An ancient alliance: Matching evolutionary patterns of cartilaginous fishes (Elasmobranchii) and chloromyxid parasites (Myxozoa)

Myxozoa is a group of endoparasitic cnidarians covering almost 2600 species but merely 53 species, mostly from the genus Chloromyxum, have been reported from sharks, rays, and skates (Elasmobranchii). Elasmobranchs play a key role in the study of evolutionary trajectories of myxozoans as they represent ancestral vertebrate hosts. Our study provides new data on Chloromyxum spp. from 57 elasmobranchs, covering 20 species from geographical regions and host groups not previously investigated, such as Lamniformes and Hexanchiformes, the most basal phylogenetic shark lineage. In total, 28% of elasmobranchs were infected with Chloromyxum spp., indicating high diversity. Of the seven distinguished species, six are formally described based on morphological, morphometric, and genetic (18S rDNA) data. Comprehensive co-phylogenetic analyses and ancestral state reconstruction revealed that parasite and host phylogenies are clearly correlated, resulting in a distinct phylogenetic separation of chloromyxids from selachid (shark) vs. batoid (ray and skate) hosts. Species infecting the most ancient elasmobranchs formed a sublineage, branching off in the middle of the Chloromyxum sensu stricto clade. Our findings indicate that chloromyxids likely invaded an ancestral elasmobranch prior the time of divergence of shark and batoid lineages. Our analyses did not show a clear phylogeographic pattern of Chloromyxum parasites, probably due to the cosmopolitan distribution and migratory behaviour of many elasmobranch hosts, but geographical sampling must be extended to confirm or refute this observation. This study provides a complex view on species diversity, phylogeny, evolution, host-parasite co-phylogeny, and the phylogeographic origin of Chloromyxum species from elasmobranchs. Our results highlight the importance of adding missing data from previously un- or undersampled geographical regions and host species which results in a more accurate estimate of myxozoan biodiversity and a better understanding of the evolution of this parasite group in their hosts and in the different oceans of our planet.

Sea lice (Copepoda: Caligidae) from South Africa, with descriptions of two new species of Caligus

Thirteen species of sea lice (family Caligidae) are reported from a range of elasmobranch and actinopterygian fishes caught off South Africa or obtained from public aquaria in South Africa. Two new species of Caligus Müller, 1785 are described: C. linearis n. sp. from Pomatomus saltatrix (Linnaeus) and C. tumulus n. sp. from Chrysoblephus cristiceps (Valenciennes). A supplementary description is provided for both sexes of Caligus tetrodontis Barnard, 1948 taken from Amblyrhynchotes honckenii (Bloch) and previous records of this parasite from South African fishes are critically reviewed. It is concluded that Caligus material from Arothron hispidus Linnaeus was previously misidentified as C. tetrodontis and is in urgent need of re-examination. Morphological and molecular observations on Caligus furcisetifer Redkar, Rangnekar & Murti, 1949 indicate that this copepod is phenotypically and genetically identical to Lepeophtheirus natalensis Kensley & Grindley, 1973, and the latter becomes a junior subjective synonym of C. furcisetifer. We include new geographical distribution records for Caligus longipedis Bassett-Smith, 1898, C. rufimaculatus Wilson, 1905 and Lepeophtheirus spinifer Kirtisinghe, 1937, extending into South African waters, as well as both new distribution and host records for Alebion gracilis Wilson, 1905, Caligus dakari van Beneden, 1892 and Lepeophtheirus acutus Heegaard, 1943. The molecular analysis confirmed the monophyly of the genus Caligus. The South African species of Caligus did not cluster together, but the two included South African species of Lepeophtheirus were recovered as sister taxa.

The discovery of Lepeophtheirus acutus Heegaard, 1943 (Copepoda: Caligidae) from two new elasmobranch hosts in the Mediterranean Sea, and a comparative redescription of Lepeophtheirus rhinobati Luque, Chaves et Cezar, 1998

In this study, supplementary information on the morphology of the siphonostomatoid copepod Lepeophtheirus acutus Heller, 1865 is given based on new material collected from the ventral body surface and mouth cavity of common guitarfish, Rhinobatos rhinobatos (Linnaeus) and from the branchial cavity of bull ray, Aetomylaeus bovinus (Geoffroy Saint-Hilaire) caught in Iskenderun Bay, Turkey. This is the first report of L. acutus from Mediterranean waters. Key diagnostic characters of both sexes are reported, supported by light and scanning electron microscopy observations. In addition, Lepeophtheirus rhinobati Luque, Chaves et Cezar, 1998, which is closely related to L. acutus and has been reported from the same host genus, Rhinobatos, is reexamined based on paratypes stored in the collections of the United States National Museum of Natural History. Some of the key diagnostic characters which were incompletely known or lacking in the original description of both sexes of L. rhinobati are redescribed and/or presented for the first time.

Phylogenetic evidence for an ancestral coevolution between a major clade of coccidian parasites and elasmobranch hosts

Cartilaginous fishes are the oldest jawed vertebrates and are also reported to be the hosts of some of the most basal lineages of Cestoda and Aporocotylidae (Digenea) parasites. Recently a phylogenetic analysis of the coccidia (Apicomplexa) infecting marine vertebrates revealed that the lesser spotted dogfish harbours parasite lineages basal to Eimeria Schneider, 1875 and the group formed by Schellackia Reichenow, 1919, Lankesterella Ames, 1923, Caryospora Leger, 1904 and Isospora Schneider, 1881. In the present study we have found additional lineages of coccidian parasites infecting the cownose ray Rhinoptera bonasus Mitchill and the blue shark Prionace glauca Linnaeus. These lineages were also found as basal to species from the genera Lankesterella, Schellackia, Caryospora and Isospora infecting higher vertebrates. These results confirm previous phylogenetic assessments and suggest that these parasitic lineages first evolved in basal vertebrate hosts (i.e. Chondrichthyes), and that the more derived lineages infect higher vertebrates (e.g. birds and mammals) conforming to the evolution of their hosts. We hypothesise that elasmobranchs might host further ancestral parasite lineages harbouring unknown links of parasite evolution.

