Stalked barnacles of the genus Octolasmis Gray 1825 (Poecilasmatidae) are sessile invertebrates frequently found attached to decapods mainly in the branchial chambers of crabs. The main factors that determine the settlement and the distribution of stalked barnacles are water flow, which affects food availability, ventilation and removal of metabolites. Octolasmiscor was found attached on the external mouthparts, carapace margins and gill chambers of the crabs. This observation of Octolasmiscor attached to Scylla serrata is the first time record from the diamond harbour of West Bengal.