An investigation of the co-evolutionary relationships between onchobothriid tapeworms and their elasmobranch hosts

Determinants of diversity and composition of the tapeworm fauna of blue sharks, Prionace glauca: a geographical and host-specificity analysis

Blue sharks, Prionace glauca, are cosmopolitan, extremely vagile sharks and the species among elasmobranchs for which most surveys containing tapeworm community data are available worldwide. In this study we report on the tapeworm fauna of three samples of blue sharks (n = 37) from two new regions (one sample from Galicia, north-east Atlantic, and two from Valencia, western Mediterranean), and compared it with previous studies, assessing the relative role of the ecological and evolutionary factors in structuring local tapeworm assemblages. Nine cestode taxa were identified, of which four included adult specimens, that is, Platybothrium auriculatum, Prosobothrium armigerum, Anthobothrium caseyi and Molicola horridus. The abundance of these species, and Brillouin's diversity index, differed significantly among samples without a clear geographical signal. A comparison with six previous surveys revealed that tapeworm assemblages were composed of the same 'core' taxa, with mean species richness typically ranging from two to four species. Global records of adult tapeworms in blue sharks included: 15 taxa identified at species level, of which only eight (generalist trypanorhynchs) were shared with other sympatric host species; five mostly with other carcharhinids; and three with large lamnid sharks sharing the blue sharks' habitat. The composition of tapeworm communities of blue sharks is thus highly constrained by strong host specificity, with composition and abundance varying across localities depending on idiosyncratic environmental conditions.

Threatened, host-specific affiliates of a red-listed host: Three new species of Acanthobothrium van Beneden, 1849 (Cestoda: Onchoproteocephalidea) from the endangered white skate, Rostroraja alba (Lacépède)

The white skate, Rostroraja alba (Lacépède), is listed as an endangered species, the second-highest category before being declared extinct in the wild, in the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species. This species is heavily affected by anthropogenic impacts such as capture induced stress by overfishing and by-catch, habitat degradation and pollution that caused a drastic decline in populations in recent years. As part of a larger study on elasmobranch affiliates in southern Africa, two specimens of R. alba were screened. Three species of the tapeworm genus Acanthobothrium van Beneden, 1849 (Cestoda: Onchoproteocephalidea) were discovered. Application of Ghoshroy and Caira's classification system facilitated the differentiation of congeners through a combination of specific morphological characteristics. As a consequence, three species new to science are described herein, namely Acanthobothrium umbungus n. sp., Acanthobothrium usengozinius n. sp., and Acanthobothrium ulondolozus n. sp. In light of these new discoveries from an endangered host, it is apparent to address the conservation status of its affiliate species, that co-evolved with their elasmobranch hosts for millions of years, thereby creating unique and intimate host-parasite interrelationships. Currently, altering environmental conditions caused by anthropogenic pressures have direct impacts on this host-parasite system with increasing risks of extinction. As merely 9% of elasmobranchs in South African waters have been examined for endohelminths and other affiliate taxa, extensive studies on these organisms and their hosts implementing multisource approaches are needed. This will provide a better understanding on the intimate nature of host-parasite systems that may lead to new prospects in conservation science and the preservation of threatened host species, such as R. alba, together with their unique fauna of affiliate species.

•

Three new species of Acanthobothrium were discovered in the endangered white skate, Rostroraja alba, off the coast of South Africa.

•

The three species described (A. umbungus n. sp., A. usengozinius n. sp., and A. ulondolozus n. sp.) display merely a single cestode genus among the hidden diversity of species from elasmobranchs.

•

The current increase in threatened free-living host species results in an even greater loss in affiliate species that remain unknown and scientifically underexplored.

•

Assessing the status and incorporating affiliate species (i.e. cestodes) into novel conservation schemes may contribute to the conservation of threatened host species and marine populations worldwide, which, in turn, will protect affiliate species as vital “key players” for host species and entire ecosystems.

