Anatomie comparée des racines des rhizocéphales Sacculina carcini Thompson et Loxothylacus panopei (Gissler) parasites respectifs des brachyoures Carcinus maenas (L.) et Rhithropanopeus harrisii (Gould); étude ultrastructurale des racines libres

A comparative examination of the free roots of Sacculina carcini, parasitizing Carcinus maenas, and Loxothylacus panopei, parasitizing Rhithropanopeus harrisii, shows numerous similar ultrastructural features as well as a few specific variations. Proceeding inwards from the outside, the following structures can be seen: (1) a thin and uncalcified exoskeleton with irregular processes fitted with vesicules forming a dense network and opening in the host's haemocoel; the whole may also display deep infoldings, these characters promote an important increase of the root surface; (2) subcuticular spaces sometimes particularly developed; (3) root cells that show a double aspect.In periphery, the electron-lucent cytoplasm with microtubules and free ribosomes, show apical villi which can penetrate the exoskeleton; mitochondria are abundant and possess a dense matrix with parallel cristae. Near the axis of the root, an electron-dense cytoplasm contains numerous rough-surfaced endoplasmic reticulum cisternae and large reserve inclusion bodies. Pictures of cytolysis are visible at the edge of cells. Middle lumen seem to appear after degeneration of some axial cells. Peculiarities of the described structures and their respective role in the absorption of substances, storage of reserves, or excretion of metabolites are discussed with regard to the host–parasite relationships.