So I've just returned from a month long collecting trip through California and Oregon. The weather did not always cooperate but collecting was still pretty awesome. The very first day of the trip, we stayed in a random campsite off the I-10 outside of Los Angeles in Cherry Valley. It was rainy and hailing and absolutely miserable but the Tenebs were still out. Found the usual California genera, Coniontis, Coelocnemis, Nyctoporis, but then my friend found something you don't see every day. While combing through a nest of Liometopum, he pulled out two of these guys.
This is Anchomma costatum. One of the few Tenebs in the US that has 4-4-4 tarsi instead of 5-5-4. It was originally described as a Colydiid, then placed with the Stenosini in Tenebrionidae, and now rests in Anepsiini. While it was found in an ant nest, it is probably not obligate upon the ant and instead, like many Tenebs, probably feeds on the ant's refuse.