Gilquiniid cestodes (Trypanorhyncha) from elasmobranch fishes off New Caledonia with descriptions of two new genera and a new species

Cestodes were collected from deep-sea sharks caught off New Caledonia, South Pacific. Vittirhynchus squali n. g., n. sp. (Trypanorhyncha: Gilquiniidae) is described from the spiral valve of Squalus melanurus Fourmanoir & Rivaton. The new genus possesses four bothria and a typical heteroacanthous metabasal armature but has a file of three macrohooks forming a short chainette on the internal surface of the basal armature. Sagittirhynchus aculeatus n. g., n. sp., from the spiral valve of Centrophorus sp. (undescribed), also has four bothria and a typical heteroacanthous armature but lacks a distinctive basal swelling and has the final hooks of each principal row prominently enlarged. Gilquinia minor n. sp., from the spiral valve of Centrophorus sp. (undescribed), is distinguished by the presence of only five hooks per principal row compared with eight in congeners. Gilquinia sp. is reported from Squalus melanurus. G. robertsoni Beveridge, 1990 is reported from S. megalops (Macleay).     

Three new genera of trypanorhynch cestodes from Australian elasmobranch fishes

Three new genera of trypanorhynch cestodes from Australian elasmobranch fishes collected in the Arafura Sea, off the Northern Territory, are described. Fossobothrium perplexum n. g., n. sp. (Otobothriidae), from the spiral valves of Anoxypristis cuspidata (Latham) and Pristis zijsron Bleeker, is similar to the otobothriid genera Pseudotobothrium Dollfus, 1942 and Poecilancistrium Dollfus, 1929 in possessing bothrial pits and a band of hooks on the tentacle, but differs from all known otobothriid genera in having the pits joined by a prominent velum. Iobothrium elegans n. g., n. sp. (Otobothriidae), from the spiral valve of Himantura jenkinsi (Annandale), is placed in the Otobothriidae because it possesses bothrial pits, but differs from Otobothrium Linton, 1890 and other genera in lacking intercalary hooks between the principal rows and in possessing a chainette on the external surface of the tentacle in the metabasal region. Oncomegoides celatus n. g., n. sp. (Eutetrarhynchidae), from the spiral valve of Dasyatis microps (Annandale) and Himantura jenkinsi, resembles Oncomegas Dollfus, 1929 in possessing two bothria and a megahook on the bothrial surface of the basal armature, but differs in possessing an extra row consisting of four intercalary hooks formed by the overlapping of two intercalary hooks on the external tentacular surface between each of the opposing principal rows and is therefore an atypical heteroacanth.     

The terminology of larval cestodes or metacestodes

The terminology associated with the nomenclature of larval or metacestodes is reviewed as well as the various morphological and developmental characters used to define different types of larval cestodes. Based on a review of the literature, the key characters differentiating the types of larval cestodes are the presence of a primary lacuna and the invagination/retraction of the scolex. The presence of a cercomer and of a bladder-like enlargement of the larval cestode were considered to be useful secondary characteristics. Using these characters, six basic types of larval cestodes were identified: the procercoid, an alacunate form which cannot develop further until ingested by a second intermediate host; the plerocercus, an alacunate form with a retracted scolex; the plerocercoid, an alacunate form with an everted scolex; the merocercoid, an alacunate form with an invaginated scolex; the cysticercoid, a lacunate form with a retracted scolex; and the cysticercus, a lacunate form with an invaginated scolex. The diversity of larval types within the broad classifications of cysticercoid and cysticercus can be differentiated by the use of appropriate prefixes. Deficiencies in knowledge of specific types of larval cestodes are identified and further avenues of research are indicated.Pseudonym for the contributors of a workshop on metacestode terminology, chaired by I. Beveridge, which took place during the Third International Workshop for Tapeworm Systematics,Sofia, Bulgaria, 20-24 July, 1999 (Organiser: B.B. Georgiev).     

Effect of mebendazole on the larval development of three Hymenolepidid cestodes.

