Tetragonoporus calyptocephalus, formerly known as Polygonoporus giganticus, is a giant tapeworm that lives deep within the intestines of whales.
Many species of tapeworms reach impressive sizes, but the length of 40 meters of T. calyptocephalus makes it the longest parasitic worm on the planet, according to IFL Science. The most common tapeworm species affecting humans are typically found in the tissues of pigs, cattle, and salmon. In humans, the longest tapeworm species cannot match the size of T. calyptocephalus, although some still possess impressive lengths.
Whale tapeworms can reach up to 40m. (Photo: Funnyjunk).
A prominent example can be found at the Meguro Parasitological Museum in Tokyo, which displays a specimen of fish tapeworm (Dibothriocephalus nihonkaiensis) measuring 8.8 meters. This is one of the rare specimens of a giant tapeworm taken intact from a human intestine. However, they can grow much larger. According to a 2009 article, fish tapeworms can measure between 2 to 15 meters. The maximum size ever recorded for this species is 25 meters.
Researchers indicate that tapeworms have been parasitizing intestines for at least 99 million years, based on a unique amber fossil described in March 2024. This marks the first time human researchers have discovered a part of their body in fossilized form. Previously, all that had been collected were tapeworm eggs from Permian shark feces.
“Fossil data for tapeworms is extremely scarce due to their soft tissues and habitat within a host,” said Bo Wang, the lead researcher from the Nanjing Institute of Geology and Palaeontology. “This limits our understanding of their early evolutionary processes.”
Tapeworms are highly successful parasites that infect everything from birds to bears. However, in terms of length, few species can surpass tapeworms. They do not start off at a large size. The head of T. calyptocephalus attaches firmly to the intestines of the whale, and they gradually increase in length as new segments develop. The largest individuals can have up to 45,000 segments with fully developed testes and ovaries.
