I found this species under the rock by attaching firmly. Its almost around 7-8 cm long. Collected along the coast of southern Tamilnadu. The body was so soft feels like worm. Help me to identify this.
I agree with the previous answers, it seems to be a sea cucumber indeed. You should find someone specialized in echinoderms in India that can tell you which species. I found some references to Holothuroidea from India, but I did not recognize this species (I am not a specialist in Echinodermata, however). It may be a juvenile form.