GALAXITAENIA TOLOI N. GEN., N. SP. (EUCESTODA: PSEUDOPHYLLIDEA) FROM GALAXIAS PLATEI (PISCES: OSMERIFORMES, GALAXIIDAE), IN THE PATAGONIAN REGION OF ARGENTINA

First Freshwater Bothriocephalidean (Cestoda) from Tropical South America, Closely Related to African Taxa

Regobothrium microhamulinum n. gen. and n. sp. (Bothriocephalidea: Bothriocephalidae) is proposed to accommodate a new cestode from flatfish Catathyridium jenynsii (Chabanaud, 1922) (Pleuronectiformes: Acharidae; type host) and another 3 freshwater fishes of the orders Characiformes, Cyprinodontiformes, and Siluriformes in the Neotropical Region. The new genus is placed in the Bothriocephalidae because it possesses medioventral uterine and mediodorsal genital pores and a follicular vitellarium. Regobothrium n. gen. is characterized by possessing a tiny, slightly subovate scolex narrower than the strobila, with an apical disc armed with 2 semicircles of 15-17 tiny hooks in each and an acraspedote strobila. Regobothrium n. gen. differs from all bothriocephalid cestodes that have a scolex armed with hooks by their small size (maximum length less than 20 μm) and a triangular shape with the basal part (handle or basal plate) shorter than the distal coniform part (blade). In the other hooked bothriocephalids, hooks have a longer handle than a blade. Regobothrium microhamulinum n. gen. and n. sp. is the third bothriocephalidean cestode described from freshwater teleosts in South America but the first out of Patagonia. Molecular phylogenetics consider Regobothrium as a member of a lineage consisting of (up to now exclusively) freshwater bothriocephalids from the Ethiopian biogeographic region, thus indicating Gondwanan relationship.

Annotated checklist of fish cestodes from South America

An exhaustive literature search supplemented by a critical examination of records made it possible to present an annotated checklist of tapeworms (Cestoda) that, as adults or larvae (metacestodes), parasitize freshwater, brackish water and marine fishes, i.e. cartilaginous and bony fishes, in South America. The current knowledge of their species diversity, host associations and geographical distribution is reviewed. Taxonomic problems are discussed based on a critical evaluation of the literature and information on DNA sequences of individual taxa is provided to facilitate future taxonomic and phylogenetic studies. As expected, the current knowledge is quite uneven regarding the number of taxa and host-associations reported from the principal river basins and marine ecoregions. These differences may not only reflect the actual cestode richness but may also be due to the research effort that has been devoted to unravelling the diversity of these endoparasitic helminths in individual countries. A total of 297 valid species, 61 taxa identified to the generic level, in addition to unidentified cestodes, were recorded from 401 species of fish hosts. Among the recognized cestode orders, 13 have been recorded in South America, with the Onchoproteocephalidea displaying the highest species richness, representing c. 50% of all species diversity. The majority of records include teleost fish hosts (79%) that harbour larval and adult stages of cestodes, whereas stingrays (Myliobatiformes) exhibit the highest proportion of records (39%) among the elasmobranch hosts. Fish cestodes are ubiquitous in South America, being mostly recorded from the Warm Temperate Southeastern Pacific (WTSP; 31%) for marine hosts and the Amazon River basin (45%) for freshwater ones. The following problems were detected during the compilation of literary data: (i) unreliability of many records; (ii) poor taxonomic resolution, i.e. identification made only to the genus or even family level; (iii) doubtful host identification; and (iv) the absence of voucher specimens that would enable us to verify identification. It is thus strongly recommended to always deposit representative specimens in any type of studies, including faunal surveys and ecological studies. An analysis of the proportion of three basic types of studies, i.e. surveys, taxonomic and ecological papers, has shown a considerable increase of ecological studies over the last decade.

