close up photo of a segmented worm's frontal end with a black backgroundFor High Country News, Carly Cassella (@carlycassella) introduces us to an ongoing research project aiming to solve the mystery of an unknown species of oyster-parasitizing mud worm that is showing up in Northwest oyster beds. Where did these worms come from, and what are they? Fortunately, scientists have a great source of clues: ancient oyster shells, which still bear, even half a billion years later, parasitic scars and chemical traces of their environments. Photo: Smithsonian Environmental Research Center via Wikimedia Commons