Tapeworms (Platyhelminthes, Cestoda) from marine chondrichthyans of the Southwestern Atlantic Ocean, and the sub-Antarctic and Antarctic islands: a checklist

A parasite-host list of cestodes parasitizing chondrichthyans in the Southwest Atlantic off Argentina and surrounding waters of Antarctica is compiled based on the available literature. The list is based on published descriptions and redescriptions of species, and newly collected worms during the current study. A total of 57 valid species belonging to 28 genera of the orders Cathetocephalidea, Diphyllidea, Gyrocotylidea, Lecanicephalidea, Onchoproteocephalidea, Phyllobothriidea, Rhinebothriidea, "Tetraphyllidea", and Trypanorhyncha is listed. Information on hosts, localities, specimens in collections and comments on tapeworms are also included. A host-parasite list including chimaeras (1 order, 1 genus), batoids (4 orders, 10 genera), and sharks (3 orders, 5 genera) is provided. Tapeworm diversity, distribution range, and host associations are discussed. The cestodes orders Phyllobothriidea and Rhinebothriidea exhibit the highest species richness, with 13 and 12 species, respectively. Onchoproteocephalideans and rhinebothriideans have the broadest geographic distribution in the study area. Regarding hosts, arhynchobatid skates are the group most frequently associated with cestodes. However, further collecting efforts are necessary to understand whether this data reflect the real diversity and host association of these parasites or is a result of a bias in sampling.

New species of Guidus Ivanov, 2006 (Cestoda: Phyllobothriidea) from Bathyraja magellanica (Philippi) from the Patagonian Continental Shelf of Argentina

Specimens representing two new species of Guidus Ivanov, 2006 were collected from the Magellan skate (Bathyraja magellanica [Philippi]) in the Patagonian Continental Shelf of Argentina, Southwestern Atlantic Ocean. Guidus francoi sp. n. and Guidus magellanicus sp. n. differ from their congeners by a particular combination of features, including type of bothridia, worm length, number of testes, and distribution of vitelline follicles. Guidus francoi sp. n. is distinguished from G. magellanicus sp. n. by having fewer proglottids, fewer testes and a higher ratio between the cirrus sac length and the proglottid width. The microthrix pattern of species of Guidus from the Southwestern Atlantic is described, based on specimens of G. francoi sp. n., Guidus magellanicus sp. n., and newly collected specimens of Guidus argentinense Ivanov, 2006. These three species share the presence of wide aristate gladiate spinitriches on the proximal bothridial surface, narrow gladiate spinitriches on the bothridial rim, and filitriches on the distal bothridial surface. The diagnosis of Guidus is revised to include several features exhibited by the new species (i.e., presence of bothridial indentations and bothridial stalks, distribution of vitelline follicles, and eggs grouped in cocoons). The discovery of G. francoi sp. n. and G. magellanicus sp. n. from B. magellanica increases the number of species of Guidus collected from batoids in the Southwestern Atlantic from one to three. The specificity exhibited by the species herein described reinforces the tight association between rays in the genera Guidus and Bathyraja.

Emerging global novelty in phyllobothriidean tapeworms (Cestoda: Phyllobothriidea) from sharks and skates (Elasmobranchii)

New genera are erected for three clades of tapeworms originally discovered using molecular sequence data. The morphological features of each are characterized after examination of specimens with light and scanning electron microscopy. Rockacestus gen. nov. parasitizes skates. Ruhnkebothrium gen. nov. parasitizes hammerhead sharks. Yamaguticestus gen. nov. parasitizes small squaliform sharks and catsharks. The novelty of these genera is supported by a taxonomically comprehensive molecular phylogenetic analysis of the D1–D3 region of the 28S rDNA gene, which, with the addition of newly generated sequence data, is the first to include representation of 15 of the 18 genera of phyllobothriideans plus the three new genera. Five new species are described from elasmobranchs in the western Atlantic Ocean, the Gulf of California, Chile, the Falkland Islands and South Africa to help circumscribe the new genera. Two of the genera provide appropriate generic homes for ten species of phyllobothriideans from catsharks and skates with uncertain generic affinities and thus resolve longstanding taxonomic issues. Given that these genera parasitize some of the most poorly sampled groups of elasmobranchs (i.e. hammerhead sharks, squaliform sharks, catsharks and skates), based on the strict degree of host specificity observed, we predict that further work on other members of these groups will yield as many as 200 additional species in these three genera of tapeworms globally. This brings the total number of genera in the Phyllobothriidea to 21.