Mebendazole or Telmin (which contains 16.7% mebendazole) markedly retarded the development of Hymenolepis diminuta and H. nana when their intermediate hosts Tribolium confusum were fed on flour mixed with it from day 1 to day 10 p.i. Though retardation also occurred with H. microstoma, the effect of the drug on this parasite was noticeably less pronounced than with the other 2 species of this genus.     

Determinants of tapeworm species richness in elasmobranch fishes: untangling environmental and phylogenetic influences

Parasite species richness is a fundamental characteristic of host species and varies substantially among host communities. Hypotheses aiming to explain observed patterns of richness are numerous, and none is universal. In this study, we use tapeworm parasites of elasmobranch fishes to examine the phylogenetic and environmental influences on the variation in species richness for this specific system. Tapeworms are the most diverse group of helminths to infect elasmobranchs. Elasmobranchs are cosmopolitan in distribution and their tapeworm parasites are remarkably host specific; therefore, making this an ideal system in which to examine global patterns in species diversity. Here, we 1) quantify the tapeworm richness in elasmobranch fishes, 2) identify the host features correlated with tapeworm richness, and 3) determine whether tapeworm richness follows a latitudinal gradient. The individual and combined effects of host size, factors associated with water temperatures (influenced by latitude and depth), host habitat, and type of elasmobranch (shark or batoid) on measures of species diversity were assessed using general linear models. These analyses included tapeworm host records for 317 different elasmobranch species (124 species were included in our analyses) and were conducted with and without taking into account phylogenetic relationships between host species. Since sharks and batoids differ substantially in body form, analyses were repeated for each host subset. On average, batoids harboured significantly more tapeworm species than shark hosts. Tapeworm richness in sharks was influenced by median depth, whereas no predictor variable included in our models could adequately account for interspecific variation in tapeworm richness in batoid hosts. The taxonomic diversity of tapeworm assemblages of sharks and batoids was influenced by median depth and median latitude, respectively. When the influence of host phylogeny is accounted for, larger hosts harbour a greater tapeworm richness, whereas hosts exploiting wider latitudinal ranges harbour more taxonomically distinct tapeworm assemblages. Species richness and taxonomic diversity of tapeworm assemblages in elasmobranch fishes are influenced by different evolutionary pressures, including host phylogenetic relationships, space constraints and geographical area. Our results suggest that ca 3600 tapeworm species have yet to be described from elasmobranch fishes.     

Fine structure of glial cells in the central nervous system of the tapeworm Grillotia erinaceus (Cestoda: Trypanorhyncha)

The problem of glial cells existing in parasitic and free living flatworms is correlated with organization of parenchyma in platyhelmintes. In the contrary to the widespread opinion that myelin-like envelopes and glial cells do not exist in the nervous system of parasitic flatworms, it has been shown by ultrastructural researches that Amphilina foliacea (Cestoda, Amphilinidea) has well developed glial cells and myelin-like envelopes in the ganglia and main cords, which include both glial cells and intercellular components. The aim of our research was to reveal and investigate in details structural components corresponding to the concept of the glial cell in the CNS of Grillotia erinaceus (Cestoda: Trypanorhyncha). Three types of glial cells have been found. The first type is the fibroblast-like glial cells; cells locate in the cerebral ganglion, contain in cytoplasm and extract out fibrillar matrix, form desmosomes and have supporting function. The glial cells of the second type form myeline-like envelope of the giant axons and bulbar nerves in scolex and have laminar cytoplasm. These cells are numerous and exceed in number the neurons bodies into the nerve. The glial cells of the third type form multilayer envelopes in the main nerve cords; extra cellular fibers and gap-junctions take place between the layers. There are contacts between the glial cells of the third type and excretory epithelium but specialized contacts with neurons have been not found. The existing of glial cells in free living and parasitic flatworms is discussed.     

Polycystic echinococcosis in Colombia: the larval cestodes in infected rodents.

