Parasites may affect host demographic characteristics because they can directly or indirectly cause the death of their hosts and/or influence their reproduction. Parasitism is therefore recognized as a factor that influences the composition and structure of populations and communities. One of these behaviours is the compensatory response: the host can compensate for the parasite losses effect, modifying the reproductive effort to enhance fitness. Ovigerus female Palaemonetes argentinus was collected and sorted into two groups according to the degree of development of their embryos: newly spawned embryos and embryos ready to hatch. The number of embryos and their dry weight for each female were determined. All parts of the female body were checked for parasites. The females of P. argentinus were parasitized by Microphalus szidati. We found that parasitized females produce more embryos but had more egg loss during development and the percentage of embryonic loss was higher in the parasitized females than in non-parasitized. Parasitized females produced lighter eggs than those from uninfected females. This supports the compensatory reproduction hypothesis suggested for this species. Parasitism can change life history traits in a way that fecundity can be compensated; this co-evolution between host and parasites will be population or context dependent. Parasites are a functional part of any ecosystem and as our results show, deleting parasites in life history traits and reproduction studies in free living organisms could lead to an incomplete picture of the true processes that happen in nature.

In Britain, the year 1937 is likely to be memorable in the history of cultivation of many species and varieties of plants belonging to the genus Primula, as witnessing, for the first time, attacks of great severity by the nematode, Anguillulina dipsaci in a number of plantations of Primulas, reducing the vitality of the plants wherever it occurred, and in many instances causing complete destruction of certain species. The plants classed as members of the Candelabra Section, which includes some of the finest and most extensively grown species and varieties in the whole genus, proved particularly susceptible but, while members of many of the other Sections of Primulas did not escape attack, the injury inflicted was not usually of such high order of severity.

Previously, an in vitro effect was observed on the complement system not only of the excretory-secretory products but also of somatic antigens from L3 Anisakis simplex larvae. In the present work the effect of anti-A. simplex specific antibodies on C3 and C4 levels in human sera was investigated. Up to 309 samples of sera were tested to determine levels of C3 and C4 and anti-A. simplex antibodies, including immunoglobulins IgG, IgM, IgA and IgE. Significant differences were observed between levels of C3 and C4 and all immunoglobulins except for IgE. In the case of immunoglobulins, the probability that an anti-A. simplex positive subject has a C3 deficiency was 3.8 times higher than a subject without specific antibodies. In conclusion, an association between elevated levels of anti-A. simplex antibodies and C3 and C4 deficiency was demonstrated.

All Pseudocorynosoma species inhabit freshwater environments of the American continent, but little is known about their life cycles. We report Pseudocorynosoma enrietti (Molfi & Freitas Fernandes, 1953) from natural and experimental specimens in Patagonia and identify the intermediate and definitive hosts of its life cycle for the first time in South America. Adult worms were recovered from Anas platyrhynchos (Linnaeus) and from a new definitive host, Coscoroba coscoroba Molina. Naturally infected amphipods, Hyalella patagonica Ortmann, were collected to obtain cystacanths that were fed to Gallus gallus domesticus (Linnaeus) and Anas platyrhynchos. Specimens of P. enrietti are described in detail using light and scanning electron microscopy. A key to species of the genus Pseudocorynosoma is included. Worms are characterized in both sexes by fore-trunk spines, and genital spines in an isolated field. The proboscis has 19–20 hook rows; males have 9–11 (10) hooks per row and females 7–9 (8). Males with four cement glands similar in size. Eggs elongated, with filaments. Experimental male and female worms were recovered from A. platyrhynchos at seven and 14 days, post-infection.

Digenean larvae of hermaphroditic generation – cercariae – are known to be polymorphic at genetic and behavioural levels. Cercariae arise as a result of parthenogenetic reproduction of intramolluscan stages, and represent a clone if a snail was infected with a single miracidium. Here we investigated cercarial clones of Himasthla elongata – namely, the infectivity of cercariae with normal (negative) and deviant (positive) photoreaction. In our study, most H. elongata clones showed intraclonal variance in their response to light. The proportion of photopositive cercariae ranged between 0.2% and 60% in different H. elongata clones. Photopositive larvae demonstrated significantly reduced rates of encystment in Mytilus edulis haemolymph in vitro and in young mussels. We discuss the possible mechanisms behind intraclonal variations, such as non-specific genomic rearrangements.

