Echinostoma revolution (Froelich, 1802) Looss, 1899 and Isthmiophora melis (Schrank, 1788) Lühe, 1909 (Echinostomatinae, Digenea): Scanning electron microscopy of the tegumental surfaces

ABSTRACT A detailed study of the surface topography of the echinostomes Echinostoma revolution and Isthmiophora melis has been carried out using SEM. The tegument of the body surface has a cobblestone-like appearance with interspersed pits. The presence of possible secretory granules is noted. Observations of the anterior end reveal that the collar spines are retractable. An unusual structure is described from the ventral gap of the spiny collar of E. revolutum. The origins of this structure and the possible functions of the spiny collar are discussed. The shape and distribution of body spines is described. Differences in cirrus morphology for the two species are described. The taxonomic position of, I. melis and the significance of cirrus morphology as a useful taxonomic character are discussed. Four types of presumed sensory or secretory structures occur—ciliated, domed, button and bilobed papillae. Their distribution is described and possible functions discussed.

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