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The Hawaiian sandburrowers Crystallodytes cookei and Limnichthys nitidus were found to be protandrous hermaphrodites based on a histological examination of gonad morphology and development. The majority of individuals of both species (71% and 75%, respectively) had delimited ovotestes in which ovarian and testicular tissue were divided by a connective tissue barrier. In juveniles and functional males, the ovarian and testicular regions were similar in cross-sectional area, whereas in functional females, the testicular portion was absent or greatly reduced. Reproductive females were significantly larger in body size than functional males but did not differ significantly in size with transitionals (individuals which contained both developing ova and visible spermatozoa). The complete absence of functional females at the smallest size ranges suggests that both species are monogynic; all females are derived from previously mature males. The ovotestis morphology and sequence of gonad development present in C. cookei and L. nitidus are most similar to protandrous porgies (family Sparidae). When compared to sex changing species of the closely related genus Trichonotus (family Trichonotidae), the distinct ovotestis morphology (delimited in creediids vs. mixed in Trichonotus) and differing direction of sex change (protandry vs. protogyny) suggest that sex change evolved independently in these taxa. [ABSTRACT FROM AUTHOR]