New species of Rhinebothrium Linton, 1890 (Cestoda: Rhinebothriidea) parasitic in Australian stingrays (Elasmobranchii: Batoidea)

Cestodes of Pseudobatos horkelii (Mller and Henle) (Rhinopristiformes) including Rhinebothrium quequense n. sp. (Rhinebothriidea) and Caulobothrium pieroi n. sp. (Tetraphyllidea) from the southwestern Atlantic

Two new species of cestodes were described from the Brazilian guitarfish, Pseudobatos horkelii (Mller and Henle) (Rhinopristiformes: Rhinobatidae), from coastal waters off Argentina in the southwestern Atlantic Ocean. Rhinebothrium quequense n. sp. (Rhinebothriidea) differs from its congeners by a combination of morphological characters, including the total number of loculi, the absence of loculi at the level of bothridial constriction, the number of testes per proglottid, and the number of proglottids per worm. Caulobothrium pieroi n. sp. (Tetraphyllidea) can be distinguished from the other members of the genus by the following set of morphological features including the presence of stalked bothridia with apical sucker, the number of loculi per bothridium, the number of testes per proglottid, and the number of proglottids per worm. The discovery of R. quequense n. sp. and C. pieroi n. sp. in the Brazilian guitarfish not only increases the number of rhinebothriideans and tetraphyllideans in the southwestern Atlantic, but also expands the elasmobranchs list to include P. horkelii for the first time as a new host record for cestodes globally. In addition, this is not only the first report of a species of Rhinebothrium in rhinobatids in the region, but it is also the first Caulobothrium species infecting a rhinopristiform batoid.

Morphology and glandular composition of the myzorhynchus and the remnant apical organ in adult cestodes of the order Rhinebothriidea from batoids off Argentina

The main objective of this study was to analyze the function of the myzorhynchus and remnant apical organ of adult cestodes in the order Rhinebothriidea. Several features of these structures were analyzed in 12 species belonging to six genera and two families. In particular, the glandular composition of the myzorhynchus of four species from Echeneibothriidae (i.e., Notomegarhynchus navonae and three species of Echeneibothrium) was studied using histochemical techniques and/or transmission electron microscopy. In addition, the presence of a remnant apical organ and its glandular composition were analized in six species of Rhinebothriidae and in two species of Semiorbiseptum, whose familial assignment is uncertain. We also evaluated the importance of these characters for diagnosis. The same type of gland cell was found in the myzorhynchus of Echeneibothrium species and in the remnant apical organ of Semiorbiseptum species. These gland cells were Coomassie brilliant blue-positive, periodic acid Schiff-positive and Alcian blue-negative, consistent with a glycoprotein secretion possibly involved in adhesion to the host mucosa and proteolysis. The type of gland cells found in the myzorhynchus of N. navonae were Coomassie brilliant blue-negative, periodic acid Schiff-positive and Alcian blue-positive, consistent with the production of adhesive and protective substances. The type of gland cells in the myzorhynchus and in the remnant apical organ could be a useful character for the generic diagnosis of Echeneibothrium and Semiorbiseptum, respectively. A remnant apical organ was only found in Semiorbiseptum, with its presence/absence being important as a diagnostic character at the generic level for Semiorbiseptum, Scalithrium, and Rhinebothroides. A secondary objective was to characterize the microthrix pattern of the myzorhynchus of N. navonae. An extended distribution of spinitriches was detected, which may allow a better adhesion of this large species to the host mucosa, as the main function of spinitriches is presumably that of adhesion.

Comparative Characterization of Mitogenomes From Five Orders of Cestodes (Eucestoda: Tapeworms)

The recognized potential of using mitogenomics in phylogenetics and the more accessible use of high-throughput sequencing (HTS) offer an opportunity to investigate groups of neglected organisms. Here, we leveraged HTS to execute the most comprehensive documentation of mitogenomes for cestodes based on the number of terminals sequenced. We adopted modern approaches to obtain the complete mitogenome sequences of 86 specimens representing five orders of cestodes (three reported for the first time: Phyllobothriidea, “Tetraphyllidea” and Trypanorhyncha). These complete mitogenomes represent an increase of 41% of the mitogenomes available for cestodes (61–147) and an addition of 33% in the representativeness of the cestode orders. The complete mitochondrial genomes are conserved, circular, encoded in the same strand, and transcribed in the same direction, following the pattern observed previously for tapeworms. Their length varies from 13,369 to 13,795 bp, containing 36 genes in total. Except for the Trypanorhyncha specimen, the gene order of the other four cestode orders sequenced here suggests that it could be a synapomorphy for the acetabulate group (with a reversion for taenids). Our results also suggest that no single gene can tell all the evolutionary history contained in the mitogenome. Therefore, cestodes phylogenies based on a single mitochondrial marker may fail to capture their evolutionary history. We predict that such phylogenies would be improved if conducted under a total evidence framework. The characterization of the new mitochondrial genomes is the first step to provide a valuable resource for future studies on the evolutionary relationships of these groups of parasites.

