Spermatozoon ultrastructure and spermiogenesis are significant characters for phylogenetic inference. Sperm ultrastructure is reviewed from the literature in 56 species of Eucestoda. Data are available for 11 of the 12 orders of Eucestoda (Lecanicephalidea excepted), but in some orders data are scarce and often limited to a single species. Spermiogenesis and sperm ultrastructure in the Eucestoda is compared to that of other parasitic Platyhelminthes, with emphasis on structures of phylogenetic interest. Not only the descriptions of sperm structure, but those of the process of spermiogenesis, are necessary to define characters. Synapomorphies based on sperm ultrastructure for the Eucestoda include the absence of a mitochondrion in mature sperm and the presence of a crested body. A proposed synapomorphy for the Cyclophyllidea + Tetrabothriidea is the twisting of the peripheral microtubules; the absence of intercentriolar body and the absence of striated roots in the spermatid may constitute additional synapomorphies for this assemblage. Absence of flagellar rotation during spermiogenesis is synapomorphic for the Cyclophyllidea, and absence of proximodistal fusion could be synapomorphic for a part of the Cyclophyllidea. Several other characters could be useful for understanding phylogeny within the Eucestoda. The polarity of these characters could in several cases be determined, but diagnoses for taxa or relationships based on synapomorphies cannot be specified unequivocally due to putative convergence. Such characters and their putative polarity include: (1) the number of axonemes in mature spermatozoon (plesiomorphic=2; apomorphic=1); (2) size and number of crested bodies (p=1; a=several); and (3) angle of twisted microtubules; shape of nucleus (p=compact cord; a=crescent and annulus). Additional apomorphic attributes include (1) presence of a periaxonemal sheath (a putative synapomorphy for the Cyclophyllidea + Tetrabothriidea if reversals are postulated in certain cyclophyllideans); (2) presence of proteinaceous transverse walls; (3) presence of dense granules; and (4) shape of apical cones and posterior structures. Studies of sperm structure in the poorly known orders and additional comparative studies in the Cyclophyllidea are expected to provide new information for elucidation of phylogenetic relationships.

Species of Pseudorhabdosynochus were studied from fresh specimens collected from Epinephelus fasciatus and E. merra off New Caledonia, South Pacific, and specimens deposited in Museums. Experiments on two species demonstrated that the sclerotised hollow organs, such as the quadriloculate male copulatory organ and the vagina, may show differences in measurements of up to 50% when flattened. P. caledonicus n. sp. is described from E. fasciatus in New Caledonia, on which it is relatively rare; it is distinguished on the basis of the quadriloculate organ, which has a very thin anterior wall, the sclerotised parts of the vagina in form of a straight tube with a star-shaped lateral structure, and the squamodiscs composed of 11 open rows of rodlets. P. cupatus (Young, 1969) is redescribed from abundant material from E. fasciatus off New Caledonia (new geographical record) and compared with paratype specimens from Australia (from E. fasciatus and E. merra) and specimens from E. fasciatus in the Red Sea (both herein redescribed and figured); a specimen was also found on a slide from E. merra off Vanuatu. P. melanesiensis (Laird, 1958) is redescribed from material from E. merra off New Caledonia (new geographical record) and compared with type-specimens (herein redescribed and figured) from the same host off Vanuatu. The structure of the sclerotised vagina in P. cupatus and P. melanesiensis is very similar, with a thin-walled tube and a heavily sclerotised structure with three loculi. P. vagampullum (Young, 1969) is redescribed from the paratypes from E. merra from Australia, but was not found in New Caledonia; specimens included among its paratypes (from E. merra in Australia), but different, are herein attributed to Pseudorhabdosynochus sp. 3. P. lantauensis (Beverley-Burton & Suriano, 1981) is redescribed from the paratype specimens from E. longispinis off Hong-Kong. A specimen found among the paratypes of P. cupatus belongs to a different species, herein designated as Pseudorhabdosynochus sp. 1. Specimens from E. longispinis off Hong-Kong, previously attributed to P. cupatus, are attributed to another species, Pseudorhabdosynochus sp. 2. The three species P. cupatus, Pseudorhabdosynochus sp. 1 and Pseudorhabdosynochus sp. 2 have in common a 'lamellosquamodisc' composed of central telescopic lamellae and peripheral rows of rodlets; they can be distinguished by the shape of the sclerotised vagina and measurements of the haptoral hard-parts. Specimens from E. longispinis off Hong-Kong, previously attributed to P. vagampullum, probably belong to a different species. Consequently, after these modified determinations, P. cupatus parasitises only E. fasciatus and E. merra, and P. melanesiensis and P. vagampullum parasitise only E. merra. With their wide geographical distribution and different species of Pseudorhabdosynochus in different localities, E. fasciatus and E. merra appear to represent excellent models for investigating monogenean biogeography in the Indo-Pacific Ocean.

