Published online by Cambridge University Press: 06 April 2009
The male intromittent apparatus of Ergenstrema labrosi and Ligophorus angustus, monogenean parasites of the thick-lipped grey mullet Chelon labrosus, consists of a slender flexible penis tube with an expanded proximal region and whose distal end passes freely through a canal in an accessory sclerite; the tube is surrounded by a sleeve of longitudinal muscle and the apparatus works in a manner generally similar to an engineer's Bowden cable. There is a substantial difference in the form of the accessory sclerite in the two species. In both parasites there is a slender sclerotized vagina which, in L. angustus, is short and straight or curved but in E. labrosi is about 7 times longer and forms a spiral. The special role of the sclerotization of the distal part of the vagina may be to resist perforation of the wall by the exceedingly fine penis tube and the consequent discharge of sperms into the parenchyma.