Fully developed, sexually mature small male and female acanthocephalans, Microsentis wardae Martin & Multani, 1966 (Neoechinorhynchidae) reaching only 2.25 mm and 2.42 mm, respectively, were collected from the rectum of longjaw mudsuckers, Gillichthys mirabilis Cooper, in the salty marches of Anaheim Bay and San Diego Bay, California. Our specimens were half the size of those reported in the original description from the same host in Scammon's Lagoon over 700 km to the south. The ratio of proboscis and receptacle size to trunk size was markedly higher in our specimens compared to the larger specimens measured in the original description. The anatomy of all structures in our specimens from Anaheim Bay was comparable to that of the larger Scammon's Lagoon specimens that have apparently realized more growth in the Scammon's Lagoon. We have observed more structures that are not reported in the original description, especially evident from our scanning electron microscopy images, which are not possible to observe in the original line drawings. In our specimens, the micropores were unusually widely spaced and the energy dispersive X-ray analysis showed longitudinal hook sections with high levels of sulphur and phosphorus and moderate levels of calcium, but the whole hooks showed highest levels of sodium and magnesium – the biochemical hook signature of this species. Sequences of the small subunit (18S) of the nuclear ribosomal DNA were generated and compared with acanthocephalan sequences available from GenBank. As M. wardae comprises a monotypic genus, therefore, phylogenetic analyses inferred from the 18S gene showed its relationship with other species of closely related genera of Eoacanthocephala. This is the first report of molecular data of M. wardae.

1. Presence of Molineus patens in England is recorded for the first time.

2. A more complete description is given of the morphology of M. patens including details of the spicules of the male and of some interesting papillae in the female tail.

3. The species of the genus Molineus are reviewed and compared and the suggestion is made that M. americanus is a synonym of M. patens.

Infective third-stage larvae of Dracunculus medinensis in cyclops have been maintained at 37°C in normal saline containing from 0·05 to 1·0% of hydrochloric acid. At acid levels normally met with in the human stomach 50% mortality of emerging larvae occurred in 150 minutes, suggesting that the time taken for larvae to pass through the stomach may be of importance in determining whether an infection is successful or not.

Dioctowittus denisoniae n. sp. from Denisonia punctata differs from D. wittei and D. chabaudi in the smaller size, lack of vestigeal male precloacal sucker, short egg-filaments, the presence of lateral expansions at the posterior end in the male, and in the expansions of the oesophageal tissue between the stichocytes. Dioctowittus sp. from Liasis amethystinus differs from the three described species in the possession of lateral lobes at both extremities.

Ichthybothrium ichthybori gen. et sp. nov. (Pseudophyllidea : Ptychobothriidae) is described and figured from specimens collected from the intestine of the African freshwater fish Ichthyborus besse from the White Nile near Khartoum, Sudan. Ichthybothrium and Ptychobothrium show some similarities but can be differentiated by the shape of the scolex and the position of the vitelline follicles. Ptychobothrium cypseluri Rao, 1957 and Plicatobothrium cypseluri Cable and Michaelis, 1967 are congeneric and a new name Plicatobothrium raoi is proposed for the former.

The majority of third-stage Ostertagia circumcincta larvae exposed to 0·5% levamisole failed to infect lambs even though the worms regained some activity after repeated washings in balanced saline. A low level of efficiency was recorded against 4·5-day-old O. circumcincta when lambs were treated with levamisole at 7·5 mg per kg. Nine-day-old worms from hosts which received anthelmintic on day 4·5 were at the same stage of development as those from untreated control lambs.

Recent collections of helminths from the clariid catfish, Clarias batrachus (L.) in India and Malaysia have included Bovienia serialis (Bovien), a species originally described by Bovien (1926) from a single whole specimen and fragments of others. The generic diagnosis formulated many years later by Yamaguti (1959) and based indirectly on one of these fragments has inevitably led to some confusion regarding the characters of the genus. With the collection of new material it is now possible to emend the generic diagnosis and redescribe the species.

