Trypanorhynch cestodes from Indonesian coastal waters (East Indian Ocean)

Dasyrhynchus giganteus plerocercoids encysting in the musculature of Indian halibut (Psettodes erumei): seasonal prevalence, morpho-molecular characterization, and histopathological alterations

This study investigated the prevalence, morphology, molecular identification, and histopathological effects of larval tapeworms (plerocercoids) infecting the skeletal muscles of the Indian halibut (Psettodes erumei) collected from the coastal waters of the Arabian Gulf. Numerous oval or round blastocysts, measuring 13-26 mm, were found embedded within the muscular tissues of the Indian halibut, rendering the fish unsuitable for human consumption. Morphological and molecular analyses identified the plerocercoids as Dasyrhynchus giganteus (family Dasyrhynchidae), with an overall prevalence of 15.4%. The seasonal prevalence was the highest in summer (14.6%), followed by spring (10.6%), winter (4.4%), and autumn (3.5%). Infection rates increased with fish size. Histopathological examination revealed fibrous connective tissue capsules surrounding the larvae, causing muscular atrophy and degenerative changes, with few inflammatory eosinophilic cells. Molecular and phylogenetic analysis of the 28S rDNA gene sequences confirmed the specimens as D. giganteus, clustered closely with other sequences of D. giganteus with 100% bootstrap values. This study provided valuable insights into the parasitic infection dynamics, seasonal variation, molecular identification, and histopathological effects, highlighting the importance of monitoring fish for food safety and public health implications.

Larvae trypanorhynch (Cestoda) infecting the dusky flounder, Syacium papillosum (Paralichthyidae: Pleuronectiformes) in the continental shelf of the Yucatan Peninsula, Mexico

Trypanorhynch cestode larvae were found parasitizing specimens of dusky flounder Syacium papillosum (Linnaeus, 1758) in the Southeastern Gulf of Mexico (s-GoM). Plerocercoids were recovered from a total of 194 flatfish, embedded in the intestine and stomach wall. Trypanorhynch were identified using morphology and a molecular phylogeny using newly sequenced partial 28S (region D1-D3) ribosomal DNA in combination with data derived from other species of trypanorhynchs available from GenBank. Larvae representing three genera of trypanorhynch cestodes, Nybelinia Poche, 1926; Kotorella Euzet & Radujkovic, 1989 and Oncomegas Dollfus, 1929 were found in dusky flounder specimens in the s-GoM. These plerocercoids represent six species: Nybelinia sp. 1, Nybelinia sp. 2, Nybelinia sp. 3, Nybelinia sp. 4, Kotorella pronosoma (Stossich, 1901) and Oncomegas wageneri (Linton, 1890) Dollfus, 1929. All cestode specimens in this study represent new locality records for their respective species.

A Study on the Pathological Effects of Trypanorhyncha Cestodes in Dusky Groupers Epinephelus marginatus from the Canary Islands

Simple Summary

Trypanorhyncha are common parasites of marine fish. Despite numerous studies detailing their biology, knowledge on the effects caused by these parasites in fish tissues is still limited. Dusky groupers are keystone species, necessary for the preservation of several marine ecosystems. Considering their vulnerable state of conservation and the efforts being made to culture them, identification of the effects caused by Trypanorhyncha is vital. Here, we have assessed the prevalence of Trypanorhyncha in dusky groupers from the Canary Islands and the associated pathological changes. Of the 28 fish examined, 27 presented trypanorhynch larvae. Macroscopically, in the abdominal cavity, there were numerous larvae-filled cysts and nodules embedded in abundant fibrosis, hindering the separation of the organs. Microscopically, in the peritoneum, stomach and intestine, there were numerous degenerated parasitic cysts and extensive deposition of fibrous connective tissue with minimal inflammatory responses. This study shows that Trypanorhyncha are common parasites of adult dusky groupers from the Canary Islands. Even though the immune system appears to isolate and eliminate the parasites, extensive fibrosis may have a detrimental impact on fish health when adjacent organs are compressed and their functions impaired.

