Phylum Platyhelminthes:
Like acoelomorphs, members of the phylum Platyhelminthes are dorsoventrally flattened and so are commonly called “flatworms.” In fact, that’s what “platyhelminthes”
means – “platy” means “flat” and “helminthes” means “worms.”
To say that an animal’s body is
dorsoventrally flattened means that it is compressed from the top and bottom, not from the sides; in other words, it’s wider than it is tall. A
laterally-compressed animal, in contrast, is taller than it is wide.
As you might imagine, acoelomorphs and platyhelminths have a great deal in common. In fact, acoelomorphs were originally classified as members of the Platyhelminthes, before it was discovered that they have a number of important molecular and developmental dissimilarities.
Platyhelminths range from only a millimeter or so in length up to 10 meters or more in length for some tapeworms. Most are only a few centimeters in length, however. Many species are free-living, but quite a lot of modern species are highly-specialized parasites, and these are the ones most people think of when they think of platyhelminths.
“What is a ‘parasite’?” I hear you ask. Well, a
parasite is an organism that lives on or inside another organism (called the
host) and feeds on its host’s tissues. A
free-living organism is one that does
not live on or inside another organism.
Phylum Platyhelminthes
What are the symptoms of a liver fluke infection? I like sushi and has eaten plenty in my life. They were cooked though, or so I thought.
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