Brachylaima cribbi (Digenea: Brachylaimidae): scanning electron microscopical observations of the life-cycle stages

Brachylaima cribbi is a recently described species of terrestrial trematode that infects mammals and birds with helicid land snails as its first and second intermediate hosts. The adult worm is 2.5-6.0 mm long by 0.5-0.8 mm wide being a long slender cylindrical worm with oral and ventral suckers in the anterior quarter and genital pore in the posterior quarter. Scanning electron microscopy shows that there is a dense covering of tegumental spines at the anterior end which diminishes towards the posterior extremities of the worm. Development of spines was observed in juvenile and mature adult worms. In young worms 1-3 weeks post infection (wpi) spines appear as buds with a serrated edge each having 1-4 spikes per spine. As the worm ages the spines broaden and by 5 wpi the number of spikes per spine increases to an average of 8.1. The serial development of oral sucker papillae in the cercaria, metacercaria and adult worm was observed with the finding of an elongated papilla with a bifurcated tip on the cercaria becoming a shorter and thicker elongated papilla with a large central stoma on the metacercaria. In the adult worm, this papilla becomes dome-shaped with a small central stoma. For some of these papillae a cilium could be seen extended from the central stoma. Other life-cycle stages illustrated were the hatched egg with an extruded egg membrane minus an operculum and a portion of the branched sporocyst dissected from the digestive gland of the land snail Theba pisana showing a terminal birth pore. Scanning electron microscopy morphological features of the adult worm observed for the first time in a Brachylaima were the unarmed cirrus extended from the genital pore with released sperm present and the Laurer's canal opening visible in tegumental folds on the dorsal surface approximately 300 microm posterior to the genital pore.     

The susceptibility of inbred mice to infection with Brachylaima cribbi (Digenea: Brachylaimidae)

Susceptibility to infection with Brachylaima cribbi was studied in eight strains of inbred mice (AKR, C3H/HeJ, CBA/CaH, BALB/c, DBA/2J, SJL/J, A/J, C57BL/6J) and Swiss albino outbred mice by quantifying faecal egg excretion over the period of the infection. Preliminary experiments indicated that a combination of filtration/sedimentation/diethyl ether sedimentation was the most sensitive and reliable technique for quantification of eggs in faeces. Mice were infected with 13-15 wild-type B. cribbi metacercariae from naturally infected Cernuella virgata and in a second experiment with human-derived B. cribbi from laboratory-reared Helix aspersa. In both experiments C57BL/6J mice were the most susceptible having the highest egg excretion levels and the longest duration of infection. Worm burdens were assessed at 12 wpi for the wild-type and at 9 wpi for the human-derived infections, when the majority of mice were no longer excreting eggs. The numbers of worms recovered from the small intestine were few and there were no significant differences among the inbred or outbred groups of mice. We have found that C57BL/6J mice were the most susceptible to Brachylaima cribbi infection as assessed by excretion of eggs and provide a suitable model for a laboratory life-cycle.     

Introduction of a Brachylaima species (Digenea: Brachylaimidae) to Australia

A Brachylaima species recorded previously from the house mouse (Mus domesticus) in South Australia is shown to use the introduced European snails Cernuella virgata and Cochlicella barbara as first intermediate hosts, and the same two species and Theba pisana as second intermediate hosts. The life cycle is typical of Brachylaima species. The parasite is capable of infecting at least two species of native Australian rodent, Rattus fuscipes and Leporillus conditor. Because of the intermediate hosts used, it is hypothesized that this trematode species has been introduced from Europe. The parasite may be conspecific with one of a number of described European species but difficulties with the literature concerning these species have required that the present form be designated only as Brachylaima sp.     