Abstract

Trypanorhyncha are cestodes commonly infecting marine fish. Numerous studies have detailed the biology of Trypanorhyncha species, but information on the pathological changes produced by these parasites is limited. Dusky groupers are keystone species necessary for the preservation of several marine ecosystems. Considering their vulnerable state of conservation and the efforts being made to culture them, identification of the effects caused by Trypanorhyncha is vital. Here, we aimed to determine the prevalence and pathological changes produced by Trypanorhyncha in dusky groupers from the Canary Islands. The prevalence of trypanorhynch plerocerci was 96%. Grossly, in the abdominal cavity, there were numerous larvae-filled cysts and nodules. These were embedded in abundant fibrosis, producing visceral adhesions. Histologically, affecting the peritoneum, stomach, and intestine there were numerous degenerated encysted plerocerci and extensive deposition of mature connective tissue. These findings indicate that Trypanorhyncha is highly prevalent in adult dusky groupers from the Canary Islands, producing a progressive and chronic response. Furthermore, fish immune system appears to attempt to eliminate the parasites through fibrous encapsulation. Nonetheless, extensive fibrosis may have a detrimental impact on fish health when adjacent cells or tissues are compressed and their functions impaired.

Ultrastructure of the rhyncheal apparatus and other structures of the scolex of Grillotia (Christianella) carvajalregorum (Cestoda: Trypanorhyncha)

The scolex ultrastructure was studied in Grillotia (Christianella) carvajalregorum (Cestoda: Trypanorhyncha) using histochemistry and transmission electron microscopy. We show for the first time the presence of scolex glands arranged in two longitudinal acini at the pars vaginalis parenchyma. These glands, along with those scattered in bothrial parenchyma, produce potentially adhesive glycoprotein secretions that are discharged via ducts to the bothrial grooves and apex. A particular type of sensory receptor was found around frontal gland pores, with a possible function in regulating their secretion activity. The internal structure of microtriches varies according to their morphotype and distribution on the scolex, this study providing the first description of the ultrastructure of serrate lanceolate spinitriches. The projections that form serrate margins are an extension of the medulla, differing from similar projections of other spinitriches. The large caps observed in serrate lanceolate spinitriches may reflect their specialization in attachment to and abrasion of intestinal mucosa, while the short caps and large bases of acicular filitriches may reflect their involvement in nutrient absorption. We also describe the rhyncheal apparatus ultrastructure, showing a similar basic structure of tentacular walls than that of other trypanorhynchs. Some differences among species in the number of fibrous layers, composition of the apical cytoplasm and presence of microvilli-like projections were discussed. Finally, our study describes in detail the internal ultrastructure of hollow hooks, evidencing the presence of cytoplasm, mitochondria and fibrils. The location of these fibrils may increase the area of contact surface of hooks on tentacles, possibly allowing for a higher tensile strength than that of solid hooks. We consider that gland location and shape, composition of tentacular wall layers, and hook internal structure may serve as useful characters for the taxonomy and phylogeny of Trypanorhyncha. RESEARCH HIGHLIGHTS: This is the first description of scolex internal ultrastructure in Grillotia carvajalregorum, showing the presence of glands arranged in two longitudinal acini at the pars vaginalis parenchyma, with potentially adhesive functions. The internal ultrastructure of serrate lanceolate spinitriches and acicular filitriches may reflect their specialization in attachment to the host intestinal mucosa and their involvement in nutrient absorption, respectively. Internally, hollow hooks have cytoplasm with mitochondria and fibrils, which are more widely distributed than in solid hooks, possibly increasing their tensile strength.

Phylogenetic placement and microthrix pattern of Paranybelinia otobothrioides Dollfus, 1966 (Trypanorhyncha) from krill Nyctiphanes simplex Hansen, 1911

