Morphological investigations of microdrile oligochaetes (Annelida, Clitellata) using scanning electron microscopy

Over the past several years, the authors of this work have investigated external structures of microdrile oligochaetes using scanning electron microscopy (SEM). Both published and still-unpublished data have revealed new structures of interest, especially those associated with mating, ciliate sense receptors, chaetae, and dorsal pores. Mating systems can be classified in 3 categories: grasping, coupling, and embracing. Ciliate sense receptors can be classified as poorly defined (unelevated), sensory buds, or papillae, and are provided with blunt cilia and/or sharp cilia. They are present along the whole body (including clitellum, budding, and regeneration zones), scattered on the prostomium, peristomium, and pygidium, arranged in transversal rows and scattered in chaetal segments. Somatic chaetae show great variability when observed by SEM. Hair chaetae are at least potentially provided with denticulations. Dorsal pores were observed in aquatic microdriles. SEM proves to be an invaluable tool to discover important structures associated with functional anatomy in microdriles.