Morphological updates, host-specificity, molecular data and phylogenetic analysis of Acanthobothrium coronatum (Cestoda: Onchoproteocephalidea), a neglected parasite of the nursehound Scyliorhinus stellaris

Acanthobothrium is the most speciose genus of onchoproteocephalidean cestodes, whose adults parasitize the intestine of elasmobranch fishes. Acanthobothrium coronatum, the type species of the genus described from Mediterranean elasmobranchs, remains a little known parasite, with the most recent reports dating back to the fifties. We hereby investigate host-specificity and redescribe A. coronatum from the same locality of its original description by using light and scanning electron microscopy approaches. Moreover, molecular and phylogenetic data inferred from the analysis of the 28S rDNA gene are reported for the first time. Out of the nine elasmobranch species examined from Gulf of Naples, we only detected A. coronatum in the intestine of Scyliorhinus stellaris, with infection patterns that supports evident host-specificity for this shark species. The genetic characterization of 28S rDNA showed 99.8-100% similarity with larvae previously found in Octopus vulgaris from the same area investigated here. Conspecificity between the present material and the larvae found in the octopus was also confirmed by the tree topology. The host-parasite phylogeny is discussed, even if additional molecular data are needed to clarify potential host-parasite patterns. Notwithstanding this limitation, this is the first molecular study revealing conspecificity between an adult Acanthobothrium species from a shark and the larvae found in an intermediate/paratenic host, shedding light on the transmission pathway of A. coronatum in S. stellaris. Finally, the taxonomic, molecular, and phylogenetic data presented here allow a better characterization of a neglected parasite.

Role of ecology and phylogeny in determining tapeworm assemblages in skates (Rajiformes)

An understanding of the mechanisms that determine host and parasite relationships is a central aim in parasitology. Association of a parasite species with a host species may be influenced primarily by phylogenetic constraints that cause parasite species to co-speciate with their host species, or predominantly by ecological parameters that influence all other co-evolutionary scenarios. This study aimed to investigate the role of co-speciation as well as other co-evolutionary scenarios in influencing the assemblages of tapeworm parasites (marine cestodes) in skate hosts (Rajiformes) using a modification of the PACo (Procrustean Approach to Cophylogeny) method. The study found that phylogeny and host ecology are both significant predictors of skate-tapeworm relationships, implying that co-speciation as well as other co-evolutionary scenarios are shaping these associations. The study also investigated the key ecological parameters influencing host-switching and found that host diet, distribution depth, average body size and geographical location have a combined effect. Given the importance of parasites in ensuring healthy and stable marine ecosystems, the findings of this study have implications for conservation management worldwide.

Systematics and diversification of Anindobothrium Marques, Brooks & Lasso, 2001 (Eucestoda: Rhinebothriidea)

Tapeworms of the genus Anindobothrium Marques, Brooks & Lasso, 2001 are found in both marine and Neotropical freshwater stingrays of the family Potamotrygonidae. The patterns of host association within the genus support the most recent hypothesis about the history of diversification of potamotrygonids, which suggests that the ancestor of freshwater lineages of the Potamotrygonidae colonized South American river systems through marine incursion events. Despite the relevance of the genus Anindobothrium to understand the history of colonization and diversification of potamotrygonids, no additional efforts were done to better investigate the phylogenetic relationship of this taxon with other lineages of cestodes since its erection. This study is a result of recent collecting efforts to sample members of the genus in marine and freshwater potamotrygonids that enabled the most extensive documentation of the fauna of Anindobothrium parasitizing species of Styracura de Carvalho, Loboda & da Silva, Potamotrygon schroederi Fernández-Yépez, P. orbignyi (Castelnau) and P. yepezi Castex & Castello from six different countries, representing the eastern Pacific Ocean, Caribbean Sea, and river basins in South America (Rio Negro, Orinoco, and Maracaibo). The newly collected material provided additional specimens for morphological studies and molecular samples for subsequent phylogenetic analyses that allowed us to address the phylogenetic position of Anindobothrium and provide molecular and morphological evidence to recognize two additional species for the genus. The taxonomic actions that followed our analyses included the proposition of a new family, Anindobothriidae fam. n., to accommodate the genus Anindobothrium in the order Rhinebothriidea Healy, Caira, Jensen, Webster & Littlewood, 2009 and the description of two new species-one from the eastern Pacific Ocean, A. carrioni sp. n., and the other from the Caribbean Sea, A. inexpectatum sp. n. In addition, we also present a redescription of the type species of the genus, A. anacolum (Brooks, 1977) Marques, Brooks & Lasso, 2001, and of A. lisae Marques, Brooks & Lasso, 2001. Finally, we discuss the paleogeographical events mostly linked with the diversification of the genus and the protocols adopted to uncover cryptic diversity in Anindobothrium.

