Invertebrates
Tapeworm
Cestoda · also called tapeworms
Inside the intestine of its host, a tapeworm has no mouth to feed with and no gut to digest anything, yet it grows steadily longer regardless, absorbing everything it needs directly through its own skin from food its host has already broken down.
Overview
The tapeworm, class Cestoda, is a parasitic flatworm found wherever suitable host animals live across nearly every habitat worldwide. Its complete lack of a digestive system, combined with a body built from an ever-growing chain of self-contained reproductive segments, makes it one of the more anatomically stripped-down and specialised animals known.
An animal that gave up digesting its own food
Having evolved to live permanently surrounded by pre-digested nutrients inside a host’s gut, the tapeworm simply discarded the mouth and digestive system most animals consider essential, absorbing everything it needs directly instead.
Status
Not Evaluated — population levels are tied directly to host animal populations rather than independent habitat availability.
Tapeworm: common questions
How does a tapeworm eat if it has no mouth?
A tapeworm has no mouth, gut, or digestive system of any kind, and instead absorbs already-digested nutrients directly through its outer body surface from the food its host has already broken down, an efficient strategy that works only because the parasite lives permanently bathed in nutrient-rich material inside the host's intestine.
What are the segments that make up a tapeworm's body?
A tapeworm's body consists of a long chain of repeating segments called proglottids, each one containing its own complete set of reproductive organs, with new segments continuously produced from the neck region just behind the head and older, more mature segments pushed further down the body over time.
Why do tapeworms need more than one host animal?
Most tapeworm species require at least two different host animals to complete their full life cycle, typically an intermediate host in which larval stages develop before an adult worm can mature within a separate final host, a multi-host strategy that has evolved across many different parasite lineages.
How does a tapeworm stay attached inside its host?
A tapeworm attaches firmly to the inner wall of its host's intestine using a specialised head structure called a scolex, which is typically equipped with hooks, suckers, or both, allowing the parasite to resist being dislodged by the ordinary movement of digested food passing through the gut.