Their habitat is in the spaces between marine gravel to which they attach themselves. They are among the most recently discovered groups of Metazoans. They attach themselves quite firmly to the gravel, and this explains why they remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths of water, in different sediment types, and in all latitudes. They have not yet been found in the fossil record.