Egg capsule dimensions as a taxonomic criterion in the digenean family transversotrematidae

Egg capsule morphometrics of the ectoparasitic digenean Transversotrema patialense are examined. Capsule width, but not length, shows age-dependency over the ovigerous life span of the fluke at 24°C. Capsule length is normally distributed. A comparison between 7 species of the family Transverso-trematidae indicates that the published data on egg dimensions are inadequate for statistical analyses. Simple methods for strengthening the role of egg capsule dimensions in numerical taxonomy are suggested.     

The ultrastructure of the spermatozoon of Neochasmus sp. (Cryptogonimidae, Digenea, Trematoda) and its phylogenetic significance

Jamieson B. G. M. and Daddow L. M. 1979. The ultrastructure of the spermatozoon of Neochasmus sp. (Cryptogonimidae, Digenea, Trematoda) and its phylogenetic significance. International Journal for Parasitology12: 547–559. The typical spermatozoon is filiform, monopartite and internally strongly asymmetrical, with a mean length of 254 μm. Its two axonemes are wholly incorporated though not deeply. The six major regions, in anteroposterior (proximal-distal) sequence, are: acrosomoid, prenuclear, uniaxonemal, nuclear, intermediate (amitochondrial), posterior mitochondrial and posterior amitochondrial regions. Centrioles and flagellar rootlets, present in the spermatid, are absent from the spermatozoon. The right axoneme (axial unit) originates more anteriorly than the left and anteriorly bears an acrosome-like projection (acrosomoid). Spinose regions carrying epiplasmalemmal projections are reported for the first time in the Digenea. Dimorphism exists as replacement of the typical posterior mitochondrial and amitochondrial regions by an amitochondrial region characterized by asymmetrical distribution of spines around one axoneme. Excepting known schistosomatid sperm, the digenean sperm is diagnosed by the combination of three characters: cortical microtubules, two fully incorporated 9 + 1 axonemes and presence of mitochondria although no one of these characters is limited to the group. Subtle intertaxon variations occur.     

The ultrastructure of the spermatozoon and spermiogenesis in Cryptocotyle lingua (digenea: Heterophyidae)

During spermiogenesis two lateral flagellar processes and a median process arising from the apex of the zone of differentiation, fuse to form the elongated unipartite spermatozoon. Two axial units, therefore, with the ‘9+1’ pattern of microtubules are incorporated into the spermatozoon. The nucleus, in the head region, contains dense lamellar subunits arranged in a spiral in the long axis. These are formed by condensation of the chromatin during spermiogenesis. The single elongated mitochondrion, resulting from early fusion of small mitochondria, extends through the head and middle regions of the spermatozoon. Peripheral microtubules, present originally in the zone of differentiation, are arranged in straight dorsal and ventral rows, along the length. β glycogen particles accumulate in the spermatozoa after they have separated from the residual cytoplasm. Spermatozoa are present in the testes on the second day after infection of the bird host and accumulate in the vesicula seminalis from the third day onwards.     

Ultrastructural observations on the sensory papillae of juvenile and adult Gorgoderina vitelliloba (Trematoda: Gorgoderidae)

Hoole D. and Mitchell J.B. 1981. Ultrastructural observations on the sensory papillae of juvenile and adult Gorgoderina vitelliloba (Trematoda : Gorgoderidae). International Journal for Parasitology11: 411–417. Ultrastructural observations have been made on the juvenile and adult stages of Gorgoderina vitelliloba from Rana temporaria. Four types of sensory papillae occur; button, rosette, ciliated and domed. Button papillae, which contain a ciliary-rootlet but lack a cilium, occur on the oral sucker, dorsal preacetabular surface and the lateral margins of the fluke. Scanning electron microscopical observations reveal that the tegumental protuberances of the papilla are transformed from a spiked or conical appearance in juvenile flukes to a rounded form in adult flukes. Rosette papillae, which also contain a rootlet, occur on the lip of the ventral sucker of both juvenile and adult flukes. Ciliated papillae only occur on the oral sucker of juvenile flukes. Domed papillae, which contain a large area of electron-dense material, occur on the internal surface of the ventral sucker of both juvenile and adult flukes. The functions of papillae and their possible role in the migration of the parasite are discussed.     

