Pathogen size-dependent functional specialization of hemocytes in the giant centipede Scolopendra mutilans

Arthropods rely exclusively on innate immunity; however, cellular immune mechanisms in myriapods remain poorly understood. Here, we present a cell-type-resolved analysis of hemocyte-mediated immunity in the giant centipede Scolopendra mutilans. We established a long-term in vitro hemocyte culture system that combines live-cell imaging with functional immune challenges. Hemocytes were classified as granulocytes, plasmatocytes, and prohemocytes. Upon Escherichia coli exposure, granulocytes rapidly exhibited scanning behavior and served as the predominant phagocytic effector cells observed, completing engulfment and lysosomal activation within 1 h. In contrast, large particles such as Sephadex beads induced encapsulation and nodulation responses dominated by plasmatocytes, with early cooperative involvement of granulocytes. Differential hemocyte counts revealed a rapid reduction in circulating granulocytes, accompanied by an increase in prohemocytes during early infection. Pharmacological inhibition of microtubules impaired granulocyte pseudopodia formation and plasmatocyte spreading, indicating a cytoskeleton-dependent immune function. Together, these findings demonstrate pathogen size-dependent functional specialization of centipede hemocytes and extend arthropod cellular immunity beyond insect models.