FINE-STRUCTURE OF THE DORSAL PAPILLAE IN THE HOLOTHURIOID HOLOTHURIA-FORSKALI (ECHINODERMATA)

The dorsal surface of the holothurioid Holothuria forskali bears sever al longitudinal rows of modified podia called papillae. Each papilla c onsists of a conical stem topped by an hemispherical bud. Their gross tissue stratification is the same all along the papilla being made up of four tissue layers, viz. an inner mesothelium, a connective tissue layer, a nerve plexus and an outer epidermis. The latter is differentl y organized according to whether it belongs to the stem or to the bud. The epidermis of the bud is built up by ciliated cells that intimatel y contact the nerve plexus and have the classical structure of echinod erm sensory cells. The papillae are thus sensory organs involved in me chanoreception and possibly chemoreception.