Observations are reported for Dysidea avara sponges where once functioning oscula ( outlets) are converted through internal re-plumbing into functioning oversized ostia ( OSO; inlets). Flow tank studies employed high-speed photography and particle tracking of laser-illuminated 0.5 - 6.0 mu m diameter glass beads to trace particles streaming into OSO. A fluorescein dye/glass bead uptake experiment showed that an oversized ostium was connected through internal structures to the lone osculum. Beginning 30 s after uptake and continuing over a 20 min period, dye streamed from the osculum, but no beads emerged. Scanning electron microscopy revealed that beads were deposited only on the inhalant side of particle filtering choanocyte chambers and not on the exhalant side, suggesting that internal re-plumbing had occurred. Functioning OSO were also found on freshly collected specimens in the field, making it highly unlikely that formation of OSO was only an artefact of sponges being held in a laboratory tank.