Plerocerci of the monotypic Paranybelinia otobothrioides were found parasitizing the subtropical neritic krill Nyctiphanes simplex in the Gulf of California, Mexico. The plerocerci were recovered from two microhabitats of the intermediate host, typically embedded inside the digestive gland (hepatopancreas) or rarely in the hemocoel. The morphology of the simple, single-layered blastocyst surrounding the entire scolex is unique within the Trypanorhyncha by having four large funnel-like pori or openings possibly with feeding and/or excretory function. One of the openings is located anteriorly and three at the posterior end. Scolex surface ultrastructure shows hamulate and lineate spinitriches covering the bothrial surface, capilliform filitriches at the anterior scolex end and on the scolex peduncle, and short papilliform filitriches on the long appendix. This pattern resembles that of species of the Tentaculariidae; but differs in that the hamulate spinitriches, which appear lineate at the bothrial margins, densely cover the entire distal bothrial surface. Tegumental grooves are present on the posterior bothrial margin, lacking spinitriches. Paranybelinia otobothrioides and Pseudonybelinia odontacantha share the following unique combination of characters: two bothria with free lateral and posterior bothrial margins, homeoacanthous homeomorphous armature, tegumental grooves, the distribution of the hamulate spinitriches, and the absence of prebulbar organs. Both genera infect euphausiids as intermediate hosts. Sequence data of the partial ssrDNA gene place Pa. otobothrioides sister to the family Tentaculariidae, and the Kimura two-parameters (K2P) distance between Pa. otobothrioides and species of the family Tentaculariidae ranged from 0.027 to 0.039 (44-62 nucleotide differences). These data suggest both species be recognized in a family, the Paranybeliniidae, distinct from, albeit as sister taxon to, the Tentaculariidae. High prevalence of infection (<14%) and ontogenetic changes of Pa. otobothrioides support N. simplex as a required intermediate host and suggest a zooplanktophagous elasmobranch as final host in the Gulf of California.

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First description of the microthrix pattern of Paranybelinia otobothrioides Dollfus (1966) larva.

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The krill Nyctiphanes simplex is the first known host of larvae of P. otobothrioides.

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Blastocyst morphology surrounding the scolex is unique within the Trypanorhyncha.

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SsrDNA sequence places P. otobothrioides as sister taxon to the Tentaculariidae.

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We emmend the superfamily diagnosis in the most recent classification.

Morphological and molecular insights of a new species of trypanorhynchid cestode parasite, Nybelinia exostigmi, in the Narrowstripe cardinal fish Apogon exostigma

Forty specimens of the Narrowstripe cardinal fish Apogon exostigma were examined for gastrointestinal helminthes, and 62.5% were infected with a new trypanorhynchid larval cestode parasite. The morphology of its larval stage was studied based on light and scanning electron microscopy. The data revealed plerocercoid larvae characterized by a pyriform body lined with prominent microtriches; the acraspedote scolex had four overlapping bothridia; four tentacles protruded through the pars bothridialis; the armature of the tentacles was homeocanthous, homeomorphous, and consisted of falcate compact rose-thorn-shaped tentacular hooks; four oval-shaped bulbs in pars bulbosa; and short appendix at terminal end of the body. Molecular analysis of the 18S rRNA sequences verified the taxonomy of this parasite and supported its morphology. We discovered that there was a close identity (up to 87%) with alternative species obtained for comparison from GenBank. The data also showed that there were high blast scores and low divergence values between this parasite and other Tentaculariidae species. The phyletic analysis showed that parasite sequences in conjunction with existing data places this trypanorhynchid species among the Tentaculariidae. This species is deeply embedded within genus Nybelinia with close relationships to Nybelinia queenslandensis as a putative sister taxon.

A new genus and species of the trypanorhynch family Otobothriidae Dollfus, 1942 from the slender weasel shark Paragaleus randalli Compagno, Krupp & Carpenter (Hemigaleidae) in the Persian Gulf

A survey on the cestode fauna of Paragaleus randalli Compagno, Krupp & Carpenter in the Persian Gulf resulted in the discovery of a new trypanorhynch species of the family Otobothriidae Dollfus, 1942, the second otobothrioid species hosted by the family Hemigaleidae Hasse. The new species exhibits the closest morphological similarity to Pristiorhynchus palmi Schaeffner & Beveridge, 2013, the type- and only species of its genus. However, the new species differs from P. palmi in the position of the bothrial pits, the morphology and oncotaxy of the basal armature, the commencement of the hook files on the internal surface, a wider scolex peduncle in the pars bulbosa than in the pars vaginalis, a long neck and the presence of a lateral bothrial groove connecting the two bothrial pits to each other. The latter character is a unique trait within the Otobothrioidea Dollfus, 1942. Considering such differences, a new genus, Olgaella n. g., was erected to accommodate O. elenae n. g., n. sp. within the Otobothriidae. The evolutionary relatedness of the bothrial pits of the Otobothrioidea and the bothrial grooves of the Lacistorhynchoidea Guiart, 1927 is discussed.

