To investigate the molecular characteristics of the heat shock cognate protein 70 (HSC70) gene in the echiuran worm Urechis unicinctus, the full-length complementary DNA (cDNA) sequence of HSC70 in U. unicinctus was cloned and characterized. Additionally, the expression of HSC70 in different tissues of U. unicinctus was detected after exposure to 0.25, 0.75, and 1.25 mg L