Procamallanus (Spirocamallanus) halitrophus (Fusco and Overstreet, 1978) is an intestinal parasite of the flounders Syacium papillosum and Citharichthys macrops, both of which are native to waters off the coast of the state of Rio de Janeiro, Brazil. With transmission electron microscopy, we observed the body wall which is composed of the cuticle, hypodermis, and somatic musculature. The cuticle of P. (S.) halitrophus is composed of 5 layers: the epicuticle, cortical, median, fibrous, and basal layers. Underlying the cuticle is the hypodermis, a syncytium that contains mitochondria, glycogen granules, vesicles, inclusion bodies, and an endoplasmic reticulum. The region of hypodermal chords contains a nucleus in addition to the other organelles and there is a basal lamina surrounding each muscle cell. The use of imidazolebuffered osmium tetroxide solution revealed the presence of lipids in the epicuticle, the membrane that surrounds each muscle cell, the inclusion bodies, and the endoplasmic reticulum. The phosphotungstic-acid technique revealed basic proteins in the epicuticle and dense bodies. The use of periodic acid-thiosemicarbazide-silver proteinate for carbohydrate detection did not show any reaction products in the cuticle. However, glycogen particles were evident in the hypodermis and muscle cells.