Parasites of the grouper fish Epinephelus coioides (Serranidae) as potential environmental indicators in Indonesian coastal ecosystems

A total of 195 Epinephelus coioides (Hamilton, 1822) were studied for fish parasites from Javanese (Segara Anakan lagoon) and Balinese waters. Up to 25 different parasite species belonging to the following taxa: one Ciliata, one Microsporea, five Digenea, one Monogenea, four Cestoda, four Nematoda, one Acanthocephala, one Hirudinea and seven Crustacea were identified with four new host and locality records. The dominant parasites included the monogenean Pseudorhabdosynochus lantauensis (53.3-97.1%), the nematode Spirophilometra endangae (23.3-42.9%), the digenean Didymodiclinus sp. (2.9-40.0%), the nematodes Philometra sp. (22.6-34.3%) and Raphidascaris sp. (2.9-28.6%), and the isopod Alcirona sp. (6.7-31.4%). Regional differences for E. coioides were found in terms of endoparasite diversity, total diversity according to Shannon-Wiener, Simpson index and Evenness. A comparison with published data from Sumatera revealed highest endoparasite diversity (Shannon-Wiener: 1.86/1.67-2.04) and lowest ectoparasite/endoparasite ratio (0.73/0.57-0.88) off the Balinese coast, followed by Lampung Bay, Sumatera (1.84; 0.67), off the coast of Segara Anakan lagoon (1.71; 0.71), and in the lagoon (0.30/0.19-0.66; 0.85/0.67-1.00). The presented data demonstrate the natural range of these parameters and parasite prevalences according to habitat and region, allowing adjustment of the scale that has been used in the visual integration of the parasite parameters into a star graph. The parasite fauna of E. coioides in Segara Anakan lagoon 'improved' from 2004 until 2008/09, possibly related to earlier oil spill events in 2002 and 2004. The use of grouper fish parasites as an early warning system for environmental change in Indonesian coastal ecosystems is discussed.

Redescriptions and new records of species of Otobothrium Linton, 1890 (Cestoda: Trypanorhyncha)

Redescriptions are provided for five incompletely described species of Otobothrium Linton, 1890: Otobothrium alexanderi Palm, 2004 from two species of carcharhinid sharks, Carcharhinus cautus (Whitley) and C. melanopterus (Quoy & Gaimard) at three localities off northern Australia; O. australe Palm, 2004 based on material collected from the type-host and type-locality and from six additional myliobatid and carcharhinid host species off Western Australia, the Northern Territory and northern Queensland; O. insigne Linton, 1905 from Rhizoprionodon terraenovae (Richardson) and Sphyrna tudes (Valenciennes) in the Atlantic Ocean off Senegal and the Democratic Republic of the Congo; O. mugilis Hiscock, 1954, previously known only from larval stages, based on adults from five sphyrnid and carcharhinid definitive host species off northern Australia and Malaysian Borneo; and O. penetrans Linton, 1907 from material collected from two species of hammerhead sharks (Sphyrnidae) in the Red Sea off Jordan and the Indian Ocean off Western Australia. Additional host and locality records are added for the type-species, O. crenacolle Linton, 1890 and for O. carcharidis (Shipley & Hornell, 1906). Two descriptions are provided for Otobothrium spp. treated here as Otobothrium sp. 1 from C. melanopterus off northern Australia and Otobothrium sp. 2 from Sphyrna zygaena (Linnaeus) in the Gulf of California, Mexico.

An environmental assessment of the parasite fauna of the reef-associated grouper Epinephelus areolatus from Indonesian waters

Sixty Epinephelus areolatus were examined for metazoan fish parasites in Indonesia, off Segara Anakan lagoon, Java and in Balinese waters. The study revealed 21 different parasite species, and 14 new host and locality records. The anisakid nematodes Anisakis typica and, for the first time in Indonesia, Anisakis sp. HC-2005 were identified by using molecular methods. Ecological parameters were calculated for both sites off the anthropogenically influenced Segara Anakan lagoon and the relatively undisturbed reference site at the southern Balinese coast. The fish from Segara Anakan demonstrated a significantly higher enzymatic activity (Hepatosomatic index) and a significantly reduced number of heteroxenous gut helminths (e.g. the digenean Didymodiclinus sp., the nematode Raphidascaris sp. and the acanthocephalan Serrasentis sagittifer). Other regional differences for E. areolatus included ecto-/endoparasite ratio, endoparasite diversity, the parasite species composition and prevalence of infection of the respective parasite species. We applied the stargraph method to visualize observed regional differences using grouper parasites as biological indicators for the sampled coastal ecosystems at both sampling sites.