A new species of Bothriocephalus Rudolphi, 1808 (Eucestoda: Bothriocephalidea) from the channel bull blenny Cottoperca gobio (Günther) (Perciformes: Bovichtidae) on the Patagonian shelf off Argentina

Bothriocephalus timii n. sp. is the first tapeworm species reported from a bovichtid fish. The new species was commonly found (prevalence 85%) in the intestine of Cottoperca gobio (Günther) collected on the Patagonian shelf off Argentina. It is characterised by a strobila with segments and proglottides usually longer than wide, having posterolateral wing-like expansions with a medial notch on both the dorsal and ventral surfaces; a scolex with an apical disk; elongate bothria opening posteriorly, with laterally and longitudinally extended convex lappets; testes 42-185 in number, in one layer, arranged in two lateral continuous bands along the strobila; an elongate cirrus-sac, situated obliquely, with the proximal part curved anteriolaterally; and an ovary which is usually butterfly-shaped. The new species is morphologically similar to B. bengalensis Devi, 1975 from Carangoides plagiotaeniata Bleeker, B. branchiostegi Yamaguti, 1952 from Branchiostegus japonicus Houttuyn, B. carangis Yamaguti, 1968 from C. ferdau Forsskål and B. gadellus Blend & Dronen, 2003 from Gadella imberbis (Vaillant) based on the presence of posterolateral wing-like expansions with a medial notch on dorsal and ventral surfaces of segments and proglottides along the strobila. Bothriocephalus timii n. sp. differs from B. bengalensis, B. branchiostegi and B. carangis in the absence of a vaginal sphincter and from B. gadellus in the number of testes and the size of scolex. Unpublished molecular data suggest that B. timii is most closely related to B. australis Kuchta, Scholz & Justine, 2009 from Platycephalus spp. and B. scorpii (Müller, 1776) from Myoxocephalus scorpius (Linnaeus). The genus Indobothrium Sedova & Gulyaev, 2009 is herein considered a junior synonym of Bothriocephalus Rudolphi, 1808.

Ultrastructure of the proglottid tegument (neodermis) of the cestode Echinophallus wageneri (Pseudophyllidea: Echinophallidae), a parasite of the bathypelagic fish Centrolophus niger

Ultrastructural data are provided on the tegument (or neodermis) of proglottids of the cestode Echinophallus wageneri Monticelli, 1890, the first representative of the family Echinophallidae (Pseudophyllidea), parasites of bathypelagic fish, studied using transmission and scanning electron microscopy. The surface of the ventral concave side of proglottids is covered with filiform microtriches about 1.7 microm long. Their glycocalyx, although very thick, is less extensively developed compared to that on digitiform microtriches localized on the dorsal side of the proglottids, which is also covered with filiform microtriches. The digitiform microtriches of the convex dorsal side are about 0.6 microm long, with a very short, rounded spine and the extraordinarily extensive glycocalyx seen as flocculent material. Short digitiform microtriches of E. wageneri seem to differ from microthrix types previously reported in other cestodes by transmission electron microscopy. The posterodorsal margin of all proglottids is typical in possessing a transverse band of large spiniform, tusk-shaped microtriches with a very long spine (approximately 13 microm in length), merged with filiform microtriches. Marked regional differences found in the morphology and distribution of microtriches on the proglottids of E. wageneri may be related to the different functions of the individual parts of the strobila because of the curling of the tapeworm body within the intestine of its fish host.

Ailinella mirabilis gen. n., sp. n. (eucestoda: pseudophyllidea) from Galaxias maculatus (Pisces: Galaxiidae) in the Andean-Patagonian region of Argentina

Ailinella gen. n. (Pseudophyllidea: Triaenophoridae) is proposed to accommodate Ailinella mirabilis sp. n. from Galaxias maculatus (Jenyns, 1842), a freshwater fish inhabiting the Andean lakes in Argentinean Patagonia. Ailinella belongs to the Triaenophoridae because it has a marginal genital pore, a follicular vitelline gland, and a ventral uterine pore. The new genus can be distinguished from other triaenophorids by the following combination of characters: a small body size, a low number of proglottides, which are longer than wide, a truncated pyramidal to globular scolex, a rectangular apical disc, presence of the neck, lack of internal longitudinal musculature separating the cortex from the medulla, testes distributed in one central field surrounding the ovary laterally and posteriorly, the vagina predominantly anterior to the cirrus sac, vitelline follicles circum-medullary, the genital pores post-equatorial, a saccate uterus, and operculate eggs. Blade-like spiniform microtriches were present on all tegument surfaces, and tumuli on all surfaces of the scolex and the anterior surface of the neck. Microtriches were characterized according to their size and density, and tumuli according to their size, inter-tumulus distance and density. Ailinella mirabilis is the first cestode described from G. maculatus and the second triaenophorid species recorded from a South American freshwater fish.