Brachylaima phaedusae n. sp. (Trematoda: Brachylaimidae) from door snails in Japan

The metacercarial infections of door snails (Gastropoda: Clausiliidae) with unknown species of the genus Brachylaima (Trematoda: Brachylaimidae) have recently been reported in eastern Honshu and Kyushu, Japan. A large scale snail survey was carried out to clarify their taxonomic status. From the period of 2015 to 2020, a total of 1239 land snails (768 door snails and 471 others) were collected from 32 localities in Honshu, Shikoku, and Kyushu. The resulting trematode isolates were identified as Brachylaima sp. by mitochondrial DNA barcoding. The sporocysts were found only a few from Megalophaedusa sublunellata (Clausiliidae), Tauphaedusa subaculus (Clausiliidae), and Aegista trochula (Camaenidae), while the metacercariae were frequently detected from 14 species of Clausiliidae and 2 species of other families. Although Brachylaima sp. showed a broad range of intermediate hosts, door snails seem to be very important to drive the life cycle. The gravid adults of Brachylaima sp. was experimentally raised from metacercariae using immunosuppressed mice. Morphological, phylogenetical, and ecological considerations prompted us to propose Brachylaima phaedusae n. sp. for this unknown species. The definitive hosts of the new species are completely unknown. The wide geographic distribution and high genetic diversity of the new species suggest a possibility that the definitive host is ground-foraging birds, which prefer door snails.     

Zeylanurotrerna spearei sp.n. (Digenea: Brachylaimidae) from the cane toad, Bufo marinus, in Australia

Zeylanurotrema spearei sp.n. is described from the urinary bladder of the introduced cane toad, Bufo marinus , from North Queensland, Australia. The other species in Zeylanurotrema, Z.lyriocephali , has been recorded only from an agamid lizard from Sri Lanka. The new species has differently arranged gut caeca, vitelline follicles and ovary as compared with Z. lyriocephali. Z. spearei has a Laurer's canal that does not open to the exterior but which forms a glandular Juel's organ. We suggest that Z. spearei is an Australian species that has been acquired by the cane toad from a native host. In juvenile specimens of Z. spearei a persistent microcercous tail is present. From this and the anatomy of the adult we conclude that Zeylanurotrema is a brachylaimid rather than a urotrcmatid as originally proposed. A new subfamily, the Zeylanurotrematinae, is proposed to accommodate Zeylanurotrema .     

Brachylaima lignieuhadrae n. sp. (Trematoda: Brachylaimidae) from land snails of the genus Euhadra in Japan

Land snails of the genus Euhadra (Gastropoda: Bradybaenidae) are indigenous to the Japanese Archipelago. The larvae of an unknown species, tentatively named as Brachylaima sp. B (Trematoda: Brachylaimidae), have been found from Euhadra brandtii sapporo in Hokkaido, the northernmost island of Japan. In this study, a large-scale snail survey covering a wide area of Japan was conducted to confirm the larval parasite from members of Euhadra and related genera. Sporocysts with cercariae were found only from Eu. brandtii sapporo in Hokkaido and Euhadra callizona in central Honshu at low prevalence (1.0–9.6%). The metacercariae were detected widely from 6 species of Euhadra and the related genera at high prevalence (7.1–100%). A molecular identification by DNA barcoding demonstrated almost all of the larvae to be Brachylaima sp. B. Adult worms experimentally raised from the metacercariae were morphologically most similar to Brachylaima ezohelicis in Hokkaido, but could be differentiated by the microstructure of the tegumental surface. We propose Brachylaima lignieuhadrae n. sp. for the unknown species, based on the morphology, DNA profile, host specificity, and geographic distribution. Phylogeography of the new species suggests a possibility that migratory birds serve as the definitive hosts.     

Brachylaima apoplania n. sp. (Digenea: Brachylaimidae) from the Polynesian rat, Rattus exulans (Rodentia: Muridae), in New Zealand: origins and zoogeography

Brachylaima apoplania n. sp. is described from the small intestine of the Polynesian rat (Rattus exulans) on Tiritiri Matangi Island, New Zealand. The new species is most similar to Brachylaima ratti Baugh, 1962, from Rattus rattus. The two species differ only in morphometric characters, B. apoplania possessing significantly smaller suckers, pharynx, testes, ovary, and cirrus sac. The close resemblance between B. apoplania and B. ratti, the close relationship between their hosts, and archaeological evidence on the origin and early dispersal of R. exulans are used to hypothesize a common Southeast Asian origin for the 2 Brachylaima species. Brachylaima apoplania is believed to have dispersed subsequently throughout the South Pacific islands, along with its rodent host, in the canoes of the ancestors of the modern Polynesians and Maoris.     

