Leptecodon
Leptecodon (meaning "small tooth") is a genus of prehistoric mackerel-like ray-finned fish which was described by Williston in 1899 and was possibly preyed on by other sea creatures. However, it was a hunter of smaller creatures itself. This fish sometimes hid in clams such as "Inoceramus". The first-discovered fossil was inside a clam. Many believe that "Leptecodon" had formed a symbiotic relationship with the clam rather than get eaten by "Inoceramus". Another fish from the same time and place, "Caproberyx", has also been found among "Inoceramus.