ABSTRACT
The term “helminth” (plural, helminthes) is commonly used to describe various organisms belonging to the phylum Platyhelminthes (fl ukes, tapeworms, and other fl atworms) and the now-obsolete phylum Nemathelminthes (roundworms and their relatives) [1]. Platyhelminthes is one of the acoelomate phyla and includes several important classes, such as Cestoda and Trematoda. Nemathelminthes
(or Aschelminthes) was formerly considered a phylum to represent the pseudocoelomate organisms. It is now obsolete and divided into several distinct phyla, such as Nematoda, Nematomorpha, Acanthocephala, Entoprocta, Rotifera, Gastrotricha, Kinorhyncha, etc. Among these, Nematoda (roundworms), Nematomorpha (horsehair worms), and Acanthocephala (thorny-headed worms) are important. In recognition of recent proposals based on molecular phylogenetic analysis, taxonomical status of these phyla is rapidly altered. In this chapter, the more traditional and common classifi cation is embraced. The Annelida (earthworms, leeches) are not regarded as helminthes, though some (e.g., leeches) may be parasitic and others (e.g., earthworms) may serve as intermediate hosts of helminthes [1,2].
