First, some species produce toxins that are of interest to pharmaceutical firms seeking to learn their medical value. Some compounds isolated to date exhibit antimicrobial activity or act as anti-inflammatory agents and anticoagulants. Fishermen in the Pacific islands use the toxins, some of which act as respiratory inhibitors, to entice fish and octopus from crevices so that they may be more easily speared. The most important feature distinguishing the sea cucumbers is a calcareous ring that encircles the pharynx or throat. This ring serves as an attachment point for muscles operating the oral tentacles and for the anterior ends of other muscles that contract the body longitudinally.
Sea cucumbers are also distinct as echinoderms in having a circlet of oral tentacles.
In some species, the ossicles may be enlarged and plate-like. Figure 1 . Mike Reich . Despite their similarity to the radial canals of other echinoderms, these latter structures arise embryologically in a quite different manner. In holothurians, the larval structures that would form the radial canals in other echinoderms instead become the five primary tentacles.