Two new species of Scalithrium (Cestoda: Rhinebothriidea) from rajiform batoids of the Argentine Sea

Two new species of Scalithrium Ball, Neifar Euzet, 2003 were found in rajiform batoids of the Argentine Sea: Scalithrium kirchneri sp. nov., parasite of the Rio skate Rioraja agassizii (Mller Henle) from waters off Buenos Aires Province, and Scalithrium ivanovae sp. nov., parasite of the La Plata skate Atlantoraja platana (Gnther) from waters off Ro Negro Province. Scalithrium kirchneri sp. nov. and S. ivanovae sp. nov. differ from their congeners by having a particular combination of features including: total length, number of loculi on the distal bothridial surface, absence of bilobed bothridia and number of testes. Additionally, S. kirchneri sp. nov. can be distinguished from S. ivanovae sp. nov. by the presence of a vaginal sphincter and seminal receptacle, by the position of the entrance of the vas deferens into the cirrus sac, and by the microthrix pattern on the proximal bothridial surface. Based on this and previous studies, we conclude that some morphological traits may not be considered as key characters for the generic diagnosis of Scalithrium due to their variability within the genus. These characters include the musculature disposition in bothridial transverse septa and position of the entrance of the vas deferens into the cirrus sac, which certainly complement other diagnostic characters at a specific level. The discovery of these two species represents the first record of the genus Scalithrium in temperate waters of the Southern Hemisphere. In addition, this study is the first to undoubtedly identify batoids from the order Rajiformes as hosts for Scalithrium.

Three New Species of Rhinebothrium (Cestoda: Rhinebothriidea) from the Leopard Whipray, Himantura Leoparda, in Australia

Examination of 4 specimens of the leopard whipray Himantura leoparda, a dasyatid stingray from northern Australia, led to the discovery of 3 new species of Rhinebothrium. Rhinebothrium leopardensis n. sp., Rhinebothrium nandoi n. sp., and Rhinebothrium ruhnkei n. sp. are described, increasing the diversity of the genus to 51 species globally. All 3 new species differ from their congeners in terms of testis number, proglottid number, loculus number, and size. With respect to one another, R. leopardensis n. sp. has bothridia that are weakly constricted at their centers and has a greater number of proglottids than the other 2 species (93-108 vs. 11-15, and 48-78, respectively). Rhinebothrium nandoi n. sp. is the smallest of the 3 species found in H. leoparda (3.6-5 vs. 10-15 mm and 10.1-15.8 mm in total length [TL], respectively) and bears bothridia that are constricted at their centers. Rhinebothrium ruhnkei n. sp. bears bothridia that are conspicuously constricted at their centers and has more testes than R. leopardensis and fewer than R. nandoi (7-10 vs. fewer than 7 and 21-33, respectively). Before this study, 56% (27 of 48) of Rhinebothrium species had been described from the freshwater river systems of South America and the marine waters surrounding South and North America. In contrast, despite the remarkably diverse nature of its batoid fauna, only 19 species were known from the Indo-Pacific region. Our work increases this number to 22, emphasizing the highly underestimated nature of Rhinebothrium diversity in this region of the globe. The discovery of these 3 new species was not unexpected, given the relatively poor status of our current knowledge of the cestode faunas of dasyatid stingrays in the Indo-Pacific region, and given the fact that it is common for a single batoid species to host 2 or more species of Rhinebothrium. Our results suggest that additional work on the cestode faunas of the batoids, especially dasyatids, from the Indo-Pacific region is likely to be highly productive in terms of contributing to the knowledge of Rhinebothrium diversity.

The First Report and Description of a New Species of Rhinebothrium from a Dasyatid Stingray from the Brazilian Northeastern Coast with a Review of the Distribution of the Genus throughout Endemic Marine Ecoregions

Here we describe a new species of RhinebothriumLinton, 1890, from Hypanus guttatus (Bloch and Schneider). Rhinebothrium ramosi n. sp. can be differentiated from all 51 valid species of the genus by having 4-5 testes and uterus that extends throughout the entire length of the proglottid. Only 8 of the above species closely resemble R. ramosi in total length (Rhinebothrium bunburyense, Rhinebothrium chollaense, Rhinebothrium corbatai, Rhinebothrium dasyatidis, Rhinebothrium kruppi, Rhinebothrium lintoni, Rhinebothrium margaritense, and Rhinebothrium reydai). Despite the resemblance, R. bunburyense, R. corbatai, R. dasyatidis, R. lintoni, and R. margaritense can be distinguished from the new species by possessing a larger number of proglottids. The remaining 3 species (R. chollaense, R. kruppi, and R. reydai) overlap in total length and number of proglottids with R. ramosi. However, they can be distinguished from the new species by possessing a single posterior-most bothridial loculus instead of arranged as a pair, as found in the new species. This is the first report of the genus from the coastal waters of Brazil and brings to 52 the number of valid species for this genus. Additionally, we use the patterns of infection and distribution for species of Rhinebothrium to make predictions of expected diversity within the genus, especially for unsurveyed hosts in endemic marine ecoregions of the world.