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1

Egg variability, hatching and anatomy of the oncomiracidia of three Quadriacanthus species [Monogenea] from the Nile Delta catfish, Clarias gariepinus

100%
Reda E. S., El-Naggar M. M., Arafa S. Z.
Acta Parasitologica
|
2003
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tom 48
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nr 4
An account has been given of the egg variability, egg development, egg hatching and behaviour and anatomy of the oncomiracidia of three species of the genus Quadriacanthus, monogeneans parasitizing the gills of the catfish Clarias gariepinus inhabiting Nile Delta waters in Egypt. Each of the three species of the genus Quadriacanthus produces eggs of different shapes and sizes. Quadriacanthus clariadis clariadis and Q. allobychowskiella produce four types of eggs while Q. aegypticus produces nine types of eggs. All types of eggs differ from each other in the presence or absence, size and shape of the appendages. It is suggested that eggs of different types are not genetically determined or functionally different. There is no significant increase in the egg size during incubation. Fluid-filled sacs are found only in the fully developed eggs of Q. c. clariadis and Q. aegypticus; they are absent from eggs of Q. allobychowskiella. It is suggested that opening of the operculum and emergence of the oncomiracidium are brought about by a mechanical, chemical and/or osmotic hatching mechanism. The glandular system of the oncomiracidia of the genus Quadriacanthus includes two anterior median head glands, at least six lateral head glands constituting the anterior adhesive apparatus and four posterior body glands. Two crescent-shaped sclerites, representing the precursors of the ventral hamuli, are present in the haptor of the oncomiracidium of Q. allobychowskiella but these sclerites were not observed in the oncomiracidia of Q. c. clariadis and Q. aegypticus.
2

Ultrastructure of the egg and epidermis of the oncomiracidium of Zeuxapta seriolae [Meserve, 1938] [Monogenea, Polyopisthocotylea, Axinidae]

80%
Rohde K.
Acta Parasitologica
|
1998
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tom 43
|
nr 4
Scanning electron-microscopic (SEM) studies of the egg and oncomiracidium of Zeuxapta seriolae showed the following: the egg has a single filament at the pole opposite the operculum, its surface is smooth except for small rounded protuberances on the shell, and the fracture line between operculum and shell of the main part of the egg has numerous irregular transverse elevations. The non-ciliated surface of the oncomiracidium has many irregular folds, and ciliated cells bear many short microvilli between the cilia. Cilia taper towards the tips. Transmission electron-microscopic (TEM) studies of the cilia and epidermis of the oncomiracidium showed that both ciliated cells and non-ciliated epidermis are nucleated, in contrast to findings on Monopisthocotylea. Ciliated cells are separated by lateral cell membranes connected by septate junctions, there are surface microvilli, many cristate mitochondria, and cilia have single horizontal (anteriorly directed) hollow rootlets. In the ciliary tips, the number of microtubules gradually decreases, and apical parts of cilia have a diameter of about 1/4 of that of the more basal parts. The non-ciliated epidermis also contains mitochondria, as well as deep evaginations of the basal lamina. Phylogenetic implications are discussed. Presence of nuclei in the larval epidermis cannot be due to delayed shedding of nuclei as a result of neotenic development as suggested for polystomes, because Zeuxapta does not have neotenic development. It may be a synapomorphy of the Polyopisthocotylea. Further studies of additional species must show whether tapering ciliary tips and a reduction in the number of axonemal microtubules are a synapomorphy of all Monogenea, and whether presence of false vertical rootlets of epidermal cilia is a synapomorphy of the Monopisthocotylea.
3

Ultrastructure of the protonephridial system of the oncomiracidium of Zeuxapta seriolae [Meserve, 1938] [Monogenea, Polyopisthocotylea, Axinidae]

70%
Rohde K.
Acta Parasitologica
|
1997
|
tom 42
|
nr 3
Flame bulbs are formed by interdigitating terminal and proximal canal cells. There are many internal but few (or no) external leptotriches. The proximal canal has a septate junction and a reticulate (vacuolated) wall. The internal surface area of the distal capillaries (and possibly of parts of the proximal capillaries) is increased by lamellae. The cilia of the flame bulb and the lateral flames are few, and there is no well defined excretory bladder. The terminal part of the distal capillary is in contact with the surrounding surface epidermis by a septate junction. Flame bulbs of the oncomiracidium of Zeuxapta differ from those of adult monogeneans mainly in their smaller size and a smaller number of cilia. Comparative analysis of literature data shows that there is an increase of the number of cilia in the flame bulbs of monogeneans with increasing body size to a size of about 2.5 mm² (length x maximum width).
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