Fig. 1

a The intestinal mucosa of the infected Squalius cephalus is covered by a thick blanket of mucus positive to alcian blue (AB). b Intestinal wall of a specimen of S. cephalus parasitised by the acanthocephalan Pomphorhynchus laevis which has penetrated through all the tissue layers of the intestine. The extroversible open bulb with hooks (B) is surrounded by fibrous inflammatory tissue, while the neck (N) at the point of attachment has disrupted the muscle layers of the host (m), and the body of parasite (P) impairs the intestinal folds, which show a high number of mucous cells in its epithelium (arrows). c Intestinal mucosa of an uninfected S. cephalus with a low number of mucous cells containing either acid (thin arrows), neutral (arrowheads) or mixed glycoconjugates (thick arrows). d High magnification of the intestinal epithelium in close proximity to the parasite (P) showing a high density of acid (AB-stain, thin arrows), and mixed (AB-periodic acid Schiff stain, thick arrows) glycoconjugates in the mucous cells. Scale bars 100 μm