In 2009, sanitation workers running a camera through a private sewage system came across a colony of strange, red blobs that throbbed and shuddered like living things. Video of the sewer things got pretty huge on Youtube, with all the usual wild guessing.
So what were these things, exactly? It turns out they were nothing more than colonies of Tubifex worms. These worms normally live in sediment at the bottoms of lakes or, as happened here, in sewers. Since there was no soil for the worms to burrow into, they were simply coiled around each other, forming the odd, lumpy balls. When the hot camera lights got too close, the worms would collectively retract, creating the illusion of a single large moving being. Apparently these colonies are fairly well known to sewer workers, who have given themt he delightful nickname "ass urchins".
Tubifex are pretty interesting animals. They're annelids, a large, successful group that includes earthworms and leeches. Tubifex often live in polluted, or low-oxygen sediments-- such as the aforementioned lake bottoms and sewers. To get oxygen in such inhospitable environments, they have tons of hemoglobin in their bodies, which gives them their bright red color. You can learn everything you'd ever want to know about Tubifex worms here.
For this drawing, I added a couple of large "queen tubifex" heads coming out of the mound like hydra heads. There's no report of the ass urchins sprouting giant heads, but then again there aren't any reports that say they DON'T sprout giant heads. Besides, how could I not include a depiction of a tubifex's adorably doofy face