Parasite diversity as an indicator of environmental change? An example from tropical grouper (Epinephelus fuscoguttatus) mariculture in Indonesia

Fish parasites are used to monitor long-term change in finfish grouper mariculture in Indonesia. A total of 210Epinephelus fuscoguttatuswere sampled in six consecutive years between 2003/04 and 2008/09 and examined for parasites. The fish were obtained from floating net cages of a commercially run mariculture facility that opened in 2001. The fauna was species rich, consisting of ten ecto- and 18 endoparasite species. The ectoparasite diversity and composition was relatively stable, with the monogeneansPseudorhabdosynochusspp. (83–100% prevalence, Berger-Parker Index of 0·82–0·97) being the predominant taxon. Tetraphyllidean larvaeScolex pleuronectisand the nematodesTerranovasp. andRaphidascarissp. 1 were highly abundant in 2003/04–2005/06 (max. prevalenceS. pleuronectis40%,Terranovasp. 57%,Raphidascarissp. 1 100%), and drastically reduced until 2008/09. These parasites together with the prevalence ofTrichodinaspp., ecto-/endoparasite ratio and endoparasite diversity illustrate a significant change in holding conditions over the years. This can be either referred to a definite change in management methods such as feed use and fish treatment, or a possible transition of a relatively undisturbed marine environment into a more affected habitat. By visualizing all parameters within a single diagram, we demonstrate that fish parasites are useful bioindicators to monitor long-term change in Indonesian grouper mariculture. This also indicates that groupers can be used to monitor environmental change in the wild. Further taxonomic and systematic efforts in less sampled regions significantly contributes to this new application, supporting fish culture and environmental impact monitoring also in other tropical marine habitats.

Trypanorhynch cestodes of teleost fish from the Persian Gulf, Iran

A total of 299 fish belonging to ten teleost species were studied in Iranian waters at the north-eastern coast of the Persian Gulf for larval trypanorhynch cestode infection. The following trypanorhynch species were identified: Callitetrarhynchus gracilis Pintner, 1931, Pseudogilquinia thomasi (Palm, 2000), Pterobothrium lesteri Campbell and Beveridge, 1996 and Pseudolacistorhynchus shipleyi (Southwell, 1929). The most abundant parasite was C. gracilis which was isolated from seven teleost species. The highest prevalence (62.9%) and dominance (0.98) were demonstrated for P. thomasi with a maximum intensity of 22 in Indian halibut Psettodes erumei. Collections of P. lesteri and P. shipleyi from the Persian Gulf represent new locality records, thus extending the known range of distribution for both species. Four new host records are established. The recorded combination of trypanorhynch species and the established host range correspond to other regions, such as off the Brazilian coast. In terms of species distribution, the north-western part of the Indian Ocean, together with the Gulf of Bengal and the Indonesian archipelago, share the same species, resulting from connected water bodies. All trypanorhynch species were isolated from the body cavity, except for P. thomasi which was recorded from the musculature of P. erumei. Relatively high intensities of infection in P. erumei may be of public health concern in the region, necessitating the consumption of well-cooked fish products.