Tegumental ultrastructure of adult Gynaecotyla squatarolae (Digenea: Microphallidae)

Gynaecotyla squatarolae (Digenea: Microphallidae) adult flukes were recovered from experimental chicks at day 4-6 post-infection and their tegumental ultrastructure was observed with a scanning electron microscopy. They were pyriform in shape, and their anterior halves were concaved ventrally. The whole body surface was covered with tegumental spines, which were wide and 16-17 digitated between oral and ventral suckers. The density of spines and number of digits decreased posteriorly. The oral sucker was subterminal and the excretory pore was at the posterior end of the worm. Two ventral suckers were similar in appearance and protruded near midline of the worm. The genital atrium was dextral to the small ventral sucker. The dorsal surface was covered with tegumental spines, but the spines were sparser than on the ventral surface. On the middle portion of the dorsal surface, a small opening presumed to be the Laurer's canal was seen. From these findings, it has been confirmed that the adult G. squatarolae has unique characteristics in the surface ultrastructure.     

Age- and density-dependent growth within populations of the ectoparasitic digenean Transversotrema patialense on the fish host

Mills C. A. 1980. Age- and density-dependent growth within populations of the ectoparasitic digenean Transversotrema patialense on the fish host. Internationaljournal for Parasitology, 10: 287–291. Growth of the adult ectoparasitic digenean Transversotrema patialense on the fish host Brachydanio rerio is shown to be age-dependent, ceasing 15–20 days post infection. The vitelline glands expand greatly in size after infection from 1.25 % of cercarial area to 20.7 % of that of the mature adult. There is an increase in the occurrence of reproductive abnormalities in old parasites but this alone fails to account for the decline in egg production found as populations of T. patialense age. Growth of adult T. patialense is density-dependent with reduced growth at high initial parasite densities per host.     

Phylogeny and classification of the Digenea (Platyhelminthes: Trematoda)

Complete small subunit ribosomal RNA gene (ssrDNA) and partial (D1-D3) large subunit ribosomal RNA gene (lsrDNA) sequences were used to estimate the phylogeny of the Digenea via maximum parsimony and Bayesian inference. Here we contribute 80 new ssrDNA and 124 new lsrDNA sequences. Fully complementary data sets of the two genes were assembled from newly generated and previously published sequences and comprised 163 digenean taxa representing 77 nominal families and seven aspidogastrean outgroup taxa representing three families. Analyses were conducted on the genes independently as well as combined and separate analyses including only the higher plagiorchiidan taxa were performed using a reduced-taxon alignment including additional characters that could not be otherwise unambiguously aligned. The combined data analyses yielded the most strongly supported results and differences between the two methods of analysis were primarily in their degree of resolution. The Bayesian analysis including all taxa and characters, and incorporating a model of nucleotide substitution (general-time-reversible with among-site rate heterogeneity), was considered the best estimate of the phylogeny and was used to evaluate their classification and evolution. In broad terms, the Digenea forms a dichotomy that is split between a lineage leading to the Brachylaimoidea, Diplostomoidea and Schistosomatoidea (collectively the Diplostomida nomen novum (nom. nov.)) and the remainder of the Digenea (the Plagiorchiida), in which the Bivesiculata nom. nov. and Transversotremata nom. nov. form the two most basal lineages, followed by the Hemiurata. The remainder of the Plagiorchiida forms a large number of independent lineages leading to the crown clade Xiphidiata nom. nov. that comprises the Allocreadioidea, Gorgoderoidea, Microphalloidea and Plagiorchioidea, which are united by the presence of a penetrating stylet in their cercariae. Although a majority of families and to a lesser degree, superfamilies are supported as currently defined, the traditional divisions of the Echinostomida, Plagiorchiida and Strigeida were found to comprise non-natural assemblages. Therefore, the membership of established higher taxa are emended, new taxa erected and a revised, phylogenetically based classification proposed and discussed in light of ontogeny, morphology and taxonomic history.     