The life-cycle of Helicometra gibsoni n. sp. (Digenea: Opecoelidae)

The life-cycle of Helicometra gibsoni n. sp., an opecoelid trematode of marine fishes, is elucidated and the life-history stages are described. Natural infections with the cercariae, which are typically opecoelid in many respects but characterised by having very long, extensile tails, were found in the intertidal snail Anachis terpsichore collected from the Lawson's Bay Coast, Bay of Bengal. Metacercariae were found in the thoracic muscles of the shooting shrimp Alphaeus malabaricus as prominent, reddish-brown, oval cysts. Laboratory experiments demonstrated that 14 days are required for the development of cercaria into the infective metacercarial stage in shrimps. Natural infections with the adult fluke were found in Scorpaenopsis cirrhosus. Therapon jarbua served as an experimental host. Fourteen-day-old metacercariae fed to T. jarbua developed into egg-producing adults in 40–43 days. Intra-specific variations noted in the flukes obtained from natural and experimental infections are presented. H. fasciata of Madhavi (1975) is regarded as a synonym of H. gibsoni.     

The life cycle of Brachylaima ruminae n. sp. (Trematoda: Brachylaimidae), a parasite of rodents

The life cycle of Brachylaima ruminae n.sp. (Trematoda: Brachylaimidae), a duodenal parasite of rodents on the Mediterranean island of Formentera (Spain) is elucidated. The new species follows a terrestrial triheteroxenous life cycle. Eggs passed in the faeces of the definitive host must be ingested by a specific first intermediate host, the land snail Rumina decollata. Branched cercariogenous sporocysts develop in the digestive gland. Microcercous cercariae come out through the terminal birth pores of the branches. Cercariae shed by the snail are terrestrial, crawling on humid substratum. They contact the second intermediate host, another land snail, principally the species R. decollata and less frequently slugs and Helicids. Cercariae enter via the excretory pore and kidney duct to their specific final location, the kidney. Unencysted metacercariae develop in the kidney (also, less frequently, in the pedal glands) to the mature, infective stage. Infective metacercariae infest the definitive host when ingested together with the snail.     

Life cycle of Brachylaima mascomai n. sp. (Trematoda: Brachylaimidae), a parasite of rats in the Llobregat delta (Spain)

The terrestrial triheteroxenous life cycle of Brachylaima mascomai n. sp. (Trematoda: Brachylaimidae) is elucidated. Operculated, assymetric, embryonated eggs (25.4 x 12.7 microm) are passed with feces of the natural (Rattus norvegicus and R. rattus) and experimental (albino and wild mice, albino rats, Apodemus sylvaticus, Mus spretus [Muridae] and the golden gerbil) definitive hosts and ingested by the helicid gastropod Pseudotachea splendida, the only natural and experimental first intermediate host. Microcaudate cercariae harbored in branched sporocysts in the digestive gland emerge from this snail and contact P. splendida, Otala punctata, Theba pisana, and Helix (C.) aspersa snails developing into unencysted infective metacercariae in the kidney. Definitive hosts are infected by ingestion of infected snails; the adult parasites inhabit the small intestine. Chaetotaxic cercarial pattern specific at acetabular (S(II) 8-10 papillae) and cephalic (C(III) 13-15 papillae, H 16 papillae) levels. Three types of cercarial papillae are observed by scanning electron microscopy (SEM) and their arrangement is correlated with chaetotaxy for the first time in trematodes: argentophilic papillae with fingerlike process (cephalic, body, and acetabular levels), argentophilic papillae with opening (2 papillae in the M body level), and nonargentophilic dome-shaped papillae (alternated with argentophilic S(II) papillae on the ventral sucker). SEM detected interlacing network of ridges covering the metacercarial body. Adults with multidigitate tegumentary spines were observed by SEM. Subequal suckers; the acetabulum located in the posterior part of anterior fifth of body. Vitellaria extend from between middle level and anterior margin of anterior testis to between middle level and posterior margin of acetabulum. Uterus almost reaches the intestinal bifurcation.     

