Flatworms were the first animals to move in a direction of their choosing because they were the first animals to have heads! Having a head also makes them the first animals with bilateral symmetry. In addition to having heads, they were the first animals to have organs since they were the first animals with three tissue layers. Being small and flat allows these animals to have a larger surface area to volume ratio which allows for easy gas exchange from the environment to the animals internal cells.
Cephalization
When an animal has what we call a "head," It means that many of their sensory organs or nervous control is located at the anterior of their body. (remember anterior, antenna) In the case of flatworms, they have the first brain, called a cerebral ganglion, and nerve cords attached to it that stretch the length of their body and branch across to each other. For some flatworms, as long as the anterior portion of the worm is kept in tact, the rest of the body can repair itself. Sometimes, they can be cut directly down the center from anterior to posterior and two worms will regenerate. |
Free swimming
Free swimming marine and freshwater flatworms belong to the class Turbellaria. They can range in size from microscopic to about two feet! Most are hermaphroditic and reproduce sexually.
Free swimming marine and freshwater flatworms belong to the class Turbellaria. They can range in size from microscopic to about two feet! Most are hermaphroditic and reproduce sexually.
Parasitic Flukes
One parasitic class of flatworms are flukes of class Trematoda. Many of them have a parasitic life cycle that includes two hosts. There is one species that uses three hosts, ants, snails, and mammals.
One parasitic class of flatworms are flukes of class Trematoda. Many of them have a parasitic life cycle that includes two hosts. There is one species that uses three hosts, ants, snails, and mammals.
Parasitic Tapeworms
Tapeworms are parasites that belong to the class Cestoda. They are commonly found in adult vertebrate digestive tracts. Sections on the tapeworm containing eggs called proglottids break off and are excreted in waste.
Tapeworms are parasites that belong to the class Cestoda. They are commonly found in adult vertebrate digestive tracts. Sections on the tapeworm containing eggs called proglottids break off and are excreted in waste.