Anisakids are nematodes (round worms) in the family Anisakidae. The main anisakids affecting humans are Anisakis species (including Anisakis simplex), Pseudoterranova species (including Pseudoterranova decipiens), and Contracecum species. In nature, they are parasites of fish and marine mammals; however, when ingested by humans, they cause a condition called anisakiasis. Humans become infected when ingesting live larvae in raw or undercooked fish. Once ingested, the larvae are unable to mature into adults, but may cause symptoms in a variety of manners; they may be 'coughed' or vomited up, or may cause gastric or intestinal pain by burrowing into the stomach or intestinal mucosa respectively. Rarely, they may penetrate the mucosa and enter the peritoneal cavity. Some individuals also develop an allergic reaction to anisakids and are therefore at risk for future reactions, even when dead worms are ingested. Anisakids are commonly found in a variety of fish including salmon and cod. Therefore, they are easily acquired for teaching purposes and very popular in medical school and global health labs! Shown here are a variety of photos of anisakids in fish - discovered in both food designed for consumption and specimens obtained for teaching. Click HERE for a (somewhat disturbing) video of a live anisakid discovered in a salmon dish. Anisakids resemble immature Ascaris lumbricoides but can be differentiated by the presence of a posterior spicule called a mucron. Presence and characteristics of a cecum can be used to differentiate the various anisakids commonly found in humans.