Convolutriloba retrogemma is a reddish-brown acoel 2 mm in length also commonly known as redbug, red planaria, rust flatworm, or simply red flatworm.

It is a marine animal that gets energy from its endosymbiotic algae or from the consumption of small invertebrates such as copepods and rotifers.

Like some other acoels, it is known to starve coral of sunlight while searching for food on the corals' surface due to its rapid reproduction.

Convolutriloba retrogemma reproduce quickly either sexually by laying eggs or asexually by using budding and binary fission, where it splits up and makes a bud that will create a new worm,[1] or by using fragmentation, where it forms new parent organisms from fragments of one original parent organism.

[2] Due to their reproduction techniques they can be a plague to aquariums and fish tanks, as they are very harmful, unsightly, and difficult to remove without harming other life nearby.