010). Slight differences were noted between the spermatozoon of P. confusus and those of the two remaining species in the location of mitochondria.

Spermatological characteristics of Elstia stossichianum (Digenea, Mesometridae) from the intestine of the cow bream (Sarpa salpa) off Dakar, Senegal

The current study was designed to increase the spermatological ultrastructural database on Digenea, thus contributing to the future establishment of phylogenetic relationships within this group based on ultrastructural characteristics of both spermiogenesis and spermatozoa. Spermiogenesis in Elstia stossichianum begins with the formation of a differentiation zone containing two centrioles, two striated rootlets, a nucleus, several mitochondria and an intercentriolar body constituted by seven electron-dense layers. Each centriole develops into a free flagellum growing orthogonally to the median cytoplasmic process. Proximo-distal fusion of the flagella with the median cytoplasmic process occurs after flagellar rotation. Both nucleus and mitochondria migrate before the complete proximo-distal fusion of both flagella with the median cytoplasmic process. Finally, the constriction of the ring of arched membranes gives rise to the young spermatozoon. The mature spermatozoon of E. stossichianum exhibits two axonemes of different length of the 9+‘1’ trepaxonematan pattern, a nucleus, a mitochondrion, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, a lateral expansion, spine-like bodies, cytoplasmic ornamented buttons and granules of glycogen. The formation of cytoplasmic ornamented buttons during the final stages of spermiogenesis is reported here for the first time.