Abstract
Glossiphoniidae is a family of freshwater leeches, notable for their unique behaviour of parental care. After hatching, juveniles remain on the ventral side of their parent, where they receive protection and grow until they are ready to depart from the parent leech. The detachment of juveniles is a crucial stage for their development and independence from their parents, potentially influenced by various factors. To investigate these factors, ten parental individuals of Orientobdelloides siamensis were studied in the laboratory. Three to five days after copulation, all parental leeches deposited approximately 361.6±37.79 eggs on the substrate, which were covered until the end of the brooding period. Incubation of their single-egg cocoons took 7-9 days. Subsequently, the newborns attached to the ventral annulus of the parent by their caudal sucker. Seven to eleven days after hatching, the caudal sucker of juveniles expanded over the parent's annulus, indicating readiness to depart. The young leeches detached from the parental venter, moved to the substrate, and continued living under the ventral side of their parent. Finally, to determine the timing of juvenile detachment, the space availability beneath the parental venter and yolk depletion after hatching were analyzed. By observing morphological characteristics and behaviors, this study was able to investigate the interaction between these factors, and their correlation with juvenile detachment in O. siamensis.