Ultrastructure of the digestive and protonephridial systems of the metacercaria of euclinostomum multicaecum
The structure of the digestive tract of Euclinostomum multicaecum (Digenea: Euclinostomatidae) is unusual, comprising several main lateral caeca which extend posteriorly and further divide, giving rise to numerous smaller branches which are widely distributed throughout the fluke. These multicaeca presumably promote nutrient absorption during rapid and prolonged feeding directly following excystment. The caecal wall consists of a syncytial gastrodermal epithelium, bearing loop-like lamellae which extend into the lumen and enclose spherical inclusion bodies and presumably also, increase the absorptive surface area. There was no evidence of endo- or exocytosis, nor were lysosomes, phagosomes or residual bodies observed. The gut caeca are supported by a fibrous basal lamina and an underlying layer of muscle fibres, while parenchymal cells occupy much of the extracellular space. The protonephridial system resembles that observed in other digeneans consisting of flame cells and collecting ducts which join to form a bladder that opens externally through a single excretory pore. The syncytial epithelium of the collecting ducts is elevated by numerous lamellae while the basal lamina is highly infolded. The luminal contents of these ducts comprise bar-shaped crystalline structures, lipid droplets and electron-dense inclusion bodies. The excretory system is supported by a network of muscle fibres and parenchymal cells.
School of Biology and Biochemistry, The Queen's University of Belfast, Belfast, BT9 7BL, UK:
P
Ramasamy
GP
Brennan
K
Stalin