Cercaria caribbea LVIII Cable, 1963 (Digenea: Cyathocotylidae) in the Republic of Korea and its surface ultrastructure

Cercaria caribbea LVIII Cable, 1963 (Digenea: Cyathocotylidae) was detected from a brackish water gastropod species (Cerithideopsilla cingulata) in a coatal area of Shinan-gun, Jeollanam-do (Province), the Republic of Korea, and its surface ultrastructure was studied using a scanning electron microscope. The cercariae were found freely swimming or enveloped within daughter sporocysts when the snail host was mechanically broken. They were morphologically characterized by a linguiform and ventrally concave body, a long and bifurcated tail, and the presence of a holdfast (=tribocytic) organ posterior to the ventral sucker. On the whole ventral and dorsal surfaces, peg-like tegumental spines were densely distributed. Around the oral sucker, several sensory papillae, each with a short cilium, were distributed, and on the tail, sensory papillae, each with an extensively long cilium, were observed. This is the first record describing a cyathocotylid cercaria from a brackish water gastropod in the Republic of Korea.     

Ultrastructure of the foregut and associated glands in the lung fluke,Paragonimus miyazakii (Digenea: Troglotrematidae), with particular reference to their functional roles

The foregut and associated glands of a digenetic trematode, Paragonimus miyazakii, were examined in the forebody by transmission and scanning electron microscopy as well as by light microscopy, and their functional roles were discussed. The foregut is lined with a general tegument without spines and sensory receptors throughout its length, although it consists of the mouth, pharynx, and esophagus. This foregut tegument is regionally and intraregionally modified in appearance, suggesting the performance of auxiliary functions in digestion. This appearance is characterized by long, frequent cytoplasmic extensions of the apical tegument around the middle portion of the mouth and the anterior esophagus. Electron-dense granules and multimembranous and multilamellar bodies are developed in the tegument to various degrees, and elaborately in the apical layer of the prepharynx. A single type of unicellular gland is embedded in the antero-middle part of the worm in small groups. The gland cells synthesize clear secretory granules as a chief product, each granule with a pleomorphic, dense, core-like inclusion. Mature granules are elliptical in shape, approximately 500 nm in diameter, and are subsequently discharged into the prepharyngeal foregut lumen after passing through the elongated cytoplasm of the gland cell. In the prepharynx and pharynx, host blood cells are apparently processed for digestion. In the wide lumen of the esophagus, foodstuff could undergo sufficient digestion prior to absorption by the cecal epithelium. J. Morphol. 237:43–52, 1998. © 1998 Wiley-Liss, Inc.     

Redescription and surface ultrastructure of Pygidiopsis macrostomum (Digenea: Heterophyidae)

Pygidiopsis macrostomum Travassos, 1928, a poorly known species originally described from a single specimen from Rattus norvegicus (Erxleben, 1777) in Brazil, is redescribed on the basis of metacercariae from the mesenteries of naturally infected guppies Poecilia vivipara Bloch and Schneider, 1801 (Poeciliidae), and adults obtained from an experimental infection of hamsters. Pygidiopsis macrostomum is characterized by the absence of oral spines, vitellaria extending forward to ventral sucker, uterus reaching pharyngeal level, X-shaped excretory vesicle, and an oral sucker/acetabulum ratio of 1:0.8. The surface ultrastructure shows that the tegument of the metacercaria does not strongly differ from that of adults. The brush-shaped spines of P. macrostomum are similar to those reported for Pygidiopsis summa and Pygidiopsis ardeae, but no differences in spine shape were observed throughout the body.     