Pholeohedra overstreeti n. g., n. sp. (Digenea: Haploporidae) from Girella zebra (Kyphosidae) in South Australia

Pholeohedra overstreeti n. g., n. sp. (Digenea: Haploporidae) is described from Girella zebra (Kyphosidae) in South Australia. The new genus is compared with all genera of Haploporidae sensu lato (including Atractotrematidae, Megasolenidae and Waretrematidae) and has a unique bell-shaped concavity at its posterior end. The genus otherwise resembles Hapladena in the arrangement of the testis, vitellarium and gut but also resembles Megasolena, Metamegasolena and Vitellibaculum except in having a single testis. This is the first haploporid reported from kyphosid fishes in Australia.     

Description and life-cycle of Thrinascotrema brisbanica n. g., n. sp. (Digenea: Plagiorchiida), a parasite of the freshwater turtle Elseya latisternum from Australia,and the erection of the family Thrinascotrematidae

A new genus and species, Thrinascotrema brisbanica, is proposed to accommodate a plagiorchiidan trematode parasitic in the stomach of the freshwater turtle Elseya latisternum. The distinctive taxonomic features of the parasite are the shape and extent of the excretory bladder, and the stenostomate arrangement of the excretory collecting ducts in the adult, cercaria and metacercaria together with a cercarial protonephridial formula of 2(12+12+12)+(12+12+12). The life-cycle is three- host and aquatic. The pulmonate snail Glyptophysa gibbosa served as both a first and second intermediate host and tadpoles of Limnodynastes peronii, Adelotus brevis and Bufo marinus, and the snail Austropeplea lessoni also served as second intermediate hosts. Eggs were fully embryonated and infective when laid, but did not hatch until eaten by the snail. Cercariae first emerged 55 days after infection at 24-28 °C. They were sluggish swimmers and survived for about 48 hr. They attached firmly to the skin of snails and tadpoles on contact and began to penetrate the skin after a short exploratory migration. Metacercariae survived in snails and tadpoles for at least 3 months. It is concluded that Thrinascotrema is best placed within a new family, the Thrinascotrematidae (Digenea: Plagiorchiida), based on the unusual morphology of the excretory system.     

Brachylaima succini sp. nov. (Trematoda: Brachylaimidae) from Succinea lauta,an amber snail in Hokkaido,Japan

Through a continuous survey of trematodes in land snails of Hokkaido, the northernmost island of Japan, we have discovered four species of the genus Brachylaima (Trematode: Brachylaimidae). Among them, Brachylaima ezohelicis, Brachylaima asakawai, and Brachylaima lignieuhadrae have already been described. Each of the three species is a strict specialist in selecting a particular species of land snail as the first intermediate host. In this report, we propose the fourth species, Brachylaima succini sp. nov., based on ecological, morphological, and phylogenetic considerations. Sporocysts and metacercariae of the new species were found exclusively from Succinea lauta, which is known as an amber snail indigenous to Hokkaido. Phylogenetic trees of nuclear 28S rDNA and mitochondrial cytochrome c oxidase subunit 1 (cox1) demonstrated it to be distinct from the other sympatric species. Although metacercariae of the new species possessed unique morphological characters, adult worms experimentally raised from the metacercariae were similar to those of B. ezohelicis and B. lignieuhadrae. Natural definitive hosts of the new species are unknown, but the existence of common cox1 haplotypes from far-distant localities suggests a possibility that birds are involved as the definitive hosts. Findings of amber snails coinfected with both sporocysts of the new species and Leucochloridium perturbatum also support the involvement of birds.     

