Convolutriloba retrogemma

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.

C. retrogemma, like many other acoels, contains dangerous toxins to keep it predators away, and, on death, it can release these toxins. This is harmful to nearby life such as coral and fish, and even people if infected fish are consumed.