For over six decades, the mainstream consensus in evolutionary immunology has maintained the central dogma that adaptive immunity—defined by clonal expansion, specific immunoglobulins, and dedicated lymphocytes—is an exclusive innovation of jawed vertebrates. This review synthesizes sixty years of structural, functional, and genomic evidence demonstrating that the sea star (Echinodermata) possesses a fully operational, primitive adaptive immune system. We detail the anatomical characterization of sea star B and T lymphocytes within ancestral lymphoid organs, trace the functional mechanics of the Invertebrate Primitive Antibody (IPA), and present modern genomic data confirming the existence of MHC-like networks. By systematically addressing the structural homologies between echinoderm and mammalian immune cells, this paper directly challenges conventional evolutionary dogmas and proposes a unified framework for the origin of adaptive immunity.