C3 in Pomacea canaliculata: a conserved effector with developmental and immune roles.

C3 is the central effector of the complement system and one of the most conserved molecules of metazoan innate immunity. Despite its relevance, little is known about complement components in Lophotrochozoa. Here, we characterise the C3 ortholog of the freshwater gastropod Pomacea canaliculata (PcC3) using long-read transcriptomics, phylogenetics, expression profiling and immunohistochemistry. PcC3 displays a fully conserved domain architecture and clusters phylogenetically in agreement with metazoan relationships. Following LPS challenge, PcC3 is up-regulated in haemocytes and unexpectedly in the ampulla, but not in the posterior kidney, revealing functional specialization of immune tissues. Early developmental transcriptomes reveal strong and sustained PcC3 activation from 3 to 9 dpf. These data suggest that PcC3 retains canonical immune functions but may also contribute to developmental and homeostatic cell clearance, supporting P. canaliculata as a valuable model for complement biology in molluscs.