Favoritos de easy_to_distinguish

Was found parasitized in the anterior girdle of Placiphorella stimpsoni. In its mantle cavity groove over the head. Most of the shell was imbedded when it was alive, I dug it out just for identification and saving images. 3 Placiphorella stimpsoni were found being parasitized by Musculus cupreus in the total 13 individuals. The other two also parasitized in the anterior girdle.
Musculus cupreus is generally considered has hemiparasitism. Although some documents describe it as burrowing-living. I've seen the same situation happens on Styela clava and Phlebobranchia sp., and sometimes has a very high density:
https://www.inaturalist.org/observations/126602879
https://www.inaturalist.org/observations/239621502