A new species of microphallid (Trematoda: Digenea) infecting a novel host family, the Muraenidae, on the northern Great Barrier Reef, Australia

Integrative taxonomy reveals two new species of Maritrema Nicoll, 1907 (Digenea: Microphallidae Ward, 1901), parasitizing birds in the Gulf of Mexico

Members of the genus Maritrema Nicoll, 1907 include endoparasites of aquatic birds and mammals, distributed worldwide. Adult specimens were collected from the intestines of three bird species (the great black hawks, Buteogallus urubitinga Gmelin; laughing gull, Leucophaeus atricilla Linnaeus; and the willet, Tringa semipalmata Gmelin) in three localities along the Gulf of Mexico. Photogenophores were sequenced for the large subunit (LSU) from nuclear rDNA, and the new sequences were aligned with other microphalloid sequences available in GenBank. The maximum likelihood and Bayesian inference analyses revealed three independent lineages, one corresponding to a previously described species, Maritrema corai Hernández-Orts, Pinacho-Pinacho, García-Varela & Kostadinova, 2016, and two representing two undescribed species. These two new species are described in the current study. Maritrema itzamnai n. sp. can be morphologically differentiated from its four congeneric species occurring in coastal areas of Mexico by having smaller oral (20-29 × 20-38 μm) and ventral (20-39 × 19-33 μm) suckers. In addition, Maritrema itzamnai n. sp. possess annular vitellarium instead of a horseshoe-shaped vitellarium. Maritrema kukulkanni n. sp. can be distinguished from its congeneric species reported from Mexico by possessing a larger oesophagus (44-117μm) and by having a vitellarium distributed in both the hindbody and forebody. Maritrema corai is the third species recorded in this study parasitizing the great black hawk (Buteogallus urubitinga); this represents a new host and locality record, expanding its distribution range from the Mexican Pacific Ocean to the Gulf of Mexico.

Linking metacercariae and adults of Microphallus basodactylophallus (Digenea: Microphallidae), based on larval stages from ctenophores and adult parasites from aquatic birds found in Mexico

Members of the genus Microphallus Ward, 1901, are endoparasites mainly of birds and mammals distributed worldwide. Unencysted metacercariae of Microphallus sp., were collected from the mesoglea of ctenophores of the genus Pleurobrachia Fleming; adult digeneans were recovered from the intestines of Eudocimus albus Linnaeus (Threskiornithidae) and Buteogallus urubitinga Gmelin (Accipitridae), in four locations from southeastern Mexico. Adult specimens were identified as M. basodactylophallus (Bridgman, 1969) based on the following features: body pyriform entirely covered by minute spines, prepharynx short, oesophagus very long, caeca short and widely divergent, testes slightly symmetrical and excretory vesicle short and V-shaped. Sequences from D1-D3 domain of the large subunit of ribosomal DNA (LSU) were generated, aligned, and compared with those of congeneric species available in GenBank. Phylogenetic analyses indicated that the metacercariae and adults formed a clade together with an isolate identified as M. basodactylophallus from Florida, USA (GenBank: AY220628). The intraspecific genetic divergence among isolates was low ranged from 0.0% to 0.6%, allowing the link between the two stages of the life cycle. We observed phenotypic plasticity in the morphological traits of M. basodactylophallus adults in definitive hosts (mammals and birds) throughout the distribution, which ranged from the USA to southeastern Mexico. Finally, the unencysted metacercariae identified as M. basodactylophallus represent the first report of a microphallid in ctenophores.

Description of new species of Trematoda from bats of Southeastern Mexico and a new classification for Brachylecithum rileyi n. comb. (Dicrocoeliidae)

To date, 23 species of trematodes have been reported in bats from Mexico. However, in some regions of Mexico, such as the Yucatan Peninsula, many species of bats do not have helminthological records. Here, we sampled bats in four localities in Southeastern Mexico from April 2017 to February 2022. Parasites were collected from the intestine of four species of bats: Pteronotus fulvus, Eumops nanus, Noctilio leporinus and Nyctinomops laticaudatus. Conventional morphological techniques and molecular tools with the 28S ribosomal gene were used to describe the helminths. We discovered that our parasites represent three new species and a new combination of trematodes. We found that the new species have morphological differences with their congeneric species, and we complement this information whit molecular data. Furthermore, we found morphological and molecular evidence that places Dicrocoelium rileyi within the genus Brachylecithum. This study points out the importance of comparing morphological and phylogenetic information.

