Their habitat is in the spaces between marine gravel to which they attach themselves. They are among the most recently discovered groups of Metazoans.[7] They attach themselves quite firmly to the gravel, and this explains why they remained undiscovered for so long.[5] The first specimen was collected in the 1970s, and later described in 1983.[7] They are found at all depths of water, in different sediment types, and in all latitudes.[5] They have not yet been found in the fossil record.