Antechiniella septentrionalis n. sp. (Spirurida: Acuariidae) is described from the duodenum of a tundra vole, Microtus oeconomus (Pallas), collected in the Magadan region in the north-east part of Russia. It differs from A. suffodiax (Beveridge & Barker, 1975) and A. sertatum Smales, 1991 mainly in having a larger number of postcloacal papillae (5–6 pairs vs 4 pairs), a differently shaped left spicule, the disposition of precloacal papillae in two rows vs one, and oblong vs oval eggs. Other differences include the different disposition of ovaries in A. septentrionalis n. sp and A. suffodiax and the different structure of deirids in A. septentrionalis n. sp. and A. sertatum. The new species was characterized molecularly (partial sequences for 18S rRNA, 28S rRNA and cox1 mtDNA). The phylogenetic analyses performed showed the affinity of the new species to the members of the Acuariidae and other spirurid nematodes.

The large number of species of the genus Opisthorchis Blanchard, 1895 that have been reported from different regions of the world as parasites of dog, cat, man and lower groups of fish-eating vertebrates, have generally been identified on such adult morphological characters as the size or shape of the gonads, the position and shape of the excretory bladder and the character of the vitellaria, whether in acini or in linear distribution. The validity of the allied genera, Amphimerus Barker, 1911; Paropisthorchis Stephens, 1912 and Clonorchis Looss, 1907, proposed for some of these opisthorchids, had been questioned, among others, by Tubangui (1921), Morgan (1927), Baylis (1929), Faust (1930, 1949), Bhalerao (1935), Erhardt (1935), Wallace and Penner (1939), Price (1940), Dawes (1940), Bisseru (1957) and Watson (1960).

Chromosomal complements of an oocyte and a fertilized ovum from the ootype of Isoparorchis hypselobagri Billet, 1898 have been studied. Twenty diploid and 10 haploid chromosomes have been observed. In the karyotype the presence of five submetacentric, four acentric and a pair of sex chromosomes provide a significant cytotaxonomic information.

1. A preliminary account is given of certain serological investigations carried out on a rabbit fed with the embryonated eggs of Ascaris megalocephala.

2. By means of the complement-fixation test it has been shown that a definite immunity response occurs in the first five weeks of the infection.

Echidnotaenia gen. nov. (Anoplocephalata: Linstowiidae) is proposed for Cittotaenia tachyglossi Johnston, 1913 from the monotreme Tachyglossus aculeatus Shaw, 1792. The new genus is distinguished from other genera of the Linstowiidae by its paired genitalia and aporally extended vitellaria.

As far as the authors are aware, no standard technique has been described for the enumeration of infective trichostrongylid larvae recovered from faecal cultures. In experiments involving artificial infestations it is usually necessary to divide a concentrated suspension of larvae into a number of doses. In measuring the doses a dilution method may be used in which all the larvae in one or more aliquots taken from the diluted suspension are distributed on to a convenient number of slides and counted under the microscope. Alternatively, aliquots may be placed on the counting slide devised by Scott (1927). Such procedures are, however, time consuming and are fatiguing to the operator, where a large number of enumerations has to be made. They have the further disadvantage that the arbitrary dilution factor employed may result in too great a dispersion or conversely too great a concentration, either of which is undesirable from the point of view of accuracy and ease of counting.

Two new species of helminths, Fastigiuris prudhoei from Ochotona rufescens Gray, 1842, and Trichuris mofidii from Rhombomys opimus Lichtenstein, 1823, have been identified and described from mammals collected in Iran.

The distribution of cobalt in parasitic helminths belonging to the trematodes, cestodes or nematodes was determined by the use of an atomic absorption spectrophotometer. The results of these analyses have demonstrated that growing trematodes (smaller forms) with active oogenesis and spermatogenesis contained more cobalt than older forms (large or very old adults) with empty uteri and large lobulated testes. In cestodes, the neck region of cysticerci and immature proglottids of adults showed more cobalt than the cyst portion of cysticerci and hydatid or mature and gravid proglottids of worms. Similarly, the youngest endogenous daughter cysts of Echinococcus granulosus showed more cobalt in their walls than those of larger forms. The element was found more concentrated in nematode eggs than in adult females, irrespective of species of host.