A quantum leap in the evolution of platyhelminths: host-switching from turtles to hippopotamuses illustrated from a phylogenetic meta-analysis of polystomes (Monogenea, Polystomatidae)

While monogenean worms are mainly parasites of the gills and skin of fish, and to a lesser extent parasites of the oral cavity, urinary bladder, and/or conjunctival sacs of amphibians and freshwater turtles, Oculotrema hippopotami Stunkard, 1924 is the single monogenean polystome reported from a mammal, the common hippopotamus (Hippopotamus amphibius Linnaeus). Several hypotheses have been suggested in the last decade to explain the origin of this enigmatic parasite which infects the conjunctival sacs of H. amphibius. Based on a molecular phylogeny inferred from nuclear (28S and 18S) and mitochondrial (12S and COI) sequences of O. hippopotami and chelonian polystomes, we found a sister group relationship between O. hippopotami and Apaloneotrema moleri (Du Preez & Morrison, 2012). This result suggests lateral parasite transfer between freshwater turtles and hippopotamuses, thus likely reflecting one of the most exceptional known examples of host-switching in the course of vertebrate evolution. It also demonstrates that the proximity in the ecological habitat of parasites within host species is an important feature for their speciation and diversification. Because A. moleri and its host, the Florida softshell turtle (Apalone ferox (Schneider)), are restricted to the USA, we suggest that an ancestral stock of parasites may have been isolated on primitive African trionychids after they diverged from their American relatives, and then switched to hippopotamuses or anthracotheres in Africa.

No Tail No Fail: Life Cycles of the Zoogonidae (Digenea)

The Zoogonidae is the only digenean family where known cercariae lack the tail but actively search for the second intermediate host. However, the data on the zoogonid life cycles are scarce. In the present study, we elucidated and verified life cycles of the Zoogonidae from the White Sea. Using rDNA data, we showed that Pseudozoogonoides subaequiporus utilizes gastropods from the family Buccinidae as the first intermediate host and protobranch bivalves as the second one. This life cycle can be facultatively truncated: some cercariae of P. subaequiporus encyst within the daughter sporocysts. Molecular data also confirmed previous hypotheses on Zoogonoides viviapus life cycle with buccinid gastropods acting as the first intermediate hosts, and annelids and bivalves as the second intermediate hosts. We demonstrated the presence of short tail primordium in the developing cercariae of both species. Based on the reviewed and our own data, we hypothesize that the emergence of tailless cercariae in the evolution of the Zoogonidae is linked to the switch to non-arthropod second intermediate hosts, and that it possibly happened only in the subfamily Zoogoninae. Basally branching zoogonids have retained the ancestral second intermediate host and might have also retained the tail.

Trematodes of Genera Gyrabascus and Parabascus from Bats in European Russia: Morphology and Molecular Phylogeny

Morphological variability of trematodes from bats (Chiroptera) is poorly studied. Since the variability of adult digenean specimens may be rather high, morphological features are often insufficient for the identification of closely related species, and confirmation with the use of molecular data is required. The aim of our study was to combine the morphological and molecular phylogenetic analyses of several bat trematodes from the genera Gyrabascus and Parabascus (Pleurogenidae): Gyrabascus amphoraeformis, Gyrabascus oppositus, Parabascus lepidotus, Parabascus duboisi, and Parabascus semisquamosus, of which G. amphoraeformis and G. oppositus are little known in European Russia. We made detailed morphological descriptions of these trematodes from several definitive hosts, analyzed morphometric features, and generated new partial sequences of the 28S rRNA gene. A broad variability of trematodes of the genera Gyrabascus and Parabascus was revealed both from various host species and from specimens of the same host species. We propose a new taxonomic key for the identification of the studied species. Certain host specificity of these trematodes was revealed.

Invasive slipper limpets Crepidula fornicata are hosts for sterilizing digenean parasites

Invasion and spread of alien species can drive ecosystem changes, such as, the dynamics of infectious diseases. The non-native, marine gastropod Crepidula fornicata has become established across European coastlines over the last century, but there remains little insight into its disease carrying capacity and potential role as a source/sink of parasites. To address this knowledge gap, we surveyed limpets from two sites in South Wales, UK for signatures of disease/pathology using polymerase chain reaction-based methods (haemolymph) and histology (solid tissue). We encountered trematode-like parasites in ~1% individuals (5 out of 462). Three limpets displayed gross damage in the gonad, i.e. castration, and encysted metacercariae were found in the muscle of two other individuals. On the basis of 28S rDNA and internal transcribed spacer 2 genomic targets, we identified the gonad-infecting trematodes as members of the family Microphallidae – putative novel species related to the genus Longiductotrema. Earlier reports suggest that C. fornicata is not a host for trematode parasites in either its native or alien range but may act as a sink due to its filter feeding lifestyle. We provide clear evidence that C. fornicata is parasitized by at least one trematode species at two sites in Wales, UK, and likely act as a spillback or accidental host among native littorinids.

