share the common features of all nematodes: the vermiform body plan, round in cross section, and a lack of segmentation. The body cavity is reduced to a narrow pseudocoel. The mouth is located anteriorly and surrounded by projections used in feeding and sensation, with the anus slightly offset from the posterior. The squamous epithelium secretes a layered cuticle to protect the body from digestive acids. As with all parasites with a complex life cycle involving a number of hosts, details of the morphology vary depending on the host and life cycle stage. In the stage which infects fish, Anisakis species are found in a distinctive "watch-spring coil" shape. They are roughly 2 cm long when uncoiled. When in the final host, anisakids are longer, thicker, and more sturdy, to deal with the hazardous environment of a mammalian gut. Health implications Anisakids pose a risk to human health through intestinal infection with worms from the eating of underprocessed fish, and through allergic reactions to chemicals left by the worms in fish flesh. Anisakiasis Anisakiasis is a human parasitic infection of the gastrointestinal tract caused by the consumption of raw or undercooked seafood containing larvae of the nematode Anisakis simplex. The first case of human infection by a member of the family Anisakidae was reported in the Netherlands by Van Thiel, who described the presence of a marine nematode in a patient suffering from acute abdominal pain. It is frequently reported in areas of the world where fish is consumed raw, lightly pickled, or salted. The areas of highest prevalence are Scandinavia (from cod livers), Japan (after eating sashimi), the Netherlands (by eating infected fermented herrings (maatjes)), Spain (from eating anchovies and other fish marinated in escabeche), and along the Pacific coast of South America (from eating ceviche). The frequency in the United States is unknown, because the disease is not reportable and can go undetected or be mistaken for other illnesses. Anisakiasis was first recognized in the 1960s. During the 1970s, about 10 cases per year were reported in the literature. The frequency is probably much higher, due to home preparation of raw or undercooked fish dishes. In Japan, more than 1,000 cases are reported annually. Development of better diagnostic tools and greater awareness has led to more frequent reporting of anisakiasis. Within a few hours of ingestion, the parasitic worm tries to burrow though the intestinal wall, but since it