A new genus of rhinebothriidean cestodes from batoid elasmobranchs, with the description of five new species and two new combinations

Survey work of batoid elasmobranchs in the eastern Atlantic and Indo-Pacific revealed multiple species of a new genus of cestode. Stillabothrium Healy et Reyda gen. n. (Rhinebothriidea: Escherbothriidae) is unique in its possession of an even number of non-medial longitudinal septa in the posterior portion of the bothridia, resulting in a series of loculi that are longer than wide (i.e. vertically oriented) and are arranged in columns. Five new species of Stillabothrium are described, S. ashleyae Willsey et Reyda sp. n., S. davidcynthiaorum Daigler et Reyda sp. n., S. campbelli Delgado, Dedrick et Reyda sp. n., S. hyphantoseptum Herzog, Bergman et Reyda sp. n., S. jeanfortiae Forti, Aprill et Reyda sp. n., and two species are formally transferred to the genus, S. amuletum (Butler, 1987) comb. n., and S. cadenati (Euzet, 1954) comb. n., the latter of which is redescribed. The species differ in the configuration of the other bothridial septa and in proglottid anatomy. Species of Stillabothrium were found parasitising a total of 17 species of batoid elasmobranchs of the genera Dasyatis Rafinesque, Glaucostegus Bonaparte, Himantura Müller et Henle, Pastinachus Rüppell, Rhinobatos Linck and Zanobatus Garman, including several host species that are likely new to science. A phylogenetic hypothesis based on Bayesian analysis of 1 084 aligned positions of the D1-D3 region of 28S rDNA for 27 specimens representing 10 species of Stillabothrium and two outgroup species supported the monophyly of Stillabothrium. These results also supported morphologically determined species boundaries in all cases in which more than one specimen of a putative species was included in the analysis. Host specificity appears to vary across species of Stillabothrium, with the number of host species parasitised by each species of Stillabothrium ranging from one to four. The geographic distribution of species of Stillabothrium spans the eastern Hemisphere, including the eastern Atlantic (coastal Senegal) and several locations in the Indo-Pacific (coastal Vietnam, Borneo and Australia). In addition, Phyllobothrium biacetabulatum Yamaguti, 1960 is formally transferred into family Escherbothriidae, although its generic placement remains uncertain (species incertae sedis).

Szidat's rule re-tested: relationships between flea and host phylogenetic clade ranks in four biogeographic realms

We tested Szidat's rule (the more primitive the host, the more primitive the parasites it harbours) by analysing the relationships between phylogenetic clade ranks of fleas and their small mammalian hosts in four biogeographic realms (Afrotropics, Neotropics, Nearctic and Palearctic). From the host perspective, we tested the association between host clade rank and the mean clade rank of all fleas collected from this host. From the flea perspective, we tested the relationships between flea clade rank and the mean clade rank of hosts on which this flea was recorded. First, we tested whether the analysis of the relationships between host and flea clade ranks should be controlled for phylogenetic dependence among either host or flea species. Then, we tested for the associations between host and flea clade ranks separately for each realm using either a phylogenetic general least-squares analysis or an ordinary least-squares analysis. In all realms, the mean clade rank of fleas parasitic on a given host increased with an increase of this host's clade rank, and the mean clade rank of hosts recorded on a given flea increased with an increase of this flea's clade rank, suggesting that Szidat's rule, at least to some extent, holds for fleas.

Do the historical biogeography and evolutionary history of the digenean Margotrema spp. across central Mexico mirror those of their freshwater fish hosts (Goodeinae)?