Morphological and molecular characterization of Maritrema kostadinovae n. sp. (Digenea: Microphallidae) from the yellow-crowned night heron Nyctanassa violacea (Aves: Ardeidae) in Mexico

A new species of microphallid trematode was collected from the intestine of the yellow-crowned night heron Nyctanassa violacea (L.) (Pelecaniformes: Ardeidae) from Veracruz, Mexico. Maritrema kostadinovae n. sp. differs distinctly from other members of Maritrema Nicoll, 1907 from the Americas by its smaller body size (262-435 × 242-363 μm), the extension of caeca (reaching to anterior level of ventral sucker), the size and shape of the cirrus (short, tubular and unarmed) and metraterm (simple and thin-walled), the position of the genital pore (sinistrolateral to ventral sucker) and the arrangement of the vitellaria (horseshoe-shaped with posteriorly directed opening). Maximum likelihood and Bayesian inference analyses, based on partial 28S rDNA sequences, depicted M. kostadinovae n. sp. within the genus Maritrema with strong support. The new species is in a sister position to other available members of Maritrema, except for M. subdolum Jägerskiöld, 1909 that branches as the early divergent species in the Maritrema clade. The new species is the third species of Maritrema described from birds in Mexico. Comparative morphometric data for Maritrema taxa from birds and mammals from the Americas is provided.

A new species of Atriophallophorus Deblock & Rosé, 1964 (Trematoda: Microphallidae) described from in vitro-grown adults and metacercariae from Potamopyrgus antipodarum (Gray, 1843) (Mollusca: Tateidae)

The adult and metacercaria life stages of a new species of the microphallid genus Atriophallophorus Deblock & Rosé, 1964 are described from specimens collected at Lake Alexandrina (South Island, New Zealand). In addition to molecular analyses of ribosomal and mitochondrial genes, metacercariae of Atriophallophorus winterbourni n. sp. from the snail host Potamopyrgus antipodarum (Gray) were grown in vitro to characterize internal and external morphology of adults using light and scanning electron microscopy and histological techniques. Atriophallophorus winterbourni n. sp. is readily distinguishable from Atriophallophorus coxiellae Smith, 1973 by having a different structure of the prostatic chamber, sub-circular and dorsal to genital atrium, rather than cylindrical, fibrous, elongate and placed between the seminal vesicle and the genital atrium. The new species is most similar to Atriophallophorus minutus (Price, 1934) with regards to the prostatic chamber and the morphometric data, but possesses elongate-oval testes and subtriangular ovary rather than oval and transversely oval in A. minutus. Phylogenetic analyses including sequence data for A. winterbourni n. sp. suggested a congeneric relationship of the new species to a hitherto undescribed metacercariae reported from Australia, both forming a strongly supported clade closely related to Microphallus and Levinseniella. In addition, we provide an amended diagnosis of Atriophallophorus to accommodate the new species and confirm the sinistral interruption of the outer rim of the ventral sucker caused by the protrusion of the dextral parietal atrial scale at the base of the phallus.

Five new morphological types of virgulate and microcotylous xiphidiocercariae based on morphological and molecular phylogenetic analyses

The phylogenetic position of most xiphidiocercariae from subgroups Cercariae virgulae and Cercariae microcotylae remains unknown or unclear, even at the family level. In this paper, we studied the morphology and molecular phylogeny of 15 microcotylous and virgulate cercariae (11 new and four previously described ones). Based on morphological and molecular data, we suggested five distinct morphological types of xiphidiocercariae, which are a practical alternative to Cercariae virgulae and Cercariae microcotylae subgroups. Four of these types correspond to actual digenean taxa (Microphallidae, Lecithodendriidae, Pleurogenidae and Prosthogonimidae), while the fifth is represented by Cercaria nigrospora Wergun, 1957, which we classified on the basis of molecular data for the first time. We reassessed the relative importance of morphological characters used for the classification of virgulate and microcotylous cercariae, and discussed the main evolutionary trends within xiphidiocercariae. Now stylet cercariae can be reliably placed into several sub-taxa of Microphalloidea on the basis of their morphological features.

