A comparative study of the glandular and excretory systems of the oncomiracidia of the monogenean skin parasitesEntobdella hippoglossi, E. diademaandE. soleae

Abstract

A comparison of the oncomiracidia of the monogenean skin parasitesEntobdella hippoglossifrom the halibut (Hippoglossus hippoglossus), E. diademafrom the sting ray (Dasyatis pastinaca) andE. soleaefrom the skin of the common sole (Solea solea) has revealed the presence of ‘body gland cells’, all of which have openings on the ventral or lateral surfaces of the larvae. In all three species there are two pairs of glands lying in the posterior region of the body proper with long ducts extending into the haptor and opening on its ventral surface. In addition to these two pairs of glands there are seven other pairs of body glands inE. hippoglossi, six pairs inE. diademaand two pairs inE. soleae.InE. soleaeall the ‘body gland cells’ are poorly developed in the oncomiracidium and are more conspicuous in post-oncomiracidia. The fate of the ‘body gland cells’ during post-oncomiracidial development has been studied inE. soleae, and their possible functions are discussed. The glands in the head region (anterior median, posterior median and lateral head glands) are similar in all three species. Gland cells associated with the alimentary system are less easy to observe but differences between the three species appear to be small.In the oncomiracidia of all three species the number of flame cells and their distribution are the same, but the oncomiracidia ofE. hippoglossiandE. diademahave loops in the excretory ducts anterior to the bladder and the bladders ofE. diademacontain refringent bodies.The oncomiracidial eyes ofE. hippoglossiandE. soleaehave lenses but the lenses are greatly reduced in the oncomiracidia ofE. diadema.In the three larvae there are small but characteristic differences in the shapes of the accessory sclerites.The oncomiracidium ofE. hippoglossihas not previously been described.