07/21/2026
Freshwater sponges? You betcha. This one (photographed yesterday) flourishes in a cool, clear, highly oxygenated stream near where Debbie and I live. Its location will remain a secret because these colonies are all too prone to disturbance. Slosh around in a stream, and you kill them without meaning to. Even a light touch may damage them severely or wipe out an entire colony.
Sponges belong to the animal order Porifera. The name refers to the group's abundance of holes, or pores, through which these colonies of tiny organisms filter food out of their home waters. This particular colony, which Debbie spied first, occupies a patch of rock roughly the size of a half-dollar coin.
Some freshwater sponges, like this one, live where sunlight hardly ever strikes them. This sponge may well belong to the shade-favoring species Spongilla fragilis, but that's not much more than a guess. The resource that informs my casual spongology is Ann Haven Morgan's classic Field Book of Ponds and Streams, published in 1930. One must devote a large portion of one's life to the study of sponges to gain much mastery of them, and I confess I am too much of a generalist. Other freshwater sponge colonies, sometimes in the same stream, glow a brilliant green. These harbor chlorophyll-carrying cells called zoochlorellae inside their own cells. Amazing!