Redescription of Paraleptus chiloscyllii Yin et Zhang, 1983 (Nematoda: Physalopteridae) from the Arabian carpetshark Chiloscyllium arabicum (Chondrichthyes: Hemiscylliidae) off Iraq

The nematode Paraleptus chiloscyllii Yin et Zhang, 1983 (Physalopteridae) is redescribed on the basis of new material collected from the stomach of the Arabian carpetshark Chiloscyllium arabicum Gubanov (Hemiscylliidae) from marine waters off Iraq. Originally, P. chiloscyllii was found in C. plagiosum (Anonymous [Bennett]) from Fujian, China, but its description was rather poor and some important morphological features, such as deirids, shape and number of structures surrounding mouth, ventral unpaired papilla on the anterior cloacal lip, among others, were overlooked. It differs from its congeners in the shape of spicules and body length, although is very similar to the type species, P. scyllii Wu, 1927, only differing in the inequality of spicules. The generic diagnosis of Paraleptus was amended. Paraleptus minnanensis (Damin et Heqing, 2001) is considered a junior synonym of P. chiloscyllii and some morphological details of the posterior end of a male of P. australis Johnston et Mawson, 1943 are provided. The present finding of P. chiloscyllii in C. arabicum from off Iraq represents new host and geographical records.

Morphological and molecular characterisation of Ditrachybothridium macrocephalum Rees, 1959 (Cestoda: Diphyllidea) from Galeus melastomus Rafinesque in the Western Mediterranean

New morphological, molecular and ecological data for Ditrachybothridium macrocephalum Rees, 1959 (Cestoda: Diphyllidea) are presented and discussed based on specimens recovered from the blackmouth catshark Galeus melastomus Rafinesque (Scyliorhinidae) in the Western Mediterranean. A redescription of the plerocercus of this parasite is provided and new data on immature and mature worms including the first description of the eggs are reported, based on light and scanning electron microscopy observations. Analysis of 28S rDNA (domains D1-D3) sequences from plerocerci, immature and adult specimens revealed that they are conspecific with specimens from the North East Atlantic. Although previous authors considered that museum specimens identified as D. macrocephalum may represent more than one species, examination of type- and voucher material revealed no relevant morphological differences between museum specimens and the present material. Information on infection levels of D. macrocephalum is provided from a large number of host specimens (n = 170). This species was more abundant in juvenile than in adult hosts and on the middle slope than on the upper slope; this may be related to ontogenetic and bathymetric diet shifts of G. melastomus.

Diphyllidean cestodes from the bigeye houndshark Iago omanensis (Norman) (Carcharhiniformes: Triakidae) in the Gulf of Oman, with the description of Coronocestus ehsanentezarii sp. nov. (Echinobothriidae)

A new species of Coronocestus Caira, Marques, Jensen, Kuchta and Ivanov, 2013 is described from Iago omanensis (Norman) from the Gulf of Oman. Coronocestus ehsanentezarii sp. nov. differs from C. musteli (Pintner, 1889) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 in that its ovary is H- rather than U-shape. The new species is easily distinguished from C. diamanti (Ivanov and Lipshitz, 2006) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 by the number of spines per column on the cephalic peduncle (24-36 vs 95-118). It differs from C. hormozganiense (Haseli, Malek, Palm and Ivanov, 2012) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 based on a greater number of spines per column on the cephalic peduncle (24-36 vs 18-21). The new species differs from C. notoguidoi (Ivanov 1997) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 in that of its scolex is craspedote rather than acraspedote. Unlike C. coronatum (Robinson 1959) Caira, Marques, Jensen, Kuchta and Ivanov, 2013, C. ehsanentezarii sp. nov. possesses 29-35 rather than 20 apical hooks in each dorso-ventral group. The new species possesses lateral hooklets with two rows (a and b designations) in each cluster. This character had been presented earlier only for Andocadoncum Abbott and Caira, 2014. Furthermore, a new locality record is presented for C. diamanti from Iago omanensis in the Gulf of Oman. Thus, I. omanensis certainly hosts two diphyllidean species simultaneously in the Gulf of Oman. The generic diagnosis of Coronocestus is also revised to include new data.

Diversity of trypanorhynch metacestodes in teleost fishes from coral reefs off eastern Australia and New Caledonia

Trypanorhynch metacestodes were examined from teleosts from coral reefs in eastern Australia and from New Caledonia. From over 12,000 fishes examined, 33 named species of trypanorhynchs were recovered as well as three species of tentacularioids which are described but not named. Host-parasite and parasite-host lists are provided, including more than 100 new host records. Lacistorhynchoid and tentacularioid taxa predominated with fewer otobothrioid and gymnorhynchoids. Five species, Callitetrarhynchus gracilis, Floriceps minacanthus, Pseudotobothrium dipsacum, Pseudolacistorhynchus heroniensis and Ps. shipleyi, were particularly common and exhibited low host specificity. Limited data suggested a higher diversity of larval trypanorhynchs in larger piscivorous fish families. Several fish families surveyed extensively (Blenniidae, Chaetodontidae, Gobiidae, Kyphosidae and Scaridae) yielded no trypanorhynch larvae. The overall similarity between the fauna of the Great Barrier Reef and New Caledonia was 45%. Where available, information on the adult stages in elasmobranchs has been included.

