Tenias, also known as tapeworms, are flat, segmented worms that live in the intestines of various animals, including humans. They belong to the class Cestoda and can grow to significant lengths, sometimes reaching several meters. These parasites attach themselves to the intestinal wall using specialized structures called scolex. Infection typically occurs through the consumption of undercooked meat or contaminated food and water. Symptoms may include abdominal pain, nausea, and weight loss, but some individuals may remain asymptomatic. Treatment usually involves medication that targets the worms, helping to eliminate them from the body.