![]() ![]() Two exceptional orders, Amphilinidea and Gyrocotylidea, inhabit the coelomic cavity of fishes and freshwater turtles, lack a divided body, and at least the first has members that possess a proboscis ( Gibson, 1994a, 1994b) these were previously grouped into a subclass called Cestodaria, but no molecular support was found for their monophyly ( Caira et al., 2017) in contrast, the remaining 17 orders were traditionally grouped in a subclass called Eucestoda these conform to what is the norm for the class, the monophyly of which is supported by molecular evidence ( Caira et al., 2017). Their life cycles are mostly indirect, requiring an intermediate and a definitive host in most of the cases, but sometimes more than 1 intermediate host is required to complete the cycle very rarely (as in Nematotaeniidae), the life cycle is direct, and an intermediate host is not required ( Schmidt, 1970 Lamothe-Argumedo, 1983 Caira et al., 2017). In their adult forms, tapeworms are endoparasites that typically inhabit the small intestines of vertebrates. This class consists of 19 recognized orders ( Caira et al., 2017). The members of the class Cestoda (sometimes spelled Cestoidea) are commonly known as tapeworms or cestodes and are distinguished from those parasitic flatworms in the classes Monogenea and Trematoda by their lack of a true gut, and by their mostly long and vermiform bodies which are divided into a scolex (the “head”), a neck region (the germinating zone), and a strobila (the “body”) formed by several proglottids in multiple stages of maturation (not to be confused with true segmentation, as seen in Annelida or Arthropoda Schmidt, 1970 Lamothe-Argumedo, 1983).
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