Morphological variation in the hyperapolytic lecanicephalidean species Anteropora japonica (Yamaguti, 1934) (Eucestoda)

In November of 2013, a specimen of Japanese sleeper ray, Narke japonica (Temminck et Schlegel), caught off Nanfang-ao, Taiwan was found to be parasitised by the cestode Anteropora japonica (Yamaguti, 1934). Specimens comprised whole worms and free proglottids, both of varying degrees of maturity. This material allowed for the opportunity to examine in detail the developmental progression of this hyperapolytic lecanicephalidean species with regard to overall size, scolex dimensions, and microthrix pattern. Complete immature worms ranged in size from 2.4 mm to 14 mm. The smallest scoleces were half as wide as larger scoleces and exhibited a much smaller ratio of apical organ width to bothridial width. Proglottids more than quadrupled in length during maturation from terminal attached immature to detached proglottids. In addition, a change in microthrix pattern was observed on the anterior region of the proglottids from immature to gravid proglottids; the anterior region of attached immature proglottids is covered with gladiate to coniform spinitriches with capilliform filitriches only rarely visible, whereas this region in detached proglottids is covered with gladiate to coniform spinitriches and conspicuous capilliform filitriches. This is the first report of A. japonica from outside Japan expanding its distribution south to Taiwan. In addition, a preliminary phylogenetic analysis of the genus is presented that suggests congeners from the same host species are not each other's closest relatives, nor is there an apparent phylogenetic signal for apical organ type or reproductive strategy (apolysis). However, reproductive strategy does seem to be correlated with host group such that euapolytic species parasitise dasyatid stingrays while hyperapolytic species parasitise either torpediniform rays or orectolobiform sharks.

Site specificity and attachment mode of Symcallio and Calliobothrium species (Cestoda: "Tetraphyllidea") in smoothhound sharks of the genus Mustelus (Carcharhiniformes: Triakidae)

Previous studies suggest that cestodes (i.e., tapeworms) of the sister genera Symcallio and Calliobothrium attach in different specific regions of the spiral intestine of their triakid shark hosts, with species of Symcallio attaching in the anterior region of the spiral intestine and species of Calliobothrium attaching with a broader distribution centered around the middle of the spiral intestine. In the present study, we tested the generality of this pattern of site specificity in two additional species pairs: Symcallio peteri and Calliobothrium euzeti in Mustelus palumbes and S. leuckarti and C. wightmanorum in M. asterias. Finding that these cestodes also exhibit the aforementioned pattern, we investigated a series of functional explanations that might account for this phylogenetically conserved pattern of site specificity. The mucosal surface of the spiral intestine of both shark species was characterized, as were the attachment mechanisms of all four cestode species. Although anatomical differences in mucosal surface were seen along the length of the spiral intestine in both shark species, these differences do not appear to correspond to the attachment mode of these cestodes. We find that while species of Symcallio, like most cestodes, attach using their scolex, species of Calliobothrium attach with their scolex and, to a much greater extent, also with their strobila. Furthermore, attachment of Calliobothrium species appears to be enhanced by laciniations (flap-like extensions on the posterior margins of the proglottids) that interdigitate with elements of the mucosal surface of the spiral intestine. The role of proglottid laciniations in attachment in species of Calliobothrium helps reconcile a number of morphological features that differ between these two closely related cestode genera.

A New Genus of Tapeworm (Cestoda: Onchoproteocephalidea) from Sawfish (Elasmobranchii: Pristidae)

Collections from the dwarf sawfish, Pristis clavata, near Darwin, Australia, in 1997 led to the discovery of the new onchoproteocephalidean genus Matticestus n. gen.-a taxon that has been referred to in molecular phylogenetic analyses in which it has been included as "New genus 8." Its type species, Matticestus anneae n. gen., n. sp., and a second species, Matticestus kathleenae n. sp., are described. Placement of this taxon in the Onchoproteocephalidea is supported morphologically in that both species bear a scolex with 4 bothridia each with a pair of bi-pronged hooks and spinitriches that extend throughout the length of the body. Sequence data for the D1-D3 region of the 28S rDNA gene also place the genus solidly among the other elasmobranch-hosted members of the order. The new genus differs from the other elasmobranch-hosted genera in the order in that its members possess a combination of biloculated bothridia with lateral lappets on the posterior margin of the anterior loculus and a pair of bi-pronged hooks with a distinctive configuration of tubercles and internal channels. Its members are also extremely small. In summary, Matticestus n. gen. is an unusually tiny, "spiny," genus of cestode that seems to exclusively parasitize sawfish of the genus Pristis.

Squalus bassi sp. nov., a new long-snouted spurdog (Chondrichthyes: Squaliformes: Squalidae) from the Agulhas Bank

The long-snouted African spurdog Squalus bassi sp. nov. is described based on material collected from the outer shelf and upper continental slope off South Africa and Mozambique. Squalus bassi shares with S. mitsukurii, S. montalbani, S. chloroculus, S. grahami, S. griffini, S. edmundsi, S. quasimodo and S. lobularis a large snout with prenarial length greater than distance between nostrils and upper labial furrows, dermal denticles tricuspidate and rhomboid and elevated number of vertebrae. Squalus bassi can be distinguished from all its congeners by a combination of body and fin colouration, external morphometrics, vertebral counts and shape of dermal denticles. Similar long-snouted congeners from the Indo-Pacific region, including S. montalbani, S. edmundsi and S. lalannei are compared in detail with the new species. This new species has been misidentified as the Japanese S. mitsukurii and the Mediterranean S. blainvillei due to the lack of comparative morphological analyses. The validity of the nominal species S. mitsukurii in the south-eastern Atlantic Ocean and western Indian Ocean is also clarified herein, indicating it has a more restricted geographical distribution in the North Pacific Ocean.

