Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Platyhelminthes
Class Cestoda
Common name: tapeworms
Overview
Tapeworms are endoparasites of vertebrates, often using invertebrates as intermediate hosts. An anterior attachment organ with suckers or hooks, known as a scolex, allows the tapeworm to fasten to the digestive tract of the host. Adults are long and flat, with the largest species, Polygonoporus giganticus, growing to over 30 m inside the gut of whales. Most species are much smaller than this.
Distribution and diversity
Worlwide, there are several thousand species of tapeworm described. Approximately 500 species in 194 genera and 54 families are described from Australia.
Life cycle
Adult tapeworms are hermaphroditic, their bodies made up of numerous reproductive segments called proglottids. Proglottids containing eggs are detached from the rest of the tapeworm and pass out of the host with the faeces. The eggs then need to be ingested by an appropriate intermediate host in which the larvae hatch and begin to develop. If the intermediate host is eaten by a definitive host (the correct vertebrate species) the adult stage can develop.
Feeding
Tapeworms do not have a digestive system, feeding off of nutrients absorbed directly from the host.
Ecology
As cestodes have evolved to parasitise nearly every vertebrate species, their ecology is varied. As endoparasites, they are rarely seen in the mature form except when removed from the gut of an infected host.
