The present study was carried out on the earthworms Aporrectodea trapezoids collected from Bezeh-Betas (Zakho City). The study aimed to classify the earthworm species using molecular tools and focusing on the effect of some agonists on the contractility responses of crop and gizzard smooth muscle cells. The molecular classification was performed using mitochondrial COX 1 gene as a DNA marker, and the DNA was extracted from the crop and gizzard tissues of the earthworm and amplified using universal primers (forward primer LCO14900 and specific reverse primer SPE-CO1-A25), and Touchdown Polymerase Chain Reaction T-PCR has used the size of the band obtained from the amplification of COX1 gene was 523 bps. Out of 45 PCR products, five were sent to Macrogen Company (South Korea) for DNA sequencing. The sequencing results were submitted to BioEdite program for sequence alignments. The obtained sequence confirmed that the species is Aporrectodea trapezoids, and this sequence was deposited in GeneBank under the accession number (MW354675). Phylogenic analysis of Aporrectodea trapezoids COX1 indicated its relationship to other strains from the USA. Regarding the response of crop and gizzard smooth muscle cells to some agonists, such as Hydrogen sulfide, Nicotine, Sodium nitroprusside, and Norepinephrine was recorded. The isolated crop and gizzard smooth muscle isolated from earthworm were fixed in Panlab multi-chamber organ bath system containing ringer solution for recording the amplitude and frequency contractions of crop and gizzard. The crop and gizzard were left in Ringer solutions for 20 minutes for tissue stabilization, followed by its exposure to different doses of Sodium Nitroprusside (1X10-6 to 1X10-3 M), Norepinephrine (1X10-8 to 1X10-3 M), Nicotine (1X10-8 to 1X10-5 M), and Hydrogen sulfide (1-5 mM) then half-maximal inhibitory concentration (IC50) were determined for crop and gizzard smooth muscle. The obtained results revealed that different doses of norepinephrine, Hydrogen sulfide, and nicotine significantly reduced the amplitude and frequency of contraction of crop and gizzard smooth muscle, which indicates that norepinephrine, Hydrogen sulfide, and nicotine are acting as inhibiting agents. On the other hand, treatment with different doses of sodium nitroprusside showed the non-significant effect on the amplitude and frequency of contraction of crop and gizzard smooth muscle of earthworm.