Cynolebias is a genus of annual killifish endemic to Brazil, part of the seasonal-pool killifish radiation that fills temporary wetlands across the country's lowlands. The defining trait of the genus, shared with its close relatives, is an annual life history: adults live in shallow pools that dry out completely each year, and before the water disappears the fish bury fertilized eggs in the mud, where development pauses in diapause through the dry season and resumes only when rain refills the pool. The atlas's 10 species run 1.5–6 in, larger on the whole than many annual killifish, with the strong sexual dimorphism typical of the group - males patterned in blues and blacks with pale spotting, females plainer.
The common name "pearlfish," attached to several atlas species including the magnificent pearlfish (C. magnificus) and Brazilian pearlfish (C. porosus), reflects the fine speckled patterning many males carry. Cynolebias is a specialist's fish rather than a trade staple: killifish hobbyists propagate it by spawning pairs into peat moss, storing the peat through a simulated dry season, and rehydrating it to trigger hatching - the same technique used for annual killifish worldwide. Because each species is often tied to a small cluster of pools rather than a river system, habitat loss hits hard and fast; three of the atlas's ten species are assessed Endangered, a heavy tally for a genus this size and a sign of how vulnerable temporary-pool specialists are to land conversion in Brazil.