ABSTRACT
Regular echinoids possess five fleshy pharyngeal protuberances (paradental tongues) which extend into the oral cavity and work like typical tongues. Each of these tongues is provided with an internal support (paradental axis)- which shows a peculiar chordoid structure. In fact, it mainly consists of glycogen containing vesiculate cells and slim muscle fibres. The structural features of these paradental axes, their anatomical relationships with the foregut and their supporting role suggest comparisons with different types of chordoid organs found in Deuterostomata and in Protostomata. The possible derivation of this type of chordoid tissue, never described before in echinoderms, is here discussed.