The phylogeny of the Eucestoda was evaluated based on a suite of 49 binary and multistate characters derived from comparative morphological and ontogenetic studies; attributes of adult and larval tapeworms were considered. A single most parsimonious tree (MPT) (consistency index = 0.872; retention index = 0.838; and homoplasy index = 0.527) was fully resolved and is specified by the following: (Gyrocotylidea, (Amphilinidea, ((Spathebothriidea, (Pseudophyllidea, ((Diphyllidea, (Trypanorhyncha, (Tetraphyllidea, (Lecanicephalidea, ((Nippotaeniidea, (Tetrabothriidea, Cyclophyllidea)), Proteocephalidea))))), Haplobothriidea))), Caryophyllidea))). Monophyly for the Eucestoda was firmly corroborated. Trees derived from the primary and bootstrap analyses were congruent, but low values, particularly for relationships among the tetrafossate tapeworms, indicated additional examination is warranted. The MPT was found to be the most efficient hypothesis for describing character evolution and in specifying relationships among the orders when compared to those concepts that had been developed for the tapeworms over the past century. Areas of congruence were shared among the current hypothesis and one or more of the prior hypotheses. Major conclusions include: (1) Caryophyllidea are basal and monozooy is ancestral; (2) difossate forms are primitive, and the Pseudophyllidea are the sister group of the strongly polyzoic tapeworms; (3) Nippotaeniidea are highly derived; (4) the higher tapeworms (Tetraphyllidea, Lecanicephalidea, Proteocephalidea, Nippotaeniidea, Tetrabothriidea, and Cyclophyllidea) are closely related or potentially coordinate groups: (5) Tetrabothriidea and the Cyclophyllidea are sister groups; and (6) Tetraphyllidea is paraphyletic, with the Onchobothriidae basal to the Phyllobothriidae. Character support for placement of the Tetrabothriidea continues to be contradictory, and this order may represent a key to understanding the phylogeny of the higher cestodes. The current study constitutes a complete historical review and poses a new and robust hypothesis for the phylogeny of the Eucestoda.

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Recent cladistic phylogenies of the Platyhelminthes, especially the parasitic species, use for synapomorphies several characters of the spermatozoa, together with other characters. This paper reinvestigates synapomorphies based on sperm characteristics. The outgroup usually chosen for such studies on the parasitic Platyhelminthes (Cercomeria) is the "Dalyelliida" or "Dalyellioida," generally considered a paraphyletic group, but sperm structure in this group shows great variation. In this paper, the Typhloplanoida, which have a plesiomorphic structure (two free axonemes), are considered the outgroup. One of the synapomorphies recently proposed for the Neodermata is "spermatozoon with axonemes incorporated in the cytoplasm." This definition introduces convergences with several other groups of nonparasitic Platyhelminthes. A more precise definition of spermiogenesis, based on a detailed description, is proposed in this paper and avoids homoplasies: "proximodistal fusion of the axonemes." This implies the presence of dorsal and ventral microtubules in the nuclear region of the spermatozoon. This synapomorphy characterizes the Cercomeridea but not the Neodermata (= Udonellidea + Cercomeridea). The character "absence of dense granules in the spermatozoon" should be considered a synapomorphy for the Neodermata and has almost no homoplasies. For the Temnocephalidea, the spiral pattern of the peripheral microtubule row is proposed as a synapomorphy. This character is present in Didymorchis; however, Didymorchis lacks tentacles, which are present in the other genera, and thus the ultrastructural synapomorphy is in conflict with a recently proposed morphological synapomorphy for this group: the presence of tentacles. No synapomorphy of the spermatozoon can be proposed for the Monogenea, but the presence of lateral microtubules lining the axonemes is proposed as a synapomorphy for the polyopisthocotylean Monogenea, and the absence of dorsal and lateral microtubules is proposed as a synapomorphy for the monopisthocotylean Monogenea (this is a reversal of the synapomorphy for the Cercomeridea defined above). The cyclophyllidean Eucestoda show a twisting of the peripheral microtubules of the spermatozoon, which is proposed as a synapomorphy.