Strzeleckia major n. g., n. sp. and S. minor n. sp. (Digenea: Hasstilesiidae) from Antechinus swainsonii (Marsupialia: Dasyuridae) in Australia

Strzeleckia major n. g., n. sp. and S. minor n. sp. are described from the dusky antechinus Antechinus swainsonii (Marsupialia: Dasyuridae) from the Kosciusko National Park in southern New South Wales, Australia. The two species were found together in the same individual host animals but occupy different sites in the intestine. The new genus is placed within the Hasstilesiidae, where it differs from the only other genus, Hasstilesia, by being more elongate and in having larger suckers, tandem testes, the ovary between rather than opposite the testes, and in having the caeca not reaching the posterior end of the body. It is suggested that the life-cycles of these species are similar to those of other hasstilesiids. Pupillid snails may act as sole intermediate hosts.     

Scorpidotrema longistipes n. g., n. sp. (Digenea: Opecoelidae) from Scorpis georgiana (Teleostei: Scorpididae) from southern Western Australia

Scorpidotrema longistipes n. g., n. sp. is described from the intestine of Scorpis georgiana Valenciennes (Scorpididae) from off Point Peron, Western Australia. The new genus is distinguished by the combination of a remarkably long and retractable ventral sucker peduncle, a possible uroproct, well-developed cirrus-sac and a uterine seminal receptacle. The subfamilial relationships of the new genus are troublesome. It incorporates features of the Opecoelinae, Stenakrinae and Plagioporinae. The absence of a canalicular seminal receptacle suggests a relationship with the Opecoelinae and Stenakrinae, whereas the well-developed cirrus-sac suggests a relationship with the Plagioporinae and Stenakrinae. The overall arrangement of the gonads is not similar to that of existing genera of Stenakrinae. It is concluded that the genus is best placed in the Stenakrinae although that subfamily may now be an artificial assemblage. This new genus forms part of a distinctive fauna of trematodes restricted to Australian southern temperate fishes.     

Renivermis crocodyli (Digenea: Exotidendriidae) n. g., n. sp. from the kidneys of the saltwater crocodileCrocodylus porosus in Australia

Renivermis crocodyli, n. g., n. sp., is described from the kidneys of the saltwater crocodileCrocodylus porosus Schneider from northern Australia. The genusRenivermis is grouped withExotidendrium Mehra, 1935 andSimhatrema Chattopadhyaya, 1970 in the family Exotidendriidae Mehra, 1935. An amended diagnosis of the family and a key to its genera are given.     

Diplobulbus brayi n. sp. (Digenea: Opecoelidae) from Odax acroptilus (Perciformes: Odacidae) off Western Australia

Diplobulbus brayi n. sp. is described from the small intestine of Odax acroptilus (Perciformes: Odacidae) from Point Peron in southern Western Australia. One of the five previously described species of Diplobulbus, D. vitellosus Bilqees, 1972 from Tetraodon lunaris (now Lagocephalus lunaris), is synonymised with Alloheterolebes indicus (Gupta, 1968) Hafeezullah, 1971, which is known from the same host in the Indian Ocean. D. brayi n. sp. can be distinguished from the remaining four species of Diplobulbus by the distinct interruption of the vitelline follicles at the ventral sucker, its more elongate form and its long post-testicular space. Diplobulbus is so far restricted to the Indo-Pacific region and appears to be stenoxenic to labroid fishes. This is the first record of a trematode from an odacid fish.     

Dactylomyza gibsoni n. g., n. sp. (Digenea: Opecoelidae) from Schuettea woodwardi (Waite) (Monodactylidae) from off Western Australia

An opecoelid digenean, Dactylomyza gibsoni n. g., n. sp. is described and figured from Schuettea woodwardi (Waite), a monodactylid from off the coast of Western Australia. The new genus conforms to the concept of the opecoelid subfamily Opecoelinae. The resemblance of the new genus to three other opecoelid genera, Pseudopecoeloides Yamaguti, 1940, Opecoeloides Odhner, 1928 and Poracanthium Dollfus, 1948, is discussed. Dactylomyza n. g. is distinguished from these morphologically similar worms on the basis of its median genital pore, ventral sucker appendages, uroproct and the absence of an accessory sucker. Pseudopecoeloides equesi Manter, 1947 is transferred to the new genus as Dactylomyza equesi (Manter, 1947) n. comb.