Molecular systematics of the digenean community parasitising the cerithiid gastropod Clypeomorus batillariaeformis Habe & Kusage on the Great Barrier Reef

A rich fauna of digenetic trematodes has been documented from the Great Barrier Reef (GBR), yet little is known of the complex life-cycles of these parasites which occur in this diverse marine ecosystem. At Heron Island, a small coral cay at the southern end of the GBR, the intertidal marine gastropod Clypeomorus batillariaeformis Habe & Kusage (Cerithiidae) is especially abundant. This gastropod serves as an intermediate host for 12 trematode species utilising both fish and avian definitive hosts. However, 11 of these species have been characterised solely with morphological data. Between 2015 and 2018 we collected 4870C. batillariaeformis from Heron Island to recollect these species with the goal of using molecular data to resolve their phylogenetic placement. We found eight of the 12 previously known species and two new forms, bringing the total number of digenean species known to parasitise C. batillariaeformis to 14. The families of this trematode community now include the Atractotrematidae Yamaguti, 1939, Bivesiculidae Yamaguti, 1934, Cyathocotylidae Mühling, 1898, Hemiuridae Looss, 1899, Heterophyidae Leiper, 1909, Himasthlidae Odhner, 1910, Microphallidae Ward, 1901, and Renicolidae Dollfus, 1939. Molecular data (ITS and 28S rDNA) were generated for all trematode species, and the phylogenetic position of each species was determined. The digenean community parasitising C. batillariaeformis includes several common species, as well as multiple species which are uncommon to rare. Although most of those trematodes in the community which exploit fishes as definitive hosts have remained common, the composition of those which utilise birds appears to have shifted over time.

Microphallus ochotensis sp. nov. (Digenea, Microphallidae) and relative merits of two-host microphallid life cycles

A new digenean species, Microphallus ochotensis sp. nov., was described from the intestine of Pacific eiders (Somateria mollissima v-nigrum) from the north of the Sea of Okhotsk. It differs from other microphallids in the structure of the metraterm, which consists of two distinct parts: a sac with spicule-like structures and a short muscular duct opening into the genital atrium. Mi. ochotensis forms a monophyletic clade together with other congeneric species in phylograms derived from the 28S and ITS2 rRNA gene. Its dixenous life cycle was elucidated with the use of the same molecular markers. Encysted metacercariae infective for birds develop inside sporocysts in the first intermediate host, an intertidal mollusc Falsicingula kurilensis. The morphology of metacercariae and adults was described with an emphasis on the structure of terminal genitalia. Considering that Falsicingula occurs at the Pacific coast of North America and that the Pacific eider is capable of trans-continental flights, the distribution of Mi. ochotensis might span the Pacific coast of Alaska and Canada. The range of its final hosts may presumably include other benthos-feeding marine ducks as well as shorebirds. We suggest that a broad occurrence of two-host life cycles in microphallids is associated with parasitism in birds migrating along sea coasts. The chances that migrating birds would stop at a site where both first and second intermediate hosts occur are relatively low. The presence of a single molluscan host in the life cycle increases the probability of transmission.

Isorchis cannoni n. sp. (Digenea: Atractotrematidae) from Great Barrier Reef rabbitfishes and the molecular elucidation of its life cycle

We describe Isorchis cannoni n. sp. from the rabbitfishes Siganus fuscescens (Houttuyn) and Siganus lineatus (Valenciennes) (Siganidae) collected off Heron Island, southern Great Barrier Reef, Australia and, using molecular data, demonstrate that 'Cercariae queenslandae II' of Cannon (1978) from the gastropod Clypeomorus batillariaeformis Habe & Kosuge (Cerithiidae) is the larval form of this new species. The cercariae of I. cannoni n. sp. develop in rediae, encyst in the environment after emergence, and are inferred to then be consumed by grazing rabbitfish. Additionally, we provide a new report of Isorchis currani Andres, Pulis & Overstreet, 2016 from the type host, Selenotoca multifasciata (Richardson) (Scatophagidae) collected in Moreton Bay, south-east Queensland, Australia, greatly expanding the known geographical range of this species. Molecular sequence data (ITS1, ITS2 and 28S rDNA) generated for I. cannoni n. sp. and the new specimens of I. currani, confirm the identification of I. currani and demonstrate a distinct genotype for I. cannoni n. sp. relative to other species of Isorchis Durio & Manter, 1969, for which molecular data are available. Isorchis cannoni n. sp. is morphologically distinct from all other species in the genus, and is further distinguished by utilizing species of Siganidae as definitive hosts, rather than species of Chanidae or Scatophagidae. Because haploporid and atractotrematid cercariae have well-developed reproductive organs, we find cercariae of these closely related families morphologically distinguishable in the same way as adult trematodes: atractotrematids have two symmetrical testes and haploporids have a single testis or, rarely, two tandem or oblique testes.