B. gracilis may refer to: * , a species of gram negative anaerobic bacterium * , a liverwort species in the genus Barbilophozia * Bathysauropsis gracilis, the black lizardfish, a grinner * Belonolaimus gracilis, the pine sting nematode, a plant pathogenic nematode * Bletia gracilis, a species of orchid * Bolitoglossa gracilis, a species of salamander in the family Plethodontidae endemic to Costa Rica * Bomarea gracilis, a species of plant in the family Alstroemeriaceae endemic to Ecuador * Bouteloua gracilis, the blue grama, a long-lived, warm season, C4 perennial grass * Brunneria gracilis, a species of praying mantis found in Argentina, Brazil, Paraguay, Uruguay and Venezuela