Adult Eucestoda have a white-opaque dorso-ventrally flattened appearance, and are elongated, ranging in length from a few millimeters (about ¼") to 25 meters (80').

Most except caryophyllideans consist of a few to 4000 proglottids (segments) that show a characteristic body differentiation pattern into scolex (head), neck, and strobila.

[2] The scolex, located at the anterior end, is a small (usually less than 1 mm) holdfast organ with specific systems for fastening itself to materials: rostrum, acetabula, suckers, bothria, grooves, and hooks.

Members of the Eucestoda have no mouth or digestive tract, and instead absorb nutrients through a layer of microtriches over the tegument at the shared body wall surface.

[3] In addition to the body wall, several other systems are common to the whole length of the tapeworm, including excretory canals, nerve fibers, and longitudinal muscles.

[5] When a gravid proglottid that is distended with an embryo reaches the end of the strobila, it detaches and passes out of the host intact with feces,[4] with or without some tissue degeneration.

[4] After the scolex has differentiated and matured in the larval stage, growth will stop until a vertebrate eats the intermediate host, and then the strobila develops.

[9][10] Infection occurs through swallowing or antiperistaltic contractions during regurgitation carrying eggs or gravid proglottids to the stomach.

At this point, larvae hatch when exposed to enzymes and penetrate the intestinal wall, travelling through the body through blood vessels to tissues like the brain, the eye, muscles, and the nervous system (called neurocysticercosis).

[5] At these sites, the parasites lodge and form cysts, a condition called cysticercosis, producing inflammatory reactions and clinical issues when they die, sometimes causing serious or fatal damage.

[12] Eggs hatch in the gastrointestinal tract after the consumption of contaminated food, after which the larvae travel to the liver through portal circulation.

[5] When a larva becomes established in tissue, it develops into a "bladderworm" or "hydatid" and can cause various cancer-like cysts that may rupture and interact with nearby organs.

Most cases are asymptomatic, and the mortality rate is low, but various complications from these interactions may lead to debilitating illness.

Humans become infected by eating raw, undercooked, or marinated fish acting as a second intermediate or paratenic host harboring metacestodes or plerocercoid larvae.

[14] Clinical symptoms are due to the large size of the tapeworm, which often reaches a length exceeding 15 m (49 ft).

The evolutionary history of the Eucestoda has been studied using ribosomal RNA, mitochondrial and other DNA, and morphological analysis and continues to be revised.