Host-parasite systems provide an ideal platform to study evolution at different levels, including codivergence in a historical biogeography context. In this study we aim to describe biogeographic and codivergent patterns and associated processes of the Goodeinae freshwater fish and their digenean parasite (Margotrema spp.) over the last 6.5 Ma (million years), identifying the main factors (host and/or hydrogeomorphology) that influenced the evolution of Margotrema. We obtained a species tree for Margotrema spp. using DNA sequence data from mitochondrial and nuclear molecular markers (COI and ITS1, respectively) and performed molecular dating to discern divergence events within the genus. The dispersal-extinction-cladogenesis (DEC) model was used to describe the historical biogeography of digeneans and applied to cophylogenetic analyses of Margotrema and their goodeine hosts. Our results showed that the evolutionary history of Margotrema has been shaped in close association with its geographic context, especially with the geological history of central Mexico during the Pleistocene. Host-specificity has been established at three levels of historical association: a) Species-Species, represented by Xenotaenia resolanae-M. resolanae exclusively found in the Cuzalapa River Basin; b) Species-Lineage, represented by Characodon audax-M. bravoae Lineage II, exclusive to the Upper and Middle Mezquital River Basin, and c) Tribe-Lineage, including two instances of historical associations among parasites and hosts at the taxonomical level of tribe, one represented by Ilyodontini-M. bravoae Lineage I (distributed across the Ayuquila and Balsas River Basins), and another comprised of Girardinichthyini/Chapalichthyini-M. bravoae Lineage III, found only in the Lerma River Basin. We show that the evolutionary history of the parasites is, on several occasions, in agreement with the phylogenetic and biogeographic history of their hosts. A series of biogeographic and host-parasite events explain the codivergence patterns observed, in which cospeciation and colonisation via host-switching and vicariant plus dispersal events are appreciated, at different times during the diversification history of both associates, particularly during the Pleistocene.

A review of molecular approaches for investigating patterns of coevolution in marine host-parasite relationships

Parasites and their relationships with hosts play a crucial role in the evolutionary pathways of every living organism. One method of investigating host-parasite systems is using a molecular approach. This is particularly important as analyses based solely on morphology or laboratory studies of parasites and their hosts do not take into account historical evolutionary interactions that can shape the distribution, abundance and population structure of parasites and their hosts. However, the predominant host-parasite coevolution literature has focused on terrestrial hosts and their parasites, and there still is a lack of studies in marine environments. Given that marine systems are generally more open than terrestrial ones, they provide fascinating opportunities for large-scale (as well as small-scale) geographic studies. Further, patterns and processes of genetic structuring and systematics are becoming more available across many different taxa (but especially fishes) in many marine systems, providing an excellent basis for examining whether parasites follow host population/species structure. In this chapter, we first highlight the factors and processes that challenge our ability to interpret evolutionary patterns of coevolution of hosts and their parasites in marine systems at different spatial, temporal and taxonomic scales. We then review the use of the most commonly utilized genetic markers in studying marine host-parasite systems. We give an overview and discuss which molecular methodologies resolve evolutionary relationships best and also discuss the applicability of new approaches, such as next-generation sequencing and studies utilizing functional markers to gain insights into more contemporary processes shaping host-parasite relationships.

Diversification and species boundaries of Rhinebothrium (Cestoda; Rhinebothriidea) in South American freshwater stingrays (Batoidea; Potamotrygonidae)

BACKGROUND

Neotropical freshwater stingrays (Batoidea: Potamotrygonidae) host a diverse parasite fauna, including cestodes. Both cestodes and their stingray hosts are marine-derived, but the taxonomy of this host/parasite system is poorly understood.

METHODOLOGY

Morphological and molecular (Cytochrome oxidase I) data were used to investigate diversity in freshwater lineages of the cestode genus Rhinebothrium Linton, 1890. Results were based on a phylogenetic hypothesis for 74 COI sequences and morphological analysis of over 400 specimens. Cestodes studied were obtained from 888 individual potamotrygonids, representing 14 recognized and 18 potentially undescribed species from most river systems of South America.

RESULTS

Morphological species boundaries were based mainly on microthrix characters observed with scanning electron microscopy, and were supported by COI data. Four species were recognized, including two redescribed (Rhinebothrium copianullum and R. paratrygoni), and two newly described (R. brooksi n. sp. and R. fulbrighti n. sp.). Rhinebothrium paranaensis Menoret & Ivanov, 2009 is considered a junior synonym of R. paratrygoni because the morphological features of the two species overlap substantially. The diagnosis of Rhinebothrium Linton, 1890 is emended to accommodate the presence of marginal longitudinal septa observed in R. copianullum and R. brooksi n. sp. Patterns of host specificity and distribution ranged from use of few host species in few river basins, to use of as many as eight host species in multiple river basins.