Cavearhynchus, a new genus of tapeworm (Cestoda: Trypanorhyncha: Pterobothriidae) from Himantura lobistoma Manjaji-Matsumoto & Last, 2006 (Rajiformes) off Borneo, including redescriptions and new records of species of Pterobothrium Diesing, 1850

A new genus of trypanorhynch cestode is described from the tubemouth whipray Himantura lobistoma Manjaji-Matsumoto & Last, 2006 in the South China Sea off Malaysian Borneo. Cavearhynchus foveatus n. g., n. sp. possesses four pedicellate bothria in a cruciform arrangement, a heteroacanthous, heteromorphous metabasal tentacular armature with five hooks per principle row and an alternating longitudinal file of intercalary hooks on the bothrial surface of each tentacle, but lacks prebulbar organs and gland-cells within the bulbs. It, thus, closely resembles taxa belonging to the lacistorhynchoid family Pterobothriidae Pintner, 1931. However, the new genus differs from other genera within this family in the possession of bothrial pits. Although a distinguishing characteristic of the superfamily Otobothrioidea Dollfus, 1942, representatives of this group exhibit two bothria and the bothrial pits are lined with spiniform microtriches, whereas the pit-like structures.of C. foveatus n. g., n. sp. entirely lack microtriches. Redescriptions of two species of Pterobothrium, namely P. lesteri Campbell & Beveridge, 1996 and P. platycephalum (Shipley & Hornell, 1906) Dollfus, 1930 are provided from material collected off Borneo and several localities off Australia. Moreover, new host and locality records are added for P. australiense Campbell & Beveridge, 1996 and P. pearsoni (Southwell, 1929) Beveridge & Campbell, 1989.

The sea louse Lepeophtheirus acutus (Caligidae, Siphonostomatoida, Copepoda) as a pathogen of aquarium-held elasmobranchs

Lepeophtheirus acutus Heegaard, 1943 (Caligidae, Siphonostomatoida, Copepoda), was collected from or observed on four of six elasmobranch species held at Burgers' Zoo (Arnhem, The Netherlands). Circumstantial evidence suggested that a zebra shark, Stegostoma fasciatum (Hermann), from the wild carried the infection into the facility, where copepods reproduced and colonized additional hosts. Copepods typically attached on and about the eyes, in the mouth and occasionally about the cloaca and on the claspers. Severe ocular lesions were associated with infections on zebra sharks, a grey reef shark, Carcharhinus amblyrhynchos (Bleeker), whitetip reef sharks, Triaenodon obesus (Rüppell), and giant shovelnose ray, Rhinobatos typus Bennett, while blacktip reef sharks, Carcharhinus melanopterus (Quoy & Gaimard), and blacktip sharks, Carcharhinus limbatus (Valenciennes), living in infested aquaria showed no sign of infection. Water treatments using trichlorfon were considered primarily responsible for the eradication of copepods from hosts and infested aquaria. This case is the first report of a copepod infection being closely associated with disease and death of an aquarium-held elasmobranch. Given its ability to infect a wide variety of elasmobranchs and promote life-threatening lesions on some hosts, L. acutus should be considered a dangerous pathogen of captive elasmobranchs.

New host and geographical records of siphonostomatoid copepods associated with elasmobranchs off the KwaZulu-Natal coast, South Africa

The Siphonostomatoida (Copepoda) consists of 40 families comprised mainly of symbiotic members. Representatives of 12 families occur in symbiosis with elasmobranchs. Only eight families, 19 genera and 35 species have been reported from 37 elasmobranchs off the coast of South Africa. Elasmobranchs caught in the nets of the Natal Sharks Board and by fishermen of the Meer-en-See Boat Club, KwaZulu-Natal Province were examined for symbiotic siphonostomatoids. Additional to previous families reported, members of Cecropidae and Sphyriidae are being reported. Genera for the first time reported from South African waters include Entepherus, Carnifossorius, Eudactylina, Eudactylinodes, Kroeyerina, Pannosus, Phyllothyreus and Paeon. Therefore, currently ten siphonostomatoid families are reported from 49 species of elasmobranchs including 27 genera and 58 species.

Functional Richness, Functional Evenness, and Use of Niche Space in Parasite Communities

Most efforts aimed at elucidating the factors responsible for the variation in species richness among different parasite communities have focused on host characteristics such as body mass or diet. Independently of host features, however, the way in which parasites use resources within the host may also affect the species richness of the community. The distribution of parasite individuals or biomass in niche space determines whether host resources are used evenly, or whether there are gaps in resource use, with some parts of the total niche being underutilized. Here, the concepts of functional richness and functional evenness are applied to parasite communities for the first time, using simple indices. Measurements of the distribution of species in niche space within communities, such as mapping the distribution of helminths along the length of the host's intestine, is standard practice in parasitology. In such cases, functional richness is simply the proportion of the total number of intestine sections available that are used by at least 1 worm, whereas functional evenness measures the evenness in the distribution of worm numbers or biomass across all niche sections that are occupied. Data on cestode communities of elasmobranchs are used to illustrate the use of these indices, and to show how important they can be in tests of ecological hypotheses. The indices presented here capture essential features of resource use in parasite communities, and can be useful tools for comparative analyses.

