The genus Eustra Schmidt-Goebel, 1846, includes 22 species from Southeast Asia, generally humicolous, but some of them being cavernicolous. All these species present neotenic features in the female genital apparatus: the female genitalia are orthotopic (i.e. gonopore located on the 7 th abdominal segment), and the gonostyle is present (but absent in all other adephagan Coleoptera, without exception). The possible correlation between the cave-dwelling life and this partial neoteny is briefly discussed, but with a remarkable fact: in the evolution of Eustra, the neotenic features appeared before the colonization of caves. An identification key of the species is given. Totally, 13 new taxa are described: Eustra hammondi n. sp., E. gomyi n. sp., E. matanga darlingtoni n. ssp., E. matanga negrosensis n. ssp., E. csikii burmanensis n. ssp., E. taiwanica n. sp., E. pseudomatanga n. sp., E. pseudomatanga cavernicola n. ssp., E. plagiata peguensis n. ssp., E. ceylanica n. sp., E. indica n. sp., E. storki n. sp., and E. andrewesiana n. sp. The genus Ozaenaphaenops Deuve, 1986, proposed for the troglobiomorphic species, is here considered as a junior subjective synonym of Eustra Schmidt-Goebel, 1846. A lectotype is designated for E. plagiata Schmidt-Goebel, 1846, E. japonica Bates, 1892, and E. batesi Lewis, 1896.
Insecta, Coleoptera, Adephaga, Paussidae, Ozaeninae, Eustrini, Eustra, Ozaenaphaenops, biospeleology, tropical caves, neoteny, Southeast Asia, India, Sri Lanka, Burma, Thailand, Malaysia, Laos, Vietnam, China, Japan, Philippines, Sulawesi, Indonesia, new species, new subspecies.