Cestoda

There are approximately 6,000 described species of tapeworms (or cestodes). As adults, they are obligate parasites in the gut of vertebrates. Interestingly, tapeworms lack all elements of the digestive system; they possess no mouth or gut of any sort! Instead, they rely on their hosts for nutrients, which they absorb through their body surfaces. In fact, tapeworms possess unique extensions of their body surface called microtriches, that, among other functions, are thought to aid in absorption of host nutrients. The body of a tapeworm consists of two main regions: an attachment region called a scolex that is often highly muscular an adorned with a variety of attachment structures such as hooks, tentacles, and suckers; and the ribbon-like body, called the strobila, that usually consists of a chain of proglottids that generally house a set of male and female reproductive organs. These hermaphroditic flatworms are egg-producing machines! They need to produce so many eggs because tapeworms have complex life cycle’s, often requiring a series of 3 or more hosts to reach adulthood in the digestive tract of their final vertebrate host. It is in this definitive host that tapeworms reach sexual maturity and reproduce.