SIGNIFICANCE

The level of intra-specific morphological variation observed in features such as total length and number of proglottids is unparalleled among other elasmobranch cestodes. This is attributed to the large representation of host and biogeographical samples. It is unclear whether the intra-specific morphological variation observed is unique to this freshwater system. Nonetheless, caution is urged when using morphological discontinuities to delimit elasmobranch cestode species because the amount of variation encountered is highly dependent on sample size and/or biogeographical representation.

Synergy advances parasite taxonomy and systematics: an example from elasmobranch tapeworms

The synergism facilitated by a series of recent developments has conspired to catalyze rapid advancements in the taxonomy and systematics of elasmobranch tapeworms. These developments are: (1) increased interest in global biodiversity; (2) globalization-facilitated communication; (3) enhanced microscopic and digital technologies; (4) availability of web-based taxonomic resources; (5) ease of use and low cost of molecular techniques and (6) the impressive repertoire of available phylogenetic methods. As a consequence, an estimation of global elasmobranch tapeworm diversity is now within our grasp, as is a basic understanding of the effort and resources required to complete the discovery and description of this fauna globally. The generation of robust hypotheses of the phylogenetic relationships for most elasmobranch-parasitizing cestode orders is also well underway. An international community of cestodologists has emerged and through their sharing of knowledge and specimens is making great strides towards expanding knowledge of the cestode fauna of vertebrates worldwide. It is important that these efforts continue to move forward in a collaborative fashion, integrating morphological and molecular data, but also fully engaging elasmobranch taxonomists and systematists. It is equally important that efforts to characterize and describe global biodiversity are not derailed by such seductive, but ultimately unrewarding impracticable initiatives as molecular taxonomy. Integrated taxonomy is certainly not for the feint of heart, but those with the courage to pursue this strategy will be responsible for maintaining and enhancing the biologically relevant context required for effective species recognition well into the future.

A new genus and two new species of Aporhynchidae (Cestoda: Trypanorhyncha) from catsharks (Carcharhiniformes: Scyliorhinidae) off Taiwan

New collections of cestodes from the spiral intestines of catsharks (Carcharhiniformes: Scyliorhinidae) off Taiwan have led to the discovery of a new genus and 2 new species of trypanorhynchs. These taxa are relatively unique among trypanorhynchs in their lack of all elements of the rhyncheal apparatus. The new genus, Nakayacestus n. gen., is considered to belong with Aporhynchus in the Aporhynchidae. In addition to lacking the rhyncheal apparatus, these 2 genera share circum-medullary vitelline follicles, post-ovarian testes, and complex terminal genitalia consisting of accessory, external, and internal seminal vesicles. The 2 genera differ conspicuously in spinithrix configuration; whereas both species of Nakayacestus n. gen. bear scolex spinitriches that are bifid, trifid, or pectinate, species of Aporhynchus either lack scolex spinitriches entirely or possess spathulate spinitriches. The configuration of the bothria of the 2 genera also differ conspicuously. Whereas the bothria of Aporhynchus are sessile and generally do not extend beyond the lateral margins of the cephalic peduncle, those of Nakayacestus bear only a tenuous connection with the scolex proper, being conspicuously free both anteriorly and posteriorly and extending conspicuously beyond the cephalic peduncle. Futhermore, the boundary between the scolex and the strobila of members of the new genus is clearly delineated, whereas this distinction is ill-defined in species of Aporhynchus. Nakayacestus takahashii n. sp., the type of the new genus, was collected from the Broadmouth catshark, Apristurus macrostomus, and differs from Nakayacestus tanyderus n. sp., collected from the Blacktip sawtail catshark, Galeus sauteri, in being shorter, bearing a longer pedunculus scolecis, an ovary that is more posterior in the proglottid, and fewer post-ovarian testes. Furthermore, the 2 new species differ conspicuously from one another in the configuration of their scolex spinitriches.

