D. molle is a species of tunicate, a colonial ascidian in the family Didemnidae. They feed on suspended plankton and detritus, and grow to a length of about 3cm. These urn-shaped tunicates have numerous and minute oral siphons -- not to be confused with a highly similar-looking species, Atriolum robustum, which has bigger oral siphons. This species varies in color: from white, orange to bright green. The green color inside is the result of being inhabited by minute blue/green algae.
Found in groups in shallow, sheltered water growing on dead coral, at depths of up to 146m. Distribution: Indian Ocean, Indo-West Pacific, Tanzania.
The first two photos show a group of tunicates -- I thought of "boy band" when I spotted them. The next two photos are of a larger, more fully-grown individual, spotted at a different time and location.