Sperm characters of the digenean Nephrotrema truncatum (Troglotrematidae): a kidney parasite of Crocidura russula (Soricidae) and their phylogenetic significance

ABSTRACT

Spermatological characteristics of the troglotrematid digenean Nephrotrema truncatum, a parasite of the shrew Crocidura russula, have been investigated by means of transmission electron microscopy. The ultrastructural study reveals that the mature spermatozoon of N. truncatum exhibits many ultrastructural characters previously described in most gorgoderoideans. These are two axonemes of the 9+‘1‘ trepaxonematan pattern, four attachment zones, a lateral expansion, an external ornamentation of the plasma membrane associated with spine-like bodies and cortical microtubules, and in the posterior part of the anterior spermatozoon region, two bundles of parallel cortical microtubules with the maximum number located in the anterior part of the spermatozoon, a nucleus, two mitochondria, and granules of glycogen. The obtained results are compared with those of other digeneans, particularly the Gorgoderoidea. The sperm cells gorgoderoideans are of type IV, characterised by a 9+‘1‘ pattern of axonemes, the presence of an external ornamentation associated with cortical microtubules and located in the posterior area of the anterior extremity, the presence of two bundles of cortical microtubules, the maximum number of cortical microtubules located in the anterior region of the spermatozoon, and the presence of generally two mitochondria. However, dicrocoeliids and troglotrematids have spermatozoa with ornamentation of the plasma membrane and lateral expansions.     

Tegumental ultrastructure of the juvenile and adult Himasthla alincia (Digenea: Echinostomatidae)

The tegumental ultrastructure of juvenile and adult Himasthla alincia (Digenea: Echinostomatidae) was observed by scanning electron microscopy. One-, 5- (juveniles) and 20-day-old worms (adults) were harvested from chicks experimentally fed metacercariae from a bivalve, Mactra veneriformis. The juvenile worms were elongated and curved ventrally. The head crown bore 31 collar spines, arranged in a single row. The lip of the oral sucker had 12 paired, and 3 single type I sensory papillae, and the ventral sucker had about 25 type II sensory papillae. The anterolateral surface between the two suckers was densely packed with tegumental spines with 4-7 pointed tips. The adult worms were more elongated and filamentous, and had severe transverse folds over the whole body surface. On the head crown and two suckers, type I and II sensory papillae were more densely distributed than in the juvenile worms. Retractile brush-like spines, with 8-10 digits, were seen on the anterolateral surface, whereas claw-shaped spines, with 2-5 digits, were sparsely distributed posteriorly to the ventral sucker. The cirrus characteristically protruded out, and was armed with small spines distally. The surface ultrastructure of H. alincia was shown to be unique among echinostomes, especially in the digitation of its tegumental spines, the distribution of sensory papillae and by severe folds of the tegument.     

A new species of Proctoeces and reinstatement of Proctoeces humboldti George-Nascimento and Quiroga 1983 (Digenea: Fellodistomidae) based on molecular and morphological evidence

The most studied digenean of marine organisms in Chile is by far Proctoeces humboldti, a parasite of the intestine of the clingfish Sicyases sanguineus and gonad of the keyhole limpet Fissurella spp. (progenetic metacercariae). The mussel Perumytilus purpuratus has been suggested as the first intermediate host for this digenean. In a study examining the parasites of S. sanguineus from central Chile, we found specimens of Proctoeces showing significant morphological differences with P. humboldti. To assist in the resolution of the taxonomic identification of these specimens, as well sporocysts obtained from the mussel P. purpuratus from central and northern Chile, phylogenetic studies using DNA sequences from the SSU rRNA, as well the LSU rRNA and Cox 1 gene were performed. Results showed that the clingfish S. sanguineus is a host for two species of Proctoeces (P. humboldti and P. syciases n. sp.) along the northern and central Chilean coast, without geographic separation; the mussel P. purpuratus is the first intermediate host for P. syciases n. sp. but not for P. humboldti in central and northern Chile. Fissurellids (Archaeogastropoda) along the Chilean coast harbor only progenetic stages of P. humboldti, but there is no evidence of progenesis for P. syciases. The reinstatement of Proctoeces humboldti is strongly suggested.     

