The effects of parasitism by larval Digenea on the digestive gland of the intertidal prosobranch, Littorina saxatilis (Olivi) subsp. tenebrosa (Montagu)

Abstract

The effects of parasitism by five species of larval Digenea on the digestive gland cells of Littorina saxatilis (Olivi) subsp. tenebrosa (Montagu) were investigated by comparing histochemically stained cells in healthy, starved and parasitized animals.Two distinct effects were apparent: (a) The germinal sacs compress the walls of the digestive gland tubules and block the lumen. Since food cannot pass this block, digestive gland cells behind undergo starvation autolysis. (b) In digestive gland tubules not cut off from their food supply, glucose, glycogen, glycoproteins and lipid food storage globules are reduced and there is a compensatory increase in the number of food vacuoles in the digestive cells; an increase in glucose but a decrease in glycogen in the visceral haemocoel; and an increase in the number of secretory cells, perhaps in order to eliminate the parasite's excretory products from the visceral haemocoel.