Parasitic males usually found in the nephridium of the female. Family Bonellidae occurs widely and thier bathymetric range is extensive. All these worms are obligate deposite feeders, sorting detritus from the bottom surface. The 8 bathyal species are known as having single find with the exception of Eubonellia valida. The ansence of sexual dimorphism distinguishes the echiurids from the bonellids.
Longitudinal musculature is some genera is thicked to form longitudinal muscle bands.
Echiurids tend to inhabit shallow waters. Principal publications Beljaev G.M. Deepsea Oceanic Troughs and its Fauna. Zenkevich L.A. New Genus and two new species of deepsea Echiurids from the Pacific Ocean. On the Sipunculans and Echiurans Fauna of Mediterranean and Iberian Basin. Murina V. V. A New Species of the Bonnelidae and a New Finding of an Echiurid.