A copepod parasite on a hatchetfish, Gulf of Mexico.

This hatchetfish is having a bad day...more like a bad few weeks to months. The copepod parasite on the outside of this fish, an ectoparasite, has attached and used its mouth part to pierce the outer wall of the fish. That mouth part then wraps around the internal organs of the fish and specifically pierces the digestive tract - feeding on whatever the fish has fed on. To make matters worse, the mouth part is barbed...this parasite isn't coming off. The long pair of threads trailing from the parasite are egg sacs. Photographed in the Gulf of Mexico. This species photographed during the DEEPEND project (www.deependconsortium.org).