Sea cucumbers (Holoyhuroidea) class of the phylum Echinodermata (see Echinoderms). Body without arms, anus and mouth at opposite sides. The body is five-sided symmetrical with a much prolonged axis. Skeletal plates or ossicles in the skin are microscopic small. There are rows of podia on the body, and a circle of branched tentacles around the mouth for collecting fine food particles from the water or the sediment. They crawl on the sea bed or live buried in the mud, but there are some pelagic deep-sea forms.