Involved in aggregate formation and phagocytosis by larval mesenchyme cells and adult coelomocytes. Binds to bacteria and may act as an opsonin in the innate immune system. From the mid-gastrula stage, expressed only in mesenchyme cells that are migrating toward the body wall. At the brachiolaria stage, expressed in presumptive coelomocytes of the coelomic pouch. Also expressed in adult coelomocytes (at protein level). During larval development, expression is first detected in the mid-gastrula stage and increases thereafter (at protein level). By bacterial challenge in adult coelomocytes.