How does the sea squirt's immunological setup contrast with that of mammals?

It lacks many specific immune system genes typical of vertebrate protection.

Sea squirts, or tunicates, present an immunological setup that contrasts sharply with vertebrates like mammals. Mammals possess extensive, genetically coded internal defense systems, often involving numerous specific immune system genes. In contrast, sea squirts appear to be missing many of these standard vertebrate defense genes, suggesting they utilize an alternative or more primitive strategy for survival against pathogens in pathogen-rich environments. This fundamental absence forces researchers to re-examine basic principles of host defense mechanisms and how life defends itself against disease without relying on the typical vertebrate genetic blueprint.