Swallowing of sea water and its role in egestion in the monogenean Entobdella Soleae, a skin parasite of the common sole (Solea solea), with observations on other monogeneans and on a freshwater temnocephalan

Abstract

Swallowing sea water plays an important part in the process of egestion in several, epidermis-feeding, monogenean parasites from the skin and gills of fishes. In Entobdella soleae, from the skin of the common sole, Solea solea, the retracted pharynx acts as a peristaltic pump, forcing sea water into the branched and blind-ending intestine, inflating the gut diverticula and providing a suspension medium for debris from the digestive process. This secondary role for the pharynx has not previously been recorded. Inflation of the gut extends the muscles lying beneath the gastrodermis, and possibly neighbouring parenchymal muscles, permitting them to contract. This expels the sea water and flushes out the debris from the gut via the mouth. In E. soleae, the myofibrils associated with the gastrodermis appear to have narrower thick filaments than nearby parenchymal myofibrils. A similar series of swallowing movements, involving consecutive contractions of the pharynx followed by an egestion event, has been observed in the freshwater temnocephalan ectosymbiont Craspedella sp., from the gills of the Australian crayfish Cherax quadricarinatus.

Keywords :

• Monogenea
• Entobdella soleae
• Benedenia
• Temnocephala
• Craspedella sp.
• swallowing
• egestion
• pharynx
• myofibrils