HOLOTHUROIDEA HAVE SPONGY BODIES HOMOLOGOUS TO SPONGY BODIES OF ECHINOIDEA AND TIEDEMANN’S BODIES OF ASTEROIDEA

In the holothuroid Chiridota laevis (O. Fabricius, 1780), we have found the organs that can be considered as homologues of the spongy bodies of sea urchins and the Tiedemann’s bodies of sea stars. The spongy bodies of C. laevis are located in the interradii and are formed by outgrowths of coelomic canals that connect the water ring with the coelomic cavities of the tentacles. Haemocoelic lacunae are adjacent to the coelomic outgrowths. The spongy bodies of sea urchins and the Tiedemann’s bodies of sea stars are also located in the interradii and indicate the position of the reduced tentacles. We suggest that the spongy bodies of echinoderms function as excretory organs (additional kidneys). Since the water-vascular system of most holothuroids does not open outwards, the spongy bodies of holothuroids are much smaller than those of other echinoderms and can be considered as rudimentary organs.

Echinodermata, interradii, tentacles, sea cucumbers, sea urchins, sea stars