Two new species ofPseudochristianellaCampbell & Beveridge, 1990 (Cestoda: Trypanorhyncha) from elasmobranch fishes from the Gulf of California, Mexico

Pseudochristionella elegantissima sp. nov. (Cestoda: Trypanorhyncha) is described from the spiral valves of the rays Dasyatis brevis (Garman, 1880) and D. longus (Garman, 1880), from the Gulf of California, Mexico. Also described is P. nudisculo sp. nov. from rays Rhinobatos productus Ayres, 1854, D. longus, Myliobatis longirostris Applegate & Fitch, 1964 and Zapteryx exasperat (Jordan & Gilbert, 1880) from the same location. The species are distinguished from one another and from the only existing species within the genus, P. southwelli Campbel & Beveridge, 1990, by differences in the arrangement of bill-hooks on the external surface of the basal swelling of the tentacle and by the number of hooks in each row of the metabasasl armature.

Taxonomic reports of Homeacanthoidea (Eucestoda: Trypanorhyncha) in Lamnid and Sphyrnid elasmobranchs collected off the coast of Santa Catarina, Brazil

Elasmobranch specimens of lamnid and sphyrnid captured in 1999 in the State of Santa Catarina, Brazil, were parasitized with homeacanthoid trypanorhynch cestodes: Isurus oxyrinchus Rafinesque, 1810 with Nybelinia lingualis (Cuvier, 1817) Dollfus, 1929; Sphyrna zygaena (Linnaeus, 1758) with Heteronybelinia rougetcampanae (Dollfus, 1960) Palm, 1999. New details of internal morphology and/or scolex and/or proglottid surface ultrastructure are given. Adults of N. lingualis are reported for the first time in the Brazilian coast.

Three new genera of trypanorhynch cestodes from Australian elasmobranch fishes

Three new genera of trypanorhynch cestodes from Australian elasmobranch fishes collected in the Arafura Sea, off the Northern Territory, are described. Fossobothrium perplexum n. g., n. sp. (Otobothriidae), from the spiral valves of Anoxypristis cuspidata (Latham) and Pristis zijsron Bleeker, is similar to the otobothriid genera Pseudotobothrium Dollfus, 1942 and Poecilancistrium Dollfus, 1929 in possessing bothrial pits and a band of hooks on the tentacle, but differs from all known otobothriid genera in having the pits joined by a prominent velum. Iobothrium elegans n. g., n. sp. (Otobothriidae), from the spiral valve of Himantura jenkinsi (Annandale), is placed in the Otobothriidae because it possesses bothrial pits, but differs from Otobothrium Linton, 1890 and other genera in lacking intercalary hooks between the principal rows and in possessing a chainette on the external surface of the tentacle in the metabasal region. Oncomegoides celatus n. g., n. sp. (Eutetrarhynchidae), from the spiral valve of Dasyatis microps (Annandale) and Himantura jenkinsi, resembles Oncomegas Dollfus, 1929 in possessing two bothria and a megahook on the bothrial surface of the basal armature, but differs in possessing an extra row consisting of four intercalary hooks formed by the overlapping of two intercalary hooks on the external tentacular surface between each of the opposing principal rows and is therefore an atypical heteroacanth.

Eutetrarhynchid cestodes from Atlantic and Mediterranean elasmobranch fishes, with the description of two new species of Dollfusiella Campbell & Beveridge, 1994 and redescriptions of Prochristianella papillifer (Poyarkoff, 1909) Dollfus, 1957 and Parachristianella trygonis Dollfus, 1946

Dollfusiella elongata n. sp. is described from the spiral valves of Rhinobatos rhinobatos (Linnaeus) and R. cemiculus Geoffroy St-Hilaire off the coast of Tunisia, while D. aculeata n. sp. is described from the spiral valves of Dasyatis pastinaca (Linnaeus) off the western coast of France, Dasyatis tortonesei Capape off the coast of Tunisia and Dasyatis chrysonota (Smith) var. marmorata off the coast of Senegal. A redescription of Dollfusiella spinifer (Dollfus, 1969) Campbell & Beveridge, 1994 is included based on the type-specimens from Myliobatis aquila (Linnaeus) from the Mediterranean coast of France. Prochristianella papillifer (Poyarkoff, 1909) Dollfus, 1957 is redescribed from specimens from Dasyatis pastinaca off Tunisia and the scolex and mature segments are described for the first time. Parachristianella trygonis Dollfus, 1946 is redescribed from Dasyatis pastinaca off the coast of France and Dasyatis tortonesei off Tunisia, with the mature and gravid segments being described for the first time. Parachristianella monomegacantha Kruse, 1959 is reported for the first time from the elasmobranchs Dasyatis pastinaca , Myliobatis aquila , Rhinobatos cemiculus and R. rhinobatos . Definitions of the related genera Dollfusiella Campbell & Beveridge, 1994 and Prochristianella Dollfus, 1946 are revised. Prochristianella spinulifera Beveridge & Jones, 2000 is transferred to Dollfusiella as D. spinulifera n. comb. New combinations proposed formally for the first time are: D. aetobati (Beveridge, 1990) n. comb., D. bareldsi (Beveridge, 1990) n. comb., D. lineata (Linton, 1909) n. comb., D. litocephalus (Heinz & Dailey, 1974) n. comb., D. macrotrachelus (Heinz & Dailey, 1974) n. comb., D. michiae (Southwell, 1929) n. comb., D. musteli (Carvajal, 1974) n. comb., D. schmidti (Heinz & Dailey, 1974) n. comb. and D. vooreemi (Sao Clemente & Gomes, 1989) n. comb. The type-specimens of Prochristianella tenuispinis (Linton, 1890) Dollfus, 1946 were re-examined and the species is transferred to Dollfusiella as D. tenuispinis (Linton, 1890) n. comb. Features of known species of Dollfusiella are presented in tabular form.

