Platyhelminthes (Flatworms and Tapeworms)

"Platyhelminthes (platy = flat and helminth = worm), or simply ‘flatworms’, are dorsoventrally flattened and bilaterally symmetrical worms (Figure 1A,B). Often speculated in the classic literature to represent primitive basal bilaterians, modern molecular phylogenetic analyses place the Platyhelminthes within the Lophotrochozoa, a clade of invertebrate animals that includes annelids (segmented worms) and mollusks. Free-living members of the phylum, the so-called turbellaria, are largely restricted to marine and freshwater environments; however, some taxa, such as land planarians (Figure 1B), are capable of inhabiting warm humid terrestrial habitats. Turbellarian flatworms are almost entirely carnivorous, scavenging on the remains of dead animals or in some cases tracking, capturing, and killing their prey. Although these free-living taxa have evolved to thrive in a variety of habitats worldwide, the most successful group of flatworms without question belong to the Neodermata. This group of obligate parasites includes both flukes and tapeworms that together are responsible for a significant disease burden in livestock and humans throughout the world.

Given the diversity of flatworms it is difficult to make sweeping generalizations that unite all members of the phylum. However, unlike most bilaterians, flatworms lack a coelom and possess a ‘blind gut’ where food enters and exits via the same orifice (that is to say, they have no anus). Flatworms are also dorsoventrally flattened, ensuring the diffusion of oxygen and nutrients to their tissues. Despite this constraint, the absence of a cuticle, exoskeleton or shell has allowed these soft-bodied worms to adopt a dizzying array of shapes, body plans and sizes (Figure 1B–O). Many free-living flatworms are microscopic, but some can reach >10 centimeters in length (for example, land planarians; Figure 1B). These variations in body sizes and shapes are even more exaggerated among members of the Neodermata. Indeed, larval Neodermata rarely resemble the adult parasite (Figure 2), and tapeworms, arguably the most notorious of all Neodermata, can reach tens of meters in length growing inside their hosts (Figure 1K,L)."

Source: Colins, James J., III. (2017). Platyhelminthes. Current Biology 27(7): R252-R256. https://doi.org/10.1016/j.cub.2017.02.016

Class: Cestoda

Order: Onchoproteocephalidea

Family: Onchobothriidae

Class: Rhabditophora

Order: Fecampiida

Family: Fecampiidae

Order: Proseriata

Family: Otoplanidae

Order: Tricladida

Family: Cercyridae

Family: Dugesiidae

Family: Geoplanidae

Family: Kenkiidae

Class: Trematoda

Order: Stichocotylida

Family: Stichocotylidae

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