Global warming is a reality and its effects havebeen widely studied. However, the consequences for marineinvertebrates remain poorly understood. Thus, thepresent study proposed to evaluate the effect of elevatedtemperature on the innate immune system of Antarctic seaurchin Sterechinus neumayeri. Sea urchins were collectednearby Brazilian Antarctic Station ‘‘Comandante Ferraz’’and exposed to 0 (control), 2 and 4C for periods of 48 h, 2,7 and 14 days. After the experimental periods, coelomicfluid was collected in order to perform the followinganalyses: coelomocytes differential counting, phagocyticresponse, adhesion and spreading coelomocytes assay,intranuclear iron crystalloid and ultra structural analysis ofcoelomocytes. The red sphere cell was considered a biomarkerfor heat stress, as they increased in acute stress.Besides that, a significant increase in phagocytic indexeswas observed at 2C coinciding with a significant increaseof intranuclear iron crystalloid at the same temperature andsame time period. Furthermore, significant alterations incell adhesion and spreading were observed in elevatedtemperatures. The ultra structural analysis of coelomocytesshowed no significant difference across treatments. Thiswas the first time that innate immune response alterationswere observed in response to elevated temperature in a Polar echinoid.