Taxonomic reports of Otobothrioidea (Eucestoda, Trypanorhyncha) from elasmobranch fishes of the southern coast off Brazil

Specimens of elasmobranch fishes, captured in the states of Paraná and Santa Catarina, of the southern coast off Brazil, represented by three families, four genera, and four species, were parasitized with otobothrioid trypanorhynch cestodes: Heptranchias perlo (Bonnaterre, 1788), Squalus sp. and Carcharhinus signatus (Poey, 1868) were parasitized with Progrillotia dollfusi Carvajal & Rego,1987; Prionace glauca (Linnaeus, 1758) with Molicola horridus (Goodsir, 1841) Dollfus, 1942. Details of internal morphology and/or scolex and/or proglottids surface ultrastructure, that expanded the description of M. horridus, through observations with lightfield, and/or scanning eletronic microscopy, are provided. The known geographical distribution for the species M. horridus is enlarged. P. dollfusi is reported for the first time in elasmobranchs.

Anthobothrium lesteri n. sp. (Cestoda: Tetraphyllidea) in Carcharhinus melanopterus from Heron Island, Australia, with comments on its site, mode of attachment, reproductive strategy and membership of the genus

Anthobothrium lesteri n. sp. in Carcharhinus melanopterus from Heron Island, Australia is described and figured. A combination of characters, namely the number of testes, a weakly laciniate strobila and mature proglottis which is conspicuously longer than wide distinguishes it from other species that appear to be consistent with van Beneden's original concept of Anthobothrium . The scolex and the peduncle are relatively small and frail when compared with the rest of the strobila and with the detached proglottis. A myzorhynchus is absent and the stalked, undivided, simple bothridia have thickened margins. Two circular areas of muscles, which resemble accessory suckers, occur in the centre of each bothridium. There is a distinct cephalic peduncle with spiniform blade-like microtriches followed by craspedote proglottides which have a posterior four-lobed velum. Apolysis is well developed and the oncosphere has a polar filament and a dense covering of spines. Comments are made on the site, the mode of attachment, an aspect of the reproductive strategy of the new species in relation to intestinal eversion in some sharks, and membership of the genus.

The plerocercus of Ditrachybothridium macrocephalum Rees, 1959 from two deep-sea elasmobranchs, with a molecular analysis of its position within the order Diphyllidea and a checklist of the hosts of larval diphyllideans

New collections were made of Ditrachybothridium macrocephalum Rees, 1959 from the deep-sea elasmobranchs Apristurus laurussonii (Saemundsson) and cf. Rajella bigelowi (Stehmann) in the northern Atlantic Ocean, allowing studies of the morphology of its plerocercus. The material has also allowed an estimate of its position within the Diphyllidea inferred from molecular data for the first time. The plerocercus is withdrawn, but not invaginated, within a cyst with a thick vacuolated wall. The encysted strobila is distinct, with several putative segments and advanced genital anlagen, and the scolex is fully developed with a distinct apical pad. 28S rDNA (D1-D3 regions) sequences were generated from both encysted and excysted D. macrocephalum , as well as from other diphyllidean and pseudophyllidean (outgroup) taxa for use in phylogenetic analyses. Maximum parsimony and Bayesian inference analyses both showed that the diphyllidean genus Echinobothrium is paraphyletic without inclusion of the only two other diphyllidean genera, Ditrachybothridium Rees, 1959 and Macrobothridium Khalil & Abdul-Salam, 1989. A list of published records of larval diphyllideans, their hosts and localities is included.

Anthobothrium altavelae sp. n. (Cestoda: Tetraphyllidea) from the spiny butterfly ray Gymnura altavela (Elasmobranchii: gymnuridae) in Tunisia

Seven Gymnura altavela (Linnaeus, 1758) (Elasmobranchii, Myliobatiformes) caught off the Tunisian coast were examined for endoparasites during a three-year period (1995-1998). A phyllobothriid cestode new to science was found in the spiral intestine of all host specimens. The presence of a tetrabothridiate scolex, bothridia lacking an apical sucker, laciniate strobila, and possession of postvaginal testes are sufficient to place this species in the genus Anthobothrium Van Beneden, 1850. In this genus, we consider that only two species, both previously reported from carcharhiniform sharks, are valid: Anthobothrium cornucopia Van Beneden, 1850 and A. laciniatum Linton, 1890. Anthobothrium altavelae sp. n. can be distinguished from its congeners by its length, strobila morphology, and the number of testes. The taxonomic position of the species attributed to Anthobothrium parasitic in gymnurids is discussed.

Light and scanning electron microscopy observations on Gnathia vorax (Isopoda: Gnathiidae) larvae

