Report on the occurrence of abnormal four-armed red-knobbed starfish Protoreaster linckii (Echinodermata: Astroidea), Tuticorin coast, south-east coast of India

Starfish are echinoderms that live among corals and occur from the supra-littoral to the hadal zone. Deviation from pentamerism is a rare phenomenon in starfish and was observed in the red-knobbed starfish (Protoreaster linckii) collected from the Tuticorin coast, India. Eighty-five specimens were collected and, among these, one was found to be abnormal and had only four arms. The reasons for this abnormality may be due to the changes that occur during larval metamorphosis or caused by an abnormal regeneration of the arm.