One of our readers recently sent us a photograph that was taken at the bank of a river at Falls Park in Sioux Falls, South Dakota. His initial thought was that the specimen was some sort of leech, but he questioned this thought because of the bizarre coloring of the creature in question. The specimen appears to be a few inches long with a flat body. It has tapered ends, and is shaped like a leaf. The specimen is black with light brown markings. We have two ideas as to what this creature is. We will explore both options below. Here is the photograph he included in his message:

Our first idea is that our reader’s initial thought was spot on, this could be a leech! Leeches are wide, flat, segmented Annelids that have suction cup-like appendages at each end of their bodies. While some leeches are only a few millimeters long, some grow up to 10 inches! They are often black, brown, or green, and sometimes have spots, stripes, or other markings. Most leeches live in shallow, slow-moving freshwater. There are around 1,000 species of leeches around the world!

Our next idea is that this mysterious creature is a freshwater flatworm. These flatworms belong to a larger phylum of flatworms known as Platyhelminthes. While many of the other flatworms in this phylum are internal parasites, freshwater flatworms are predators and scavengers of other soft-bodied invertebrates. Species of flatworms exist in most aquatic habitats, but freshwater flatworms are most commonly discovered on the surfaces and undersides of rocks in slow moving water.

In conclusion, a reader sent us a picture of a worm-like organism he found on a river bank. The creature has a wide, flat body with black and brown markings. We believe the specimen is either a leech or a flatworm!