Described are the characteristics of the polycystic larval cestodes found in an endemic area of echinococcosis in the Easter Plains of Colombia and the tissue reaction evoked in infected rodents. Of 848 free-ranging animals examined, polycystic hydatids were found in 44/93 Cuniculus paca and 1/369 Proechimys sp. None of 20 Dasyprocta fuliginosa examined was infected, but hunters provided a heart with hydatid cysts and information about two additional animals with infected livers. Recognition of an endemic area of polycystic echinococcosis provides a means to investigate the life cycle of the parasites and to study the histogenesis of the larval cestodes in susceptible laboratory animals.     

Preliminary cladistic analysis of genera of the cestode order Trypanorhyncha Diesing, 1863

A preliminary cladistic analysis was carried out on the 49 currently recognised genera of the order Trypanorhyncha. Forty-four characters were analysed; a functional outgroup was used for scolex and strobilar characters, while Nybelinia was utilised to polarise characters related to the rhyncheal system. Eight well-resolved clades were evident in the resultant cladogram, which is compared with existing phenetic classifications. An analysis of families resulted in a similar clustering of taxa to that observed in the case of the genera. The results suggest that two key characters used in existing classifications, namely the presence of sensory fossettes on the bothridia and the development of atypical heteroacanth and poeciloacanth armatures from typical heteroacanth armatures, have occurred on several occasions. Some clades provide support for the arrangements used in current classifications. Suggestions are made for future avenues of research which might provide more robust phylogenetic data for the Trypanorhyncha.     

Similarity and specialization of the larval versus adult diet of European butterflies and moths

Many herbivorous insects feed on plant tissues as larvae but use other resources as adults. Adult nectar feeding is an important component of the diet of many adult herbivores, but few studies have compared adult and larval feeding for broad groups of insects. We compiled a data set of larval host use and adult nectar sources for 995 butterfly and moth species (Lepidoptera) in central Europe. Using a phylogenetic generalized least squares approach, we found that those Lepidoptera that fed on a wide range of plant species as larvae were also nectar feeding on a wide range of plant species as adults. Lepidoptera that lack functional mouthparts as adults used more plant species as larval hosts, on average, than did Lepidoptera with adult mouthparts. We found that 54% of Lepidoptera include their larval host as a nectar source. By creating null models that described the similarity between larval and adult nectar sources, we furthermore showed that Lepidoptera nectar feed on their larval host more than would be expected if they fed at random on available nectar sources. Despite nutritional differences between plant tissue and nectar, we show that there are similarities between adult and larval feeding in Lepidoptera. This suggests that either behavioral or digestive constraints are retained throughout the life cycle of holometabolous herbivores, which affects host breadth and identity.     

Host specificity of homoxenous trypanosomatids

Some problems in a correct using of the term "host specificity" for parasitic protozoans and specifically for the trypanosomatids are discussed. Results of investigation the host specificity of the trypanosomatids obtained by traditional methods are summarized. Host specificity data of some insect-associated trypanosomatids based on the identification of parasites by means of molecular methods is discussed. The subjectivity is an imminent distinctive feature of host specificity investigation in parasitic protozoans--trypanosomatids, especially in parasites of insects and plants. There is a vicious circle, when the conclusions about specificity are related with the necessity of taxonomic identification of the parasites during the process of biodiversity and ecological studies. The taxonomic position of parasite is often determined based on a data of observed hosts specificity. This is quite common in cases, when reliable morphological characters are absent, and it indeed takes place in the homoxenous trypanosomatids. The using of molecular markers only allows to reliably identify and compare the parasites, without involving the properly taxonomic data, and finally to make more objective conclusions about their host specificity. A crucial question in this kind of investigation is an obtaining of adequate and wide set of laboratory cultures (isolates) correctly reflecting the diversity of the hosts. It is always necessary to take in attention a possibility of occasional infections, which could misrepresent obtained results. About 50 cultures isolated from different hosts (mostly Hemiptera: Heteroptera) and places (mostly North Russia) have been examined by means of RAPD, UP-PCR, MLEE and cross DNA hybridization. Some of them were placed in rRNA-based molecular phylogeny. As it was found out, none natural groups of homoxenous trypanosomatids (groups of similar genomes) demonstrated a clear preferential distribution on certain insect taxon of any taxonomic rank,--species, genera, family and even order. It is postulated that the host specificity of insect-associated trypanosomatids is extremely wide.     