Ultrastructure of the spermatozoon of Centroderma spinosissima (Stossich, 1886) (Digenea: Mesometridae) and its phylogenetic potential

The Mesometridae includes only five genera and eight species. The available data on the ultrastructure of sperm cells of mesometrid species referred to two species only, Elstia stossichianum and Wardula capitellata. The present study revealed the ultrastructure of the spermatozoon of a third genus and third species of Mesometridae, Centroderma spinosissima. The mature spermatozoon of C. spinosissima presents two axonemes with different lengths of the Ehlers’ 9 + ‘1’ trepaxonematan pattern, a nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, a lateral expansion, spine-like bodies, cytoplasmic ornamented buttons and granules of glycogen. The spermatozoon of C. spinosissima is similar to those of the previously studied mesometrids. However, some peculiarities such as the presence of two mitochondria, the disposition of the external ornamentation of the plasma membrane and the morphology of the posterior spermatozoon extremity, characterize the male gamete of C. spinosissima. Moreover, the presence of cytoplasmic ornamented buttons is a characteristic found only in the mature spermatozoon of mesometrids and it probably represents an autapomorphy for this family.     

Biosteres longicaudatus: Developmental dependence on host (Anastrepha suspensa) physiology

Larvae of Anastrepha suspensa that were in the first day of the third instar were parasitized by females of the solitary endoparasitoid, Biosteres longicaudatus. At the end of the 6-hr oviposition period, larvae were ligated posterior to the ring gland so that some larvae had parasitoids anterior to the ligature while in others, the parasitoids were in the abdomen, posterior to the ligature. Ninety-two percent of the parasitoids anterior to the ligature hatched to the first through third instars. Parasitoids posterior to the ligature had a 75% egg hatch to the first instar only. No larval molts to the second or subsequent instars occurred in these parasitoids. Upon parabiosis to 3-day-old, unparasitized host pupae, the ligated larvae pupated and 97% of the first-instar parasitoids in these parabiosed larval abdomens molted to the second instar. Newly laid parasitoid eggs transplanted to 3-day-old pupal hosts had less than one-third of the egg hatch of those transplanted to first-day third-instar hosts. The data implicate the physiological state of the host (vis-a-vis pupation and associated events) as being an important factor in the development of the endoparasitoid.     

The surface topography and ultrastructure of the tegument and haptor of Pricea multae (Monogenea)

Full-size image

and 1986. The surface topography and ultrastructure of the tegument and haptor of Pricea multae (Monogenea). International Journal for Parasitology 16: 581–589. Pricea multae is a gill parasite of Scomberomorus spp. In the present study, the surface specialization and ultrastructure of the tegument and haptor were examined in detail. The buccal cavity and the preoral pit bear uniciliated sensory endings. The genital atrium opens on the ventral surface whereas the vaginal pore opens on the dorsal surface of the anterior region. The general body surface is elevated by pits and folds together with papillae-like uniciliated sensory endings. Microvilli are uncommon.

The syncytium of the tegument is bounded by apical and basal plasma membranes. Some electron-dense granules and electron-lucent vesicles were observed exocytosing at the apical surface. The tegumental perikarya lie amongst the muscle blocks underneath the basal lamina. The body wall muscle fibres are non-striated consisting of thick and thin myofilaments. Each muscle fibre is limited by a sarcolemma and separated from neighbouring fibres by interstitial material.

The haptor possesses two rows of pincer-type clamps. The clamps may be withdrawn by muscles into cavity-like depressions. Electron-dense fibrils are embedded within the clamp sclerite matrix. The intrinsic muscles of the clamp include radial muscles enclosed within the basal lamina. The muscle fibres enclosed within the basal lamina of the clamp appear to differ from the body wall muscles by the absence of interstitial material, the possession of well defined gap junctions between the sarcolemma of adjacent muscle fibres, abundant sarcoplasmic reticulum and numerous mitochondria. The extrinsic muscles of the clamp presumably arise from the dorso-lateral surface of the haptor and are apparently connected to the tendon of the clamp. A cluster of gland cells occurs in the haptor beneath each clamp. The haptor is richly supplied with nerve fibres which are associated with groups of neurones. Each axon is non-myelinated and contains presumed neurosecretory granules. The peripheries of some of the large axons are subdivided by invaginations of the axon wall.     

