Triops is a genus of small crustaceans in the order Notostraca (tadpole shrimp). Some species are considered living fossils, with a fossil record that reaches back to the late Carboniferous, 300 million years ago. One species, Triops longicaudatus, is commonly sold in kits as a pet.
Innate immunity is found in both animals with and without adaptive immunity. The molecular components of the innate immune system do not appear to be closely related to the molecules of the adaptive system.
The innate immune response is not completely nonspecific, as was originally thought, but rather is able to discriminate between self and a variety of pathogens. The innate immune system recognizes microorganisms via a limited number of germline-encoded pattern-recognition receptors (PRRs). This is in contrast to the large repertoire of rearranged receptors utilized by the acquired system. PRRs possess common characteristics.