A NEW GENUS AND SPECIES OF HETERONEMERTEAN FROM THE CHANGJIANG (YANGTZE) RIVER ESTUARY

A new genus and species of heteronemertean, Yinia pratensis gen. nov. and sp. nov., collected from low salinity waters (salinity 0.2-0.4%) a t Changjiang River Estuary, is described and illustrated. The species possesses a proboscis with an outer circular and an inner longitudinal muscle layer, and is placed in family Lineidae sensu Gibson. The foll owing combination of morphological features distinguishes the new spec ies from any other genera in this family: proboscis with two muscle cr osses; dermis without connective tissue layer between gland cells and body wall outer longitudinal muscle layer; rhynchocoel wall circular m uscles not interweaving with adjacent body wall longitudinal muscles; foregut with circular somatic muscles and subepithelial gland cell lay er; neurochord cells present in central nervous system; caudal cirrus missing; blood system developed into alimentary plexus extending almos t the full length of the body. Another significant character is that t he lobular excretory cells are extremely well developed which may repr esent adaptation to water of low salinity.