A large population of gnathid isopods (Crustacea) has been observed on sea water teleost fishes coming from the Civic Aquarium of Messina (Italy). Gnathiidae are parasite of fishes only at the stage of praniza, while adults are free living. Several teleosts, reared in captivity at the Civic Aquarium of Messina were sent for parasitological examination over a period of three years. Numerous parasites, identified as pranizae of Gnathiidae, were found on dorsum, on dorsal, pectoral and caudal fins, as well as in oro-pharyngeal cavity and gills of the affected fishes. The cranial part of an exuvie of adult male belonging to Gnathia sp. was also found on the floor of the tank. Because adult parasites are rarely detected in the sand bottom, the taxonomic identification is based on the morphological characteristics of larvae, even if it is very hard to show interspecific differences among gnathiids. For this reason, the morphological study was performed also by SEM to better show the surface details with taxonomic meaning. One to five mm long pranizae had a flattened body characterised by a head followed by 5 thoracic and 6 abdominal segments and a caudal plate with two biarticulated uropods. In the oral part of the head there was a ventrally oriented and smooth trapezoidal rostrum. Oral appendages, not clearly visible by light microscopy, were: a) two jaws with denticulate internal sides longer than the rostrum; b) a single ipostoma apically divided into two long appendixes; c) long and thin maxillae, with denticulate distal margins; d) two paired maxillipedes showing ciliate internal side that reaches the extremity of buccal cone; e) two big gnatopods with apical nail. Flagellum of antennulae had 7 articles. Telson was triangularly shaped, longer than large, with truncated apex having two apical bristles. Uropods were short with rounded internal angle and were provided by smooth and plumose setae; endopod was larger than exopod. The jaw of the adult gnathiid male, studied only by light microscopy, was solid, with oblique and denticulated blade; long and thin apex; rounded internal lobe; prominent external spur. Morphological characteristics of the jaw of the adult male and the shape of larvae permitted us to identify our specimens as Gnathia vorax (Lucas, 1850).

Gnathia pantherina sp. n. (Crustacea: Isopoda: Gnathiidae), a temporary ectoparasite of some elasmobranch species from southern Africa

Haematophagous larvae of a gnathiid isopod were collected from the gills, nares and buccal cavity of a single leopard catshark Poroderma pantherinum (Smith, 1838) at Jeffreys Bay and five puffadder shysharks Haploblepharus edwardsii (Voight, 1832) and one blackspotted electric ray Torpedo fuscomaculata Peters, 1855, at the De Hoop Nature Reserve on the South African south coast. Larvae were kept in fresh seawater until their moult into adult stages. The morphology of the adult males did not conform to that of any known species and they are therefore described as Gnathia pantherina sp. n. The descriptions of the adult male, female and praniza larva are based on light and scanning electron microscopy observations. Characteristic features of this species include the large size of all the final life-cycle stages, the deeply divided mediofrontal process of the male, the morphology of the pylopods and maxillipedes of the female, and the number of teeth on the mandibles (eight) and maxillules (seven) of the praniza larvae.

Trimusculotrema schwartzi n. sp. (Monogenea: Capsalidae) from the skin of the stingray Dasyatis zugei (Elasmobranchii: Dasyatidae) off Hong Kong, China

Trimusculotrema schwartzi n. sp. (Capsalidae) is described from the skin of the stingray Dasyatis zugei (Elasmobranchii: Rajiformes: Dasyatidae) off Hong Kong, China. Only three other species have been placed in the genus Trimusculotrema: T. micracantha (Euzet & Maillard, 1967), T. leucanthemum (Euzet & Maillard, 1967), and T. uarnaki Whittington & Barton, 1990. T. schwartzi n. sp. may be differentiated from all known species of Trimusculotrema by the length of the anterior hamuli and by the absence of pigment shields over the eye-spots. Its occurrence on a stingray off China represents a northern extension of the geographical range of Trimusculotrema.

Digenea and acanthocephala of elasmobranch fishes from the southern coast of Brazil

New records for helminth species recovered from elasmobranch fishes in Brazil are established. Digenean and acanthocephalan parasites of elasmobranch fishes are reported from the southern coast of Brazil: Otodistomum veliporum (Creplin, 1837) Stafford, 1904 (Digenea: Azygiidae) in the stomach and spiral valve of Dipturus trachydermus and in the spiral valve of Squatina sp. Cystacanths and juveniles of the acanthocephalans Corynosoma australe Johnston, 1937 and Corynosoma sp., in the spiral valve of Squatina sp., Galeorhinus galeus and Hexanchus griseus and in the stomach of Squalus megalops; a juvenile of Gorgorhynchus sp., in the spiral valve of Sphyrna zygaena. Dipturus trachydermus and Squatina sp. are new host records for O. veliporum. Digeneans and acanthocephalans are reported for the first time parasitizing elasmobranch fishes in Brazil.

Erudituncus n. gen. (Tetraphyllidea: Onchobothriidae) with a redescription of E. musteli (Yamaguti, 1952) n. comb. and comments on its hook homologies

Examination of type and new material of Platybothrium musteli Yamaguti, 1952, resulted in the erection of a new genus, Erudituncus, the new combination Erudituncus musteli (Yamaguti, 1952), and the redescription of the newly combined species. This species exhibits novel hook morphology. Each bothridium bears 2 pairs of hooks, the axial pair comprising 1 medial and 1 lateral bipronged hook and the abaxial pair comprising a lateral unipronged hook and a medial, simple hook element. Based on the position of the hook talons, we suggest that the inner prong of the axial hooks of Erudituncus is homologous to the single prong of the axial hooks of Calliobothrium and the axial prongs of Dicranobothrium, Platybothrium, Phoreiobothrium, and Onchobothrium; the outer prong of the axial hooks of Erudituncus is homologous to the abaxial prongs of Dicranobothrium, Platybothrium, Phoreiobothrium, and Onchobothrium; and the abaxial hooks of Erudituncus and Calliobothrium are homologous. Erudituncus musteli was lacking from 31 individuals of the type host of record, the triakid shark Mustelus manazo Bleeker, 1854, examined for this study, but was obtained from 2 individuals of the triakid shark Hemitriakis japanica (Muller and Henle, 1839). Therefore, H. japanica is proposed as the probable type host of E. musteli.

