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Flatworm
© 2009 Daniel W. Reed
This little Flatworm is about 1cm long and lives in the freshwater of a small seasonal stream in a Cedar Glade. (The species may be Dugesia tigrina which is common in the U. S.) Flatworms are usually carnivores and most Flatworms are benthos which means they live in the benthic zone which is the lowest ecological region of a body of water and includes the sediment layer. Flatworms seem very simple animals having no heart, lungs or anus but the do have a brain and if you look closely at the photo you can see the ocelli or eye spots. Ocelli are sensitive to light but do not form images or even determine the direction of the light. Respiration is by diffusion through the surface of the body so they must be thin. The reproductive system is fairly complex as they are hermaphroditic but do copulate, however, they can also reproduce by division. They simply contract at the midpoint until they separate into two bodies. This asexual reproduction occurs at warmer temperatures (above 10 degrees C) while at cooler temperature they reproduce sexually. Many Flatworms can be cut into pieces and each piece will form a new Flatworm. Additionally the head may be split to produce a creature with multiple heads. There are thousands of different species of Flatworms ranging in size from less than 1mm long to over 50cm. Some species live in sea water, some in fresh water and a few live in moist terrestrial environments. Most are free swimming carnivores but some are parasitic.