Evolution of interspecific variation in size of attachment structures in the large tapeworm genusAcanthobothrium(Tetraphyllidea: Onchobothriidae)

Parasites have evolved a myriad of attachment structures closely adapted to their hosts and sites of attachment. Here, using members of the genusAcanthobothriumvan Beneden, 1850 (Cestoda: Tetraphyllidea: Onchobothriidae), we (i) examined the influence of host body size and phylogeny, in addition to morphological features of these tapeworms, on the size of 3 structures used in attachment (bothridia, accessory suckers and hooks) by means of general linear models and phylogenetic-independent contrasts methods, and (ii) quantified the scaling exponents of relationships between size of attachment structures and tapeworm body size. Our results indicate that there exists a positive relationship, albeit not directly proportional, between size of attachment structures andAcanthobothriumspp. body size, and hook size and size of bothridia and accessory suckers. These results suggest that the resource investment in whole-body growth is greater than that in attachment structures, and that a greater investment in development of bothridia and accessory suckers is required to maintain an equivalent functional efficacy to hooks. In addition, host body size also influences, though less markedly, the size of attachment structures inAcanthobothriumspp. independently of parasite size itself.Acanthobothriumspecies have evolved a generalized mode of attachment that is successful in maintaining their position on various intestinal mucosal topographies across a variety of hosts exploiting different food resources.

Coevolution of Retrovarium n. gen. (Digenea: Cryptogonimidae) in Lutjanidae and Haemulidae (Perciformes) in the Indo-West Pacific

We describe 11 new species of cryptogonimids belonging to Retrovarium n. gen., from eight species of Lutjanidae and one species of Haemulidae, from the Great Barrier Reef, French Polynesia and the Maldives. We also transfer Neoparacryptogonimus saccatus (Manter, 1963) and Neoparacryptogonimus sphericus Nahhas, Sey & Nishimoto, 1998 to Retrovarium. The morphologically based taxonomic approach was augmented with DNA sequence data from three nuclear ribosomal DNA regions (28S, ITS1 and ITS2) to explore the species integrity, biogeographic distribution and evolution of the species recognised here. Sequencing included multiple replicates and revealed 11 distinct genotypes which corroborated our morphologically based hypotheses of putative species present in the system. There was no intraspecific variation and all three rDNA regions differed between every combination of species. Two species exhibited wide geographic ranges, having identical rDNA sequences between the Great Barrier Reef and the Maldives, localities separated by over 9600 km. One host species, Symphorus nematophorus, proved to be exceptionally rich, harbouring six species. Minimum evolution analyses were conducted on each of the rDNA datasets independently; minimum evolution, maximum likelihood and Bayesian inference analyses were conducted on a combined (28S, ITS1 and ITS2) dataset for sequence comparison purposes and to explore the evolutionary history of these parasites. To examine the coevolutionary history of this complex, assessment of phylogenetic relationships between the 23 species of Lutjanidae and two species of Haemulidae collected during this survey was performed with data from 16S and cytochrome b mtDNA using Bayesian inference analysis. Despite the high host specificity observed in most of the species, mapping of the parasites on the host phylogeny revealed an absence of strict coevolution or co-descent within this complex. Overall, Retrovarium appears to have had an exceptionally patchy radiation, failing to infect many taxa, infecting species with no readily discernible pattern, and radiating dramatically within one species.

A revision of Megalonchos Baer & Euzet, 1962 (Tetraphyllidea: Onchobothriidae), with the description of two new species and transfer of two species to Biloculuncus Nasin, Caira & Euzet, 1997

The onchobothriid tapeworm genus Megalonchos Baer & Euzet, 1962 is revised and the generic diagnosis amended based on the examination of some of Southwell's material of M. mandleyi (Southwell, 1927) Baer & Euzet, 1962, the type-specimens of M. dubius Prudhoe, 1969 and M. musteli Prudhoe, 1969, and material of two new species, M. sumansinghai n. sp. and M. shawae n. sp., collected from the snaggletooth shark Hemipristis elongatus off northern Australia. Based on their possession of two pairs of uni-pronged hooks (rather than one pair of bi-pronged hooks) and possession of, rather than lack of, post-vaginal testes, M. dubius and M. musteli are transferred to Biloculuncus Nasin, Caira & Euzet, 1997 as B. dubius (Prudhoe, 1969) n. comb. and B. musteli (Prudhoe, 1969) n. comb. Both new species of Megalonchos differ from M. mandleyi in their possession of conspicuously smaller hooks and shorter cephalic peduncles. The new species are readily distinguished from one another in that, whereas the pores of the axial prongs of the medial and lateral hooks are located well anterior to the middle of the prong in M. sumansinghai n. sp., they are well posterior to the middle of the prongs in M. shawae n. sp. In addition, the base of the lateral hook is longer relative to that of the medial hook in the latter species than it is in the former species. The proglottid anatomy of valid species of Megalonchos is described for the first time, and the lack of post-vaginal testes is confirmed for the genus. In addition, members of this genus appear to be characterised by a sacciform uterus that extends only to the level of the cirrus-sac and an ovary that is H-shaped in frontal view and bilobed in cross-section. Species of Megalonchos have now been reported from two of the eight known species of hemigaleid sharks.