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

There is general consensus that the living elasmobranchs comprise a monophyletic taxon. There is evidence that, among tetraphyllidean tapeworms, the approximately 201 hooked species (Onchobothriidae) may also comprise a monophyletic group. Determinations of host specificity are contingent upon correct specific identifications. Since 1960, over 200 new elasmobranch species and over 100 new onchobothriid species have been described. Some confidence can be placed in host and parasite identifications of recent studies, but specific identifications provided in older literature in many cases are suspect. There is some consensus among published works on the phylogenetic relationships among elasmobranchs. Phylogenetic relationships among onchobothriids remain largely unresolved. Elasmobranchs have been poorly sampled for onchobothriids; records exist for approximately 20% of the 911 species and approximately 44% of the 170 elasmobranch genera. Onchobothriids are remarkably host specific, exhibiting essentially oioxenous specificity for their definitive hosts. Multiple onchobothriid species commonly parasitise the same host species; in some cases these are congeners, in other cases these are members of two different onchobothriid genera. There is substantial incongruence between available host and parasite phylogenies. For example, Acanthobothrium is by far the most ubiquitous onchobothriid genus, parasitising almost all orders of elasmobranchs known to host onchobothriids, yet, there is no evidence of major clades of Acanthobothrium corresponding to postulated major subgroupings of elasmobranchs (e.g. Galea and Squalea or sharks and rays). Potamotrygonocestus appears to be among the most basal onchobothriid groups, yet it parasitises one of the most derived elasmobranch groups (the freshwater stingray genus Potamotrygon). It appears that congeners parasitising the same host species are not necessarily each other's closest relatives. At this point the preliminary and limited available data suggest that, at least in this system, strict host specificity is not necessarily indicative of strict co-evolution. This study was extremely limited by the lack of available robust phylogenies for onchobothriids and elasmobranchs.

Tetraphyllidean metacestodes of teleosts of the Great Barrier Reef, and the use of in vitro cultivation to identify them

The tetraphyllidean metacestode diversity of 310 teleost fishes, including 87 species from 31 families, was examined from Heron Island, The Great Barrier Reef, Australia. Eleven metacestode 'types' were identified with the use of light microscopy. Host-specificity varied greatly among metacestode types. Incorporation of in vitro cultivation allowed generic identification for some types. Types 1 and 2 belong to Uncibilocularis Southwell, 1925, and have triloculate bothridia and one pair of forked hooks with unequal prongs; Type 3 has quadriloculate bothridia. Hook development was insufficient to determine in which genus, Acanthobothrium van Beneden, 1849 or Calliobothrium van Beneden, 1850, this type may belong. Type 4 has unilocular bothridia with simple edges and belongs to Anthobothrium van Beneden, 1850. Type 5 has multiloculated bothridia which are invaginated within pouches. This type belongs to the Rhinebothriinae although its generic identity cannot be determined. The bothridia of Type 5 everted within 24 hours of in vitro cultivation and revealed the presence of two forms, one having 48 loculi per bothridium, the other 72 per bothridium. In vitro studies provide additional support for existing theories of onchobothriid scolex development.

Four new species of Acanthobothrium (Cestoda: Tetraphyllidea) from the whiptail stingray Dasyatis brevis in the Gulf of California, Mexico

Examination of the spiral intestines of 29 whiptail stingrays, Dasyatis brevis, from 6 sites in the Gulf of California, Mexico in 1993 and 1996 resulted in the discovery of 4 new species of Acanthobothrium: Acanthobothrium bullardi, Acanthobothrium dasi, Acanthobothrium rajivi, and Acanthobothrium soberoni. This brings the total number of species of Acanthobothrium known from the eastern Pacific Ocean to 34. With 22 additional species reported from elasmobranchs from the western Atlantic Ocean, and over 100 species globally, the number of interspecific comparisons required to justify the designation of a new species is rather unwieldy. To facilitate these and future comparisons, and in the absence of a phylogenetic hypothesis for this genus, the 56 species of Acanthobothrium from these 2 geographic regions were categorized for 4 characters: total length (< or = or > 15 mm), number of segments (< or = or > 50 segments), number of testes (< or = or > 80), and symmetry of poral and aporal ovarian lobes. These 56 taxa and their categories are presented in tabular form. Based on these characters, A. bullardi, A. dasi, and A. rajivi are category 2 species (they are relatively small, possess few segments, relatively few testes, and exhibit asymmetrical ovaries); A. soberoni is a category 6 species (it is a relatively longer worm with a larger number of segments, but with fewer testes and an asymmetrical ovary). All 4 species differ from 1 another and from species in other geographic regions in further subtleties of these 4 characters as well as hook size and relative length of hook prongs, cirrus sac size, genital pore position, number of columns of testes anterior to the cirrus sac, and number of postvaginal testes. Five specimens that appear to represent a new species of Acanthobothroides were also collected. This species is figured and some details of the morphology are described, but the material was considered to be insufficient to allow for formal description of this species at this time. This is the first record of either of these genera of onchobothriid tapeworms from the Gulf of California.

