Sea cucumbers are frequently among the largest and most diverse classes of benthic invertebrate in the intertidal and subtidal and constitute the vast majority of total biomass in slope and abyssal benthic systems. While most sea cucumbers are either sedentary or at the least comparatively slow-moving, a number of species move periodically by swimming and a few are primarily bathypelagic free swimmers. Holothurians have a calcareous ring at the anterior surrounding the esophagus, the ring consists of calcareous plates and serves as attachment for tentacle complexes and longitudinal muscles which extend along the body. The class differs from other echinoderms in its possession of a comparatively well-developed heamal system. Current commercial and experimental aquaculture of sea cucumbers, presumably as a result of accessibility and commercial value, is limited to high-value intertidal and subtidal aspidochirotes, primarily the temperate species A. japonicus and the tropical species Holothuria scabra.