A new approach to visualize ecosystem health by using parasites

A new approach is chosen to visualize ecosystem health by using parasite bioindicators in Segara Anakan Lagoon, a brackish water ecosystem at the southern Java coast, Indonesia. Three fish species (Mugil cephalus, Scatophagus argus, Epinephelus coioides) were collected in two different years and sampling sites and studied for ecto- and endoparasites. Additional data were taken for E. coioides from two further sites in Lampung Bay, Sumatra, and for E. fucoguttatus out of floating cages from a mariculture facility in the Thousand Islands, Jakarta Bay, North Java. The parasite fauna of fishes inside the lagoon was characterized by a high number of ecto- and a low number of endoparasites, the endoparasite diversity was relatively low and the prevalence of ectocommensalistic trichodinid ciliates was high. These parameters were chosen to indicate the biological conditions inside the lagoon. In E. coioides during rainy season, the prevalence of trichodinid ciliates was highest inside the lagoon (55%) compared with 27% in an open-net-cage mariculture and 5.7% in free-living specimens in Lampung Bay. The endoparasite diversity (Shannon-Wiener) was lowest in fish from Segara Anakan lagoon (0.66) compared with fish from an open-net-cage mariculture (0.71) and free-living specimens (1.39). Results for E. fuscoguttatus from the mariculture site in the Thousand Islands, a relatively undisturbed marine environment, demonstrated high parasite diversity (1.58) in the cultivated fish, a high number of endoparasites, and no trichodinids. A star graph is used to visualize the parasite composition for the different fishes, sampling sites, and conditions, using (1) the prevalence of trichodinid ciliates, (2) the ecto/endoparasite ratio and (3) the endoparasite diversity as bioindicators. The application of the star graph is suggested to be a suitable tool to visualize and monitor environmental health under high parasite biodiversity conditions within tropical ecosystems. It can also support a better communication to stake holders and decision makers in order to monitor environmental impact and change.

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.

Crustacean fish parasites from Segara Anakan Lagoon, Java, Indonesia

The present study is the first investigation on ectoparasites of commercial important fish from Segara Anakan, a brackish water lagoon located at the southern coast of Java, Indonesia. Eight economically important marine fish species (Mugil cephalus, Siganus javus, Scatophagus argus, Caranx sexfasciatus, Lutjanus johnii, Eleutheronema tetradactylum, Johnius coitor, and Epinephelus coioides) were examined for crustacean parasites. Prevalence and intensity data for each parasite species are given, together with an analysis of the origin and possible transmission pathways. A highly divers copepod fauna consisting of 23 different species and two isopods was found. All fish species were at least infested with two copepod species, with the exception of L. johnii, S. argus, and M. cephalus. With seven and six species, respectively, they harboured the most species-rich ectoparasite fauna. The copepods Ergasilus sp. 3 and Caligus acanthopagri on S. argus showed the highest prevalence (78.6) and intensity [17.8 (1-233) and 5.3 (1-22)] of infestation. The recorded parasite fauna is represented by marine, brackish water, and probably also freshwater components. The brackish water environment of Segara Anakan does not prevent disease outbreaks due to parasitic copepods by preventing pathogenic marine or freshwater species to enter the lagoon. This might cause fish health problems if the Segara Anakan Lagoon would be developed for finfish mariculture in future.

A revision of Microbothriorhynchus Yamaguti, 1952 (Cestoda: Trypanorhyncha), with the redescription of M coelorhynchi Yamaguti, 1952 and the description of M reimeri n sp

The genus Microbothriorhynchus Yamaguti, 1952 is revised. Plerocerci of M. coelorhynchi Yamaguti, 1952 from the body-cavity of Brotula barbata (Bloch & Schneider) off the Angolan coast are re-described, and M. reimeri n. sp. from the body-cavity of Helicolenus maculatus (Cuvier) and Caelorinchus parallelus (Günther) from coastal waters off Mozambique is added to the genus. Both species are characterised in having an elongated, slightly craspedote scolex with small, collar-like bothridia, an elongate pars vaginalis and very long bulbs. The tentacular armature is heteroacanthous atypica, with eight principal hooks and intercalary hooks merging with a band of spiniform hooks on the external tentacle surface. The adult is unknown. Microbothriorhynchus is allocated to the Lacistorhynchidae Guiart, 1927, in having a blastocyst, two bothridia and a heteroacanthous atypica armature. Dasyrhynchus Pintner, 1928 and Pseudogrillotia Dollfus, 1969 are considered the most closely related genera, sharing characters such as the craspedote scolex, similar scolex proportions and hook patterns. Microbothriorhynchus appears to link the heteroacanthous atypica genera Grillotia Guiart, 1927 and Pseudogrillotia with the poeciloacanthous genus Dasyrhynchus.