Diversity, phylogenetic relationships and host associations of Calliobothrium and Symcallio (Cestoda: ‘Tetraphyllidea') parasitising triakid sharks

The laciniate, relatively large-bodied tetraphyllidean tapeworm genus Calliobothrium van Beneden, 1850 parasitises triakid sharks with all but one species found parasitising sharks of the genus Mustelus Linck, 1790. Historically, species of this genus were thought to exhibit a relaxed degree of host specificity relative to species of their sister genus Symcallio Bernot, Caira, & Pickering, 2015. However, several more recent studies have begun to question this difference and, in particular, the conspecificity of specimens identified as the types species, C. verticillatum (Rudolphi, 1819) van Beneden, 1850, from multiple host species. Our results suggest that diversity in the genus Calliobothrium has been under-reported. To explore this situation, specimens previously identified as C. verticillatum were collected from Mustelus asterias Cloquet, 1819 off the United Kingdom and Mustelus canis (Mitchell, 1815) off Connecticut, USA; these sharks each were found to host distinct species both of which are described here. Mustelus asterias was also confirmed to host Symcallio leuckarti (van Beneden, 1850) Bernot, Caira & Pickering, 2015, which is redescribed. In combination with newly collected material from Mustelus palumbes Smith, 1957 off South Africa and data available from GenBank, molecular phylogenetic analyses based on 28S rDNA data for four of the seven known species of Calliobothrium, including both new species and five of the 11 known species of Symcallio, were conducted. The resulting phylogeny supports the mutual monophyly of the two genera, which are readily distinguished based on whether they exhibit proglottid laciniations, and supports subclades of Symcallio with and without hook accessory pieces. These subclades of Symcallio appear to exhibit an intriguing congruence with two known subclades of their host genus, Mustelus.

The dismantling of Calliobothrium (Cestoda: Tetraphyllidea) with erection of Symcallio n. gen. and description of two new species

This paper aims to resolve the dual composition of the triakid shark-hosted tetraphyllidean genus Calliobothrium--an issue that has been recognized for over a decade. As it stands, this genus includes a number of large species with laciniate proglottids, most of which bear 3 suckers at the anterior margin of each bothridium, but it also includes a number of species that lack proglottid laciniations and bear only a single sucker per bothridium, most of which are relatively small. Discovery of 2 new species, 1 of each form, parasitizing the whitespot smoothhound shark, Mustelus palumbes, off South Africa, prompted the first molecular analysis of the genus. Bayesian inference and maximum likelihood analyses of 28S rDNA (D1-D3) sequence data generated for specimens of both new species as well as of 2 known species of the laciniate form (Calliobothrium australis and Calliobothrium cf. verticillatum) and 3 known species of the non-laciniate form (Calliobothrium violae, Calliobothrium riseri, and Calliobothrium barbarae) confirmed the reciprocal monophyly of the 2 clades, supporting establishment of a new genus. Because the type of Calliobothrium, C. verticillatum, is of the laciniate form, Symcallio n. gen., with Symcallio peteri n. gen., n. sp., from M. palumbes described as its type, is established to house members of the non-laciniate clade. The 11 described species consistent with this form are transferred to the new genus. A new species of the laciniate clade, Calliobothrium euzeti n. sp., is described from M. palumbes, and a revised diagnosis of Calliobothrium is presented.

An enigmatic new tapeworm, Litobothrium aenigmaticum, sp. nov. (Platyhelminthes : Cestoda : Litobothriidea), from the pelagic thresher shark with comments on development of known Litobothrium species

An enigmatic new tapeworm is described from pelagic thresher sharks in México and Taiwan. While lsrRNA (D1-D3) data robustly place it in the Litobothriidea, it bears essentially no morphological resemblance to other members of the order. Instead it superficially resembles the freshwater fish-inhabiting Caryophyllidea. Its scolex consists of a simple dome-shaped scolex proper and an extensive cephalic peduncle housing four distinct tissue types. It is hyperapolytic, thus reproductive anatomy is unknown. Developmental data show typical litobothriideans bear basic elements of their adult scolex upon entering the definitive host, undermining the notion that the new cestode represents a distinct litobothriidean life cycle stage. Scanning electron microscopy revealed the new species shares bands of distinctive microtriches with its congeners. In combination these data justify establishment of Litobothrium aenigmaticum, sp. nov.; the generic, familial and ordinal diagnoses are emended accordingly. Unlike typical litobothriideans, each worm is associated with a mucosal expansion at its attachment site, like those seen in some caryophyllideans. This pathological change may represent a worm-induced host response serving to reinforce attachment of the simple scolex to the mucosa. If so, the convergence of this litobothriidean on a morphology like that seen in the distantly related Caryophyllidea is a result of similarity in mode of attachment.