Diphyllidean cestodes of the Gulf of California, México with descriptions of two new species of Echinobothrium (Cestoda: Diphyllidea)

As part of a survey of parasites of elasmobranchs in the Gulf of California, a second and final report of the diphyllidean cestodes resulting from the survey is presented. Of 43 species of elasmobranchs examined for parasites, 7 (Rhinobatos productus, Rhinobatos leucorhynchus, Myliobatis californicus, Myliobatis longirostris, Urobatis halleri, Urobatis maculatus, and Rhinoptera steindachneri) were found to host diphyllidean cestodes, all belonging to Echinobothrium. No species of either of the other 2 diphyllidean genera, Dirrachybothridium or Macrobothridium, were discovered. A greater diversity of diphyllideans was found in 1996 than in 1993. Two new species, Echinobothrium hoffmanorum n. sp. and Echinobothrium rayallemangi n. sp. are described from the spiral intestines of U. maculatus and R. leucorhynchus, respectively. Echinobothrium hoffmanorum is unique in its possession of the following combination of characters: 19-21 apical hooks in each dorsoventral group, 12-22 lateral hooklets in each group, 10-17 cephalic peduncle spines per column, 4-8 testes, 4-10 segments and eggs with a single filament. Echinobothrium rayallemangi is unique in its possession of the following combination of characters: 23 apical hooks in each dorsoventral group, 20-23 lateral hooklets in each group, 2-5 cephalic peduncle spines per column, 4-6 testes, and 4-6 segments. These 2 new species, together with Echinobothrium mexicanum and Echinobothrium fautleyae, brings the total number of diphyllideans known from the Gulf of California to 4. The survey of diphyllidean cestodes of the Gulf of California has resulted in a new host record for Echinobothrium for each of the host species mentioned above, with Rhinobatos and Urobatis representing new host genera and Urolophidae a new host family for Echinobothrium.

Calicotyle californiensis n. sp. and Calicotyle urobati n. sp. (Monogenea: Calicotylinae) from elasmobranchs in the Gulf of California

Two new species of Calicotyle (Monocotylidae: Calicotylinae) are described from elasmobranchs in the western Gulf of California. Calicotyle californiensis n. sp. is described from a single specimen collected from a gray smoothhound shark (Mustelus californicus, Carcharhiniformes: Triakidae). It is distinguished from its congeners by the combination of having vaginal pores opening within the intercecal space, distal regions of the vaginae twisting, proximal regions of the vaginae fusing medially to form a kidney bean-shaped structure, and a relatively long male copulatory organ recurving 3 times and passing between the distal penis bulb and the seminal vesicle. Calicotyle urobati n. sp. is described from 16 specimens collected from at least the cloaca and rectum of the round rays Urobatis halleri and Urobatis maculatus (Rajiformes: Urolophidae). It is distinguished from its congeners by the combination of having vaginal pores opening outside the intercecal space and proximal regions of the vaginae terminating at the level of the ceca. Members of Calicotyle have not been reported previously from the eastern Pacific Ocean or from these hosts. In the past, species of Calicotyle have been distinguished based primarily on the shape and length of the male copulatory organ and hamuli. Divisions of the vaginae and the positions of the vaginal pores are also useful in distinguishing members of the genus.

Rhopalobdella japonica n. gen., n. sp. (Hirudinea, Piscicolidae) from Dasyatis akajei (Chondrichthyes: Dasyatididae) in the northwestern Pacific

A new genus and species of piscicolid leech in the Platybdellinae inhabits the oral cavity of Dasyatis akajei in the northwestern Pacific Ocean near Tanabe, Japan. The genus Rhopalobdella n. gen. is characterized externally by very small oral and caudal suckers and a smooth body that is widest just posterior to the clitellum. Eyespots and ocelli are lacking. The coelom is spacious with large segmental connecting sinuses between dorsal and ventral sinuses. There are 5 pairs of testisacs, an unusually extensive epididymis, and a very large bursa. Conducting tissue is absent. There are 2 pairs of esophageal diverticula and very well developed nephridia. Rhopalobdella japonica n. gen. n. sp. is characterized by a urosome that tapers strongly to the caudal sucker and by a single gonopore; the common oviduct opens into the posterior portion of the bursa. The coelomic and excretory systems resemble Aestabdella, but in other respects the genera are quite different. This is the first marine leech reported from rays in the northwestern Pacific.

A new species of Neoheterocotyle Hargis, 1955 (Monogenea: Monocotylidae) from the gills of Pristis clavata Garman (Pristidae) from Darwin, Australia

Neoheterocotyle darwinensis n. sp. is described from between the secondary gill lamellae of the dwarf sawfish Pristis clavata Garman (Pristidae) collected at the mouth of Buffalo Creek near Darwin, Northern Territory, Australia. This is only the second monocotylid species to be described from northern Australia. N. darwinensis is distinguished from the other seven valid species in the genus by the morphology of the hamuli, the dorsal haptoral accessory sclerites and the male copulatory organ. The similarities between N. darwinensis and Nonacotyle pristis Ogawa, 1991 from the gills of the freshwater sawfish Pristis microdon Latham collected in Papua New Guinea are discussed.

New species of Spinuris (monogenea: monocotyladae) from Zapteryx exasperata (elasmobranchii: rhinobatidae) from Baja California Sur, Mexico

Monocotylid monogeneans were collected from the gills of 2 Rhinobatos productus and 5 Zapteryx exasperata in Bahia Almeja, Baja California Sur, Mexico. All are parasitized by monocotylids of the genus Spinuris, 9 specimens of Spinuris lophosoma Doran on Rhinobatos productus (new record) and 27 specimens of Spinuris zapterygis n. sp. on Z. exasperata. This new species differs from the other species in the genus Spinuris by the number of dorsal haptoral sclerites, morphology of hooks, and male copulatory apparatus. The generic diagnosis of the genus Spinuris is revised.

Studies on the new species Tylocephalum chiralensis, parasite from Dasyatis (Himantura) uarnak (Förskal) from Chirala coast, Andhra Pradesh, India

A new species of the cestode genus Tylocephalum obtained from the host Dasyatis uarnak is described. A detailed examination of specimens have allowed us to erect a new species Tylocephalum to accommodate the worm. It shows remarkable differences from other known species of Tylocephalum in large size of the worm, absence of neck, variation in number of testes arrangement of vitellaria and genital openings. The new species is designated as Tylocephalum chiralensis.