Cellular organization and phylogeny of Cryptonaiada gen. n. (Cryptonaiadidae fam. n.) shed light on the evolution of intracellular vertebrate parasitism in Apicomplexa.

Cryptonaiada temporariae is the first known gregarine apicomplexan to evolve intracellular vertebrate parasitism, with 100% of its oocysts developing within tadpole macrophages.

• Why it matters: Understanding how parasites adapt to infect vertebrate hosts with complex immune systems is crucial for revealing key steps in parasitism evolution, yet little is known about early-branching lineages like Cryptonaiada.
• What they did: The study isolated and examined Cryptonaiada temporariae from tadpoles, analyzing its ultrastructure, host interactions, and phylogenetic placement using multi-gene analyses, establishing a new genus and family.
• The result: Findings suggest Cryptonaiada develops within macrophages during a host developmental window of immune immaturity, offering insights into early vertebrate parasitism and host-parasite coevolution.