Parasite histories and novel phylogenetic tools: Alternative approaches to inferring parasite evolution from molecular markers

Parasitological research is often contingent on the knowledge of the phylogeny/genealogy of the studied group. Although molecular phylogenetics has proved to be a powerful tool in such investigations, its application in the traditional fashion, based on a tree inference from the primary nucleotide sequences may, in many cases, be insufficient or even improper. These limitations are due to a number of factors, such as a scarcity/ambiguity of phylogenetic information in the sequences, an intricacy of gene relationships at low phylogenetic levels, or a lack of criteria when deciding among several competing coevolutionary scenarios. With respect to the importance of a precise and reliable phylogenetic background in many biological studies, attempts are being made to extend molecular phylogenetics with a variety of new data sources and methodologies. In this review, selected approaches potentially applicable to parasitological research are presented and their advantages as well as drawbacks are discussed. These issues include the usage of idiosyncratic markers (unique features with presumably low probability of homoplasy), such as insertion of mobile elements, gene rearrangements and secondary structure features; the problem of ancestral polymorphism and reticulate relationships at low phylogenetic levels; and the utility of a molecular clock to facilitate discrimination among alternative scenarios in host-parasite coevolution.

Phylogenetic relationships among monogenean gill parasites (Dactylogyridea, Ancyrocephalidae) infesting tilapiine hosts (Cichlidae): systematic and evolutionary implications

We studied the systematics of 14 species of monogenean (Ancyrocephalidae) gill parasites from West African tilapiine hosts (Cichlidae) using both morphological and genetic data. With these tools, we were able to: (i) confirm the validity of the previously described morphological parasite species and of the genus Scutogyrus; (ii) propose that some stenoxenous species (i.e., parasite species with more than one host) may be composed of sister species (e.g., Cichlidogyrus tilapiae); (iii) state that the use of the morphology of the haptoral sclerites is more suitable to infer phylogenetic relationships than the morphology of the genitalia (which seems to be more useful to resolve species-level identifications, presumably because of its faster rate of change). These results imply that: (i) the specificity of these monogenean parasites is greater than initially supposed (what were thought to be stenoxenous species may be assemblages of oïoxenous sister species); (ii) related species groups (i.e., "tilapiae," "halli," and "tiberianus") have to be, as genus Scutogyrus, validated within the 54 ancyrocephalid species described from 18 species of tilapiine hosts in West Africa, (iii) the group "tilapiae," due to its morphology and host range, have to be considered as being the most primitive; (iv) the occurrence of lateral transfers and parallel speciation processes are necessary to describe the repartition of the newly described parasite groups on the three host genera studied (Tilapia, Oreochromis, and Sarotherodon).

FIVE NEW SPECIES OF PEDIBOTHRIUM (TETRAPHYLLIDEA: ONCHOBOTHRIIDAE) FROM THE TAWNY NURSE SHARK, NEBRIUS FERRUGINEUS, IN THE PACIFIC OCEAN

