Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed into the environment to infect other organisms.

The adult tapeworm has a scolex (head), a short neck, and a strobila (segmented body) formed of proglottids.

Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork (Taenia solium), beef (T. saginata), and fish (Diphyllobothrium), or if they live in, or eat food prepared in, conditions of poor hygiene (Hymenolepis or Echinococcus species).

[5] Cestodes have no gut or mouth[6] and absorb nutrients from the host's alimentary tract through their specialised neodermal cuticle, or tegument,[7] through which gas exchange also takes place.

[8] Once anchored to the host's intestinal wall, tapeworms absorb nutrients through their surface as their food flows past them.

The sum of the proglottids is called a strobila, which is thin and resembles a strip of tape; from this is derived the common name "tapeworm".

[16][17] Though they are sexually hermaphroditic and cross-fertilization is the norm, self-fertilization sometimes occurs and makes possible the reproduction of a worm when it is the only individual in its host's gut.

All but amphilinids and gyrocotylids (which burrow through the gut or body wall to reach the coelom[6]) are intestinal, though some life cycle stages rest in muscle or other tissues.

In contrast, in the terrestrial Cyclophyllidea, proglottids are released steadily over a period of years, or as long as their host lives (iteroparity).

Proglottids leave the body through the anus and fall to the ground, where they may be eaten with grass by a grazing animal such as a cow.

This animal then becomes an intermediate host, the oncosphere boring through the gut wall and migrating to another part of the body such as the muscle.

After ingestion by a suitable freshwater crustacean such as a copepod, the first intermediate host, they develop into procercoid larvae.

Host antibodies can kill or limit cestode infection by damaging their digestive enzymes, which reduces their ability to feed and therefore to grow and to reproduce; by binding to their bodies; and by neutralising toxins that they produce.

[1][27] The fossil Rugosusivitta, which was found in China at base of the Cambrian deposits in Yunnan[28] just above the Ediacaran-Cambrian border, has great similarities to present day Cestodians.

The position of the Cestoda within the Platyhelminthes and other Spiralian phyla based on genomic analysis is shown in the phylogenetic tree.

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

Bodily symptoms which are sometimes present include abdominal pain, nausea, diarrhea, increased appetite and weight loss.

[36] There are several classes of anthelminthic drugs, some effective against many kinds of parasite, others more specific; these can be used both preventatively[37] and to treat infections.

[36] In Ancient Greece, the comic playwright Aristophanes and philosopher Aristotle described the lumps that form during cysticercosis as "hailstones".

[40] In Medieval times, in The Canon of Medicine, completed in 1025, the Persian physician Avicenna recorded parasites including tapeworms.

[40] In the Early Modern period, Francesco Redi described and illustrated many parasites, and was the first to identify the cysts of Echinococcus granulosus seen in dogs and sheep as parasitic in origin; a century later, in 1760, Peter Simon Pallas correctly suggested that these were the larvae of tapeworms.

[35] Mira Grant's 2013 novel Parasite envisages a world where people's immune systems are maintained by genetically engineered tapeworms.

[43] A full-page coloured image, purportedly from a women's magazine of that period, reads "Fat: the enemy ... that is banished!

"[35] When television presenter Michael Mosley deliberately infected himself with tapeworms he gained weight due to increased appetite.