The present paper presents observations on the ecology and systematics of the Echiurida from Una Grande, Rio de Janeiro State, Brazil. Some hydrographic data like salinity, temperature, oxygen conten t and mean size of the sediment granulometry (Ø) are correlated with the occurrence of the Echiurida. A new species, Thalassema liliae is described. Lissomyema exilii (F. Müller) is recorded for the first time in this area. The zoogeographic distribution of the family Echiurida is also given.