The oncomiracidium of Oculotrema hippopotami Stunkard, 1924 and relationships within the Polystomatidae (Monogenea)

Exceptional occurrences have fundamental interest in evolution relevant to understanding adaptations and origins. Monogeneans primarily infect aquatic lower vertebrates, i.e. fish, amphibians and chelonian reptiles, but there is a single instance of colonisation of a mammal: Oculotrema hippopotami Stunkard, 1924 infecting the eye of Hippopotamus amphibius Linnaeus. Its combination of systematic characters is amongst the most diverse in the Polystomatidae Gamble, 1896 and relationships are obscure. This study emphasises the primary significance of two features: the reinforcement of haptoral suckers with an internal skeleton and the pattern of ciliated cells on the oncomiracidium, especially the presence of conjoined cells. Closest relationships are with polystomatids infecting chelonians, specifically species of Polystomoides Ward, 1917 from the oral cavity/pharynx, or more likely (but with currently incomplete evidence) species of Neopolystoma Price, 1939 from the eye. Morphological characters of polystomoidines, all of which infect chelonians, appear to have remained relatively stable since at least the Jurassic (from zoogeographical evidence), but the highly derived characters of species of Oculotrema may have evolved during the comparatively short period (16 million years) since the Miocene origin of Hippopotaminae Gray. However, the initial host switch may plausibly have been to hippo ancestors, the anthracotheres, with similar semi-aquatic ecology and an Eocene origin (41 million years ago). Over the same time-scale, the oncomiracidial cell pattern remained closely comparable with that of presumed ancestors, emphasising its value in phylogenetic analyses.

Oviposition, hatching and the oncomiracidium of Eupolystoma anterorchis (Monogenoidea)

Eupolystoma anterorchis Tinsley, 1978, infects the urinary bladder of Bufo pardalis at the Cape, South Africa. Reproduction occurs throughout the year but the eggs are not deposited continuously: up to 300 are retained in the long uterus of the parasite and may develop to the point of hatching. The eggs are deposited intermittently en masse. The stimulus for deposition appeared to be osmotic, since worms transferred from the host's bladder into freshwater released their stored eggs. However, in simple experiments where hosts were transferred from dry land to water such egg deposition did not follow and the stimulus requires further investigation. Once discharged from the uterus the oncomiracidia hatch rapidly both in water and in host urine. Those eggs immediately expelled from the bladder at urination release larvae which can infect the same or other host individuals via the cloaca. But when eggs are deposited in the bladder between successive host urinations larvae can emerge and attach themselves directly to the bladder wall. These larvae develop to maturity alongside their parents, and this internal re-infection can give rise to massive levels of infestation. The distributions of the tegumental ciliated cells and sensillae of the oncomiracidium have been determined with silver impregnation. There are 55 ciliated cells whose pattern corresponds with that of Polystoma species except for the orientation of three dorsal cephalic cells. The distributions of their tegumental sensillae show greater divergence and the Eupolystoma larva lacks the hamulus primordia typical of Polystoma.

Chaetotaxy applied to Norwegian Gyrodactylus salaris Malmberg, 1957 (Monogenea) clades and related species from salmonids

Gyrodactylus salaris Malmberg, 1957 is a major pathogen of wild Salmo salar L. parr populations in Norway, and its delimitation from non-pathogenic species is important. The present study was undertaken to test the power of chaetotaxy to differentiate between three populations belonging to both the same and different clades (as stated by mtDNA) of G. salaris, in addition to three different species of gyrodactylids (G. salaris, G. thymalli and G. caledoniensis). The gyrodactylids were processed for chaetotaxy in situ and a maximum of 50 specimens per collection site were used to construct a generalised map over the sensilla. The sensilla were found in all populations to be symmetrically distributed around the median longitudinal axis, according to a formula of 7 dorsal (34 sensilla) and 8 ventral (44 sensilla) clusters on each side of the median line. The three Norwegian populations of G. salaris were found identical, as were the population of G. thymalli. The specimens of G. caledoniensis from Scotland, however, were found to differ from the Norwegian species G. salaris and G. thymalli by the position of one sensillum in two of the clusters. A comparison of the sensillum pattern of laboratory maintained G. salaris (River Lierelva) with results obtained ten years earlier, questions the temporal stability of the chaetotaxy pattern. The present results indicate that chaetotaxy can be used to discriminate between certain Gyrodactylus spp. but not generally.

Chaetotaxy of the monogeneans Macrogyrodactylus clarii and m. congolensis from the gills and skin of the catfish clarias gariepinus in Egypt, with a note on argentophilic elements in the nervous system

A comparison has been made between the chaetotaxy of the gyrodactylid monogeneans Macrogyrodactylus clarii Gussev, 1961 and M. congolensis (Prudhoe, 1957) Yamaguti, 1963 from the gills and skin, respectively, of the catfish Clarias gariepinus (Burchell) from the river Nile in Egypt. Bilaterally arranged argentophilic structures on the surface of these parasites are presumed to be sensilla and are more abundant in M. clarii than in M. congolensis especially on the ventral surface (124 vs. 66). In both species these sensilla are concentrated on the head lobes and in the pharyngeal region, but there are features of the sensilla patterns that can be used to distinguish the two species. Comparison is made with sensilla patterns of other gyrodactylids. A system of cells and dendritic processes, most probably part of the nervous system, also has an affinity for silver in the two species. There are no previous records of extensive argentophilic elements in the nervous systems of monogeneans.

Larval and post-larval development of Ergenstrema mugilis Paperna, 1964 (monogenea, ancyrocephalidae) parasite of Liza ramada (Risso, 1826) (teleostel, mugilidae)

The ciliated cells, chaetotaxy and excretory system of the oncomiracidium are fully described in Ergenstrema mugilis Paperna, 1964. The study of the post larval development shows a phase of cutaneous infestation in the fish host and the mode of transmission is discussed among Dactylogyroidea. The morphogenesis of the parasite haptor is described. The origin and migration of the hamuli in Dactylogyroidea are discussed.