This study examined genetic diversity and gene flow in populations of Ophryotrocha worm species found on whale, cow, and pig bones in the Mediterranean Sea at different depths. DNA analysis of over 600 base pairs of the COI gene from 43 specimens formed two distinct branches - one containing worms from shallow depths under 20m, and one containing worms only from 57m deep. The branches showed 7.33-8.19% genetic distance, suggesting two cryptic species. Shallow samples showed high haplotype diversity with 21 haplotypes across locations, indicating gene flow between shallow populations. Deeper samples had lower diversity, supporting environmental influences on genetic structure.