The spiral intestines of 7 Tawny nurse sharks (Nebrius ferrugineus; Rhincodontidae) from Australia and French Polynesia were examined for tapeworms. These sharks hosted 5 new species of Pedibothrium. The 5 species were prepared for light and scanning electron microscopy. Whereas 3 of the species exhibit the bipronged hooks typical of members of Pedibothrium, 1 species was found to possess tiny unipronged hooks or to lack some, or all, hooks, and all individuals of the fifth species appeared to lack bothridial hooks entirely. Nonetheless, the otherwise remarkable similarities between these species and the species of Pedibothrium bearing bipronged hooks were considered to be sufficient to justify the placement of these 2 species in this genus. All 5 species possess proglottid features typical of Pedibothrium, including a uterus that extends anteriorly only to the level of the cirrus sac and a cirrus sac that is bent anteriorly and is crossed by the vagina. All 5 species also exhibit uniloculated bothridia. Of particular note was the fact that all 5 species exhibit bladelike spinitrichs with elongated distal tips, a form of microthrix currently known only from species of Pedibothrium. As a consequence, these species were treated as possessing modified hooks or as having lost hooks. The diagnoses of Pedibothrium and Onchobothriidae were emended to include these species. Each of the 5 new species bears a strong resemblance to 1 or more species of Pedibothrium hosted by a species of rhincodontid shark other than N. ferrugineus. Much of Southwell's type and voucher material of Pedibothrium was located and used to verify the identity of Pedibothrium kerkhami and many of the hosts from which Southwell's material of Pedibothrium was collected. This material suggests that P. kerkhami parasitizes Stegostoma fasciatum and not N. ferrugineus.

A revision of Platybothrium Linton, 1890 (Tetraphyllidea: Onchobothriidae), with a phylogenetic analysis and comments on host-parasite associations

A revision of Platybothrium Linton, 1890 is presented, based on available type and voucher material, as well as extensive new collections from elasmobranchs belonging to the Carcharhinidae (requiem sharks) and Sphyrnidae (hammerhead sharks). All 10 nominal Platybothrium species are treated or redescribed herein. Four of these 10 nominal species, in addition to one former member of Dicranobothrium Euzet, 1953, are considered valid members of Platybothrium. Five new Platybothrium species are described: P. angelbahiense n. sp. ex Carcharhinus leucas, P. coshtaprum n. sp. ex C. plumbeus, P. jondoeorum n. sp. ex Negaprion acutidens and C. melanopterus, P. kirstenae n. sp. ex C. obscurus, and P. tantulum n. sp. ex Sphyrna lewini and S. zygaena. Sixty-three morphological characters were employed in cladistic analyses of nine Platybothrium species and five outgroup species. Coding and analysis strategies were varied to assess the effects of coding inapplicable characters as missing or as a separate character state, and of excluding characters for which data are missing in more than 10% of the taxa. The analysis in which inapplicable characters were coded as a separate character state and no characters were excluded produced the best-supported and most conservative estimate of the interrelationships of Platybothrium spp. Platybothrium appears to be a monophyletic assemblage, with the most basal species being P. spinulifera Southwell, 1912. The group of species possessing an accessory piece between the hooks forms a clade within the genus. Species lacking an accessory piece, which had previously been placed in Dicranobothrium Euzet, 1953, do not appear to be each other's closest relatives; thus, Dicranobothrium is considered a synonym of Platybothrium. An examination of host associations indicated that Platybothrium species are broadly distributed among, and entirely restricted to, carcharhinid and sphyrnid shark species. Most Platybothrium species exhibit oioxenous host-specificity, with all but two species each parasitising only a single host species. In several host species, multiple Platybothrium congeners parasitise the same host individual, a phenomenon not previously reported for Platybothrium.

Calliobothrium spp. (Eucestoda: Tetraphyllidea: Onchobothriidae) in Mustelus schmitti (Chondrichthyes: Carcharhiniformes) from Argentina and Uruguay

Three species of Calliobothrium inhabit the spiral intestine of Mustelus schmitti in Argentina and Uruguay. Calliobothrium verticillatum australis is redescribed and its taxonomic status modified to species as C. australis. Calliobothrium barbarae n. sp. can be distinguished from all other species of Calliobothrium, which are small bodied, nonlaciniate, and without accessory piece between the bases of axial hook, by worm length, number of segments, cocoon morphology, and hooks shape. Calliobothrium lunae n. sp. is different from other Calliobothrium spp., which are small bodied, nonlaciniate. and have an accessory piece, by the number of segments and testes, hook shape, cocoon morphology, and the presence of ciliumlike projections on the distal surface of muscular pads. Calliobothrium australis is clearly distinguished from other large-bodied, laciniate species of the genus by worm length, number of testes, ovary shape, cocoon morphology, hook shape, and in being hyperapolytic. The oioxenous specificity involving Calliobothrium spp. and Mustelus spp. described by previous authors is confirmed in this study.