Two new blood flukes (Digenea: Sanguinicolidae) from Epinephelinae (Perciformes: Serranidae) of the Pacific Ocean

Pearsonellum pygmaeus n. sp. is described from Cromileptes altivelis (Serranidae), the Barramundi Cod, from Heron Island (southern Great Barrier Reef) and Lizard Island (northern Great Barrier Reef). This new species differs from Pearsonellum corventum (type and only species) in the combination of smaller overall body size, the relative distance of the brain from the anterior end, the relative lengths of both the oesophagus and the testis, the degree to which the testis extends outside the intercaecal field, the shape of the testis, the shape and size of the ovary and the extent to which the uterus loops around the ovary. There are in addition, 20 base pair differences between the ITS2 rDNA sequence of P. pygmaeus n. sp. and that of P. corventum. Three new host records for P. corventum are reported. Adelomyllos teenae n. g., n. sp. is described from Epinephelus coioides (Serranidae), the Estuary Cod, from Moreton Bay, southeast Queensland. The new genus differs from the 22 other sanguinicolid genera in the combined possession of two testes, a cirrus-sac, separate genital pores, a post-ovarian uterus and an H-shaped intestine. A. teenae n. sp. is the third sanguinicolid described from the Epinephelinae. Sanguinicolids have now been reported from 11 species of Serranidae.     

Interrelationships of the Haploporinae (Digenea: Haploporidae): A molecular test of the taxonomic framework based on morphology

The taxonomic framework of the Haploporidae is evaluated and the relationships within the Haploporinae are assessed for the first time at the generic level using molecular data. Partial 28S and complete ITS2 rDNA sequences from representatives of six of the nine recognised genera within the Haploporinae were analysed together with published sequences representing members of two haploporid subfamilies and of the closely related family Atractotrematidae. Molecular analyses revealed: (i) a close relationship between the Atractotrematidae and the Haploporidae; (ii) strong support for the monophyly of the Haploporinae, Dicrogaster and Saccocoelium, and the position of Ragaia within the Haploporinae; (iii) evidence for rejection of the synonymy of Saccocoelioides and Lecithobotrys and the validity of the Dicrogasterinae; and (iv) support for the distinct status of Saccocoelium in relation to Haploporus. The wider sampling within the genera Dicrogaster and Saccocoelium confirmed the distinct status of the included species, thus rejecting previously suggested synonymies. Saccocoelioides, recently transferred to the Chalcinotrematinae, was nested within the Haploporinae and this was largely associated with the position of Forticulcita, resolved as the most basal haploporine genus. Forticulcita also possesses a well-delimited eversible intromittent copulatory organ, a feature unique in the Haploporidae which has not been previously considered an important apomorphy. This, in association with the present hypothesis of the Haploporinae based on molecular data, led us to erect Forticulcitinae subf. n. for Forticulcita; this resolved Saccocoelioides and, by extension the Chalcinotrematinae, as sister groups to the Haploporinae.     

Deterioration patterns in diapausing egg banks of Brachionus (Müller, 1786) rotifer species

Rotifers are cyclical parthenogens that produce sexual diapausing eggs at some stage in their life cycle. These eggs are encysted embryos that remain viable for extended periods in lake and pond sediments, thus acting as an egg bank with many ecological and evolutionary consequences. Despite its importance to rotifer evolution, there are no studies on resting egg deterioration and associated processes in natural environments. In this study, more than 4000 diapausing eggs of species from the Brachionus plicatilis complex, which includes several closely related cryptic species, were collected from different sediment depths in 15 ponds in eastern Spain and were classified according to three features thought to be related to their viability: shell integrity, embryo size, and embryo colour. A positive association was found between embryo size and hatching success in those eggs having an intact shell. Diapausing eggs that showed good shell integrity and no more than a 25% reduction of multinuclear embryo maximum size were classified as healthy and 98.9% hatched. Darkening of diapausing egg embryo was an indicator of viability loss. A decreasing frequency of healthy-looking diapausing eggs was observed with increasing sediment depth, although some exceptions were found.