Fig. 1

Parasitized intestine of Esox lucius. a Sagittal section through the middle region of intestine with attached Acanthocephalus lucii (asterisk). There is contact between the parasite’s trunk and damaged intestinal folds. Intact folds distant from the parasite’s body can be seen on the left side of the figure. Arrows show mucus blanket, which surrounds the worm’s trunk. Alcian blue/periodic acid Schiff’s (AB/PAS) stained section. b Lack of intestinal folds at the site of attachment of A. lucii; the proboscis is visible, and proboscis hook (arrowhead) is embedded in the lamina propria-submucosa. Detached epithelium (curved arrow) is free in the lumen. A heavy layer of collagen (thick arrows) and several thinner collagen layers (arrows) are evident. AB/PAS stained section. c Semithin section shows two proboscis hooks (arrowheads) embedded in lamina propria-submucosa; several mast cells (arrows) near and far from hooks and collagen fibres (curved arrows) are visible. Toluidine Blue stained section. d Micrograph of semithin section of lamina propria-submucosa, arrowhead shows a capillary and many mast cells (arrows) around, collagen fibres (asterisks) are abundant in this layer. Toluidine Blue stained section. Abbreviations: LP, lamina propria-submucosa; M, muscle layer; SC, stratum compactum. Scale-bars: a, 200 μm; b, c, 100 μm; d, 10 μm