Coral reefs are known for their high level of biodiversity, but parasite biodiversity has not been evaluated. Cases such as Epinephelus maculatus, described here, show that the numerical estimation of parasite biodiversity in coral reefs could reach more than ten times the number of fish species; consequently, the extinction of certain fish species from endangered coral reefs would result in the co-extinction of at least ten times the number of parasite species. E. maculatus is a grouper of intermediate size (1-2 kg) and common in the coral reefs of New Caledonia, South Pacific. Based on the examination of more than 800 monogenean specimens, 12 species of monogeneans (ten diplectanids and two ancyrocephalids) were differentiated on the gills. These species of diplectanids have not been found in other epinephelines in the same area and thus are considered as specific to this host. In addition, three species of copepods, and isopod larvae, are present on the gills; E. maculatus thus has a total of 16 species of gill ectoparasites, which can be found together on a single individual fish. Diplectanids include Laticola dae Journo & Justine, 2006, which is the most abundant species representing about 50% of the specimens, and nine species which are rare, each representing 2-7% of the specimens: Diplectanum uitoe n. sp. and eight species of Pseudorhabdosynochus Yamaguti, 1958. D. uitoe, provisionally attributed to Diplectanum Diesing, 1858, is characterised by a small conical penis with internal walls. Pseudorhabdosynochus auitoe n. sp., P. buitoe n. sp., P. cuitoe n. sp., P. duitoe n. sp., P. euitoe n. sp. and P. fuitoe n. sp. are differentiated on the basis of the morphology of the sclerotised vagina, but are very similar in other characteristics; P. guitoe n. sp. is characterised by a quadriloculate organ with very thick walls and a very small sclerotised vagina; and P. huitoe n. sp. is characterised by its sclerotised vagina and by very long ventral and dorsal haptoral bars. Two rare (2-3% of specimens) ancyrocephalids, Haliotrema epinepheli Young, 1969 and Haliotrema sp., are briefly described in relation to the male copulatory organs and haptoral bars; H. epinepheli is apparently a generalist species found in various epinephelines and other fish species. A table of the 50 species of diplectanids (Pseudorhabdosynochus, Laticola Yang et al., 2006, Echinoplectanum Justine & Euzet, 2006 and Diplectanum) from serranids is provided.

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The ultrastructure of the mature spermatozoon of Gyliauchen sp., a parasite of the dusky rabbitfish Siganus fuscescens, was studied by transmission electron microscopy. The spermatozoon possesses two axonemes of the 9+"1" pattern of Trepaxonemata, four attachment zones, one mitochondrion, a nucleus, cortical microtubules, external ornamentation of the plasma membrane, and spine-like bodies. The main characteristics of this spermatozoon are the presence of one mitochondrion, spine-like bodies not associated with the external ornamentation, and a posterior extremity of type 3 that is characterized by the following sequence: posterior extremity of the nucleus then posterior extremity of the second axoneme. Numerous other ultrastructural features are also discussed and compared to the digenean spermatology literature. This is the first study of a member of the Gyliauchenidae and the fourth within the Lepocreadioidea. The results show that many ultrastructural characters are variable within this superfamily and could be useful for phylogeny.