, by reverse transcription polymerase chain reaction with the primers designed based upon the homologous cDNA sequence of Other primers were designed according to the partial sequence of two fragmentswere obtained using 3RACEand sequenced. Sequence analysis revealed a 904 bp cDNA containing an 81 bp 5untranslated regions, and 357 bp open reading frame putatively encoding a protein of 119 amino acids. The deduced amino acid sequence of MPwas subjected to BLAST search for similarity with published sequences and it was found that MPII shared high identity (81.51%) with Nereis diversicolor (77.12%), and with the hemerythrin of 3EX₁₆HX₃HX₂₃/₂₈HX₄D) of the hemerythrin familyPerinereis aibuhitensis for 12, 24, 48, and 72 h using quantitative PCR. The expression levels of 2+. The current study showed that the expression levels of the <0.01) than control group at 40 mg/L Cd²⁺ after 72 h. The level of mRNA produced in the muscle tissue of sandworm increased significantly following exposure to 5, 10, and 20 mg/L <0.05). Therefore, the expression level of the 2+. We suggest that heavy metal Cd²⁺ is associated with the induction of expression, and the present study provided molecular support for the assessment of early ecological risks for monitoring the marine sediment environment based on the health of clamworm.