The source of antigen in an adult tapeworm

Hopkins C. A. and Barr I. F. 1982. The source of antigen in an adult tapeworm. International Journal for Parasitology12: 327–333. Although a primary infection of Hymenolepis diminuta is not rejected for 9–15 days by a mouse, it has been shown that a primary infection terminated chemically after only 3 days induces as good protection against challenge. This demonstrated that a scolex and 1–2 mm of neck tissue (all that is formed by day 3 post infection) are an adequate source of ‘protective’ antigen. Irradiated (350 Gy) cysticercoids which survive but show little growth immunize as effectively as normal cysticercoids which indicates actively growing neck tissue is not essential and hence the scolex alone is a sufficient source of ‘protective’ antigens. In the rat irradiated cysticercoids were found to establish, double their length over 3–6 days and then slowly shrink, but 14% of the worms were still present 49 days p.i. Although a primary infection of normal worms in a rat markedly depresses growth of a secondary infection administered 7 days after the chemical expulsion of the primary, irradiated scoleces induced no measurable protection. These results are discussed in relation to the source of antigen and the fundamental difference in the protective response of mice (an abnormal host) and rats (a normal host) to the tapeworm H. diminuta in the small intestine.     

The fine structure of frontal glands in adult cestodes

Kuperman B. I. & Davydov V. G. 1982. The fine structure of frontal glands in adult cestodes. International Journal for Parasitology12: 285–293. The localization and structure of frontal glands of adult cestodes of 20 species from 4 orders: Caryophyllidea, Pseudophyllidea, Proteocephalidea and Cyclophyllidea were studied by light and electron microscopy. In cestodes of various orders there was evidence of differences in the ultrastructure of secretory cells, in the character of the secretion, and in the method of its discharge. The localization of glands in most adult cestodes is in the scolex. In Cyatocephalus, Ligulidae, Bothriocephalus claviceps, they are distributed also in the anterior and middle part of the body. In the species Caryophylleus (C. laticeps) and Khawia sinensis a major gland complex previously not described was discovered. The glands of the cestodes investigated may be divided into three main groups by their structure, localization and functional role in ontogenesis: (1) penetration glands in oncospheres which develop into procercoids and plerocercoids; (2) glands of plerocercoids and adult cestodes which develop in the gut; (3) gland complexes in the representatives of the order Caryophyllidea. The secretion is usually discharged at the scolex region and less frequently on the lateral surface. Three different ways of discharging secretory material from the cestodes body are described.     

Parental effects on the larval performance of a tapeworm in its copepod first host

Parents can influence the phenotype of their offspring through various mechanisms, besides the direct effect of heredity. Such parental effects are little explored in parasitic organisms, perhaps because in many parasites, per capita investment into offspring is low. I investigated whether parental identity, beyond direct genetic effects, could explain variation in the performance of the tapeworm Schistocephalus solidus in its first intermediate host, a copepod. I first determined that two breeding worms could be separated from one another after ~48 h of in vitro incubation and that the isolated worms continued producing outcrossed eggs, that is, rates self‐fertilization did not increase after separation. Thus, from a breeding pair, two sets of genetically comparable eggs can be collected that have unambiguous parental identities. In an infection experiment, I found that the development of larval worms tended to vary between the two parental worms within breeding pairs, but infection success and growth rate in copepods did not. Accounting for this parental effect decreased the estimated heritability for development by nearly half. These results suggest that larval performance is not simply a function of a worm's genotype; who mothered or fathered an offspring can also affect offspring fitness, contradicting the perhaps naïve idea that parasites simply produce large quantities of uniformly low‐quality offspring.