Have you ever seen a swimming flatworm? These colorful animals can be found moving swiftly across the reef, but to catch one in open water is the real treat. Flatworms are soft-bodied invertebrates which propel themselves through the water with a mesmerizing wave of the body.
Last year while I was diving in Raja Ampat Indonesia I came across an elegant flatworm, and made sure to capture the moment. The Yellow-Spotted Flatworm (Thysanozoon nigropapillosum) is common throughout the indo-pacific and there are dozens of speckled, spotted, and striped species found in the waters around Indonesia.
I want you to try something. Run your tongue along the roof of your mouth. Can you feel small round bumps? These are called Papilla. The yellow spots on the back of the flatworm are raised above the body like papilla, which is where it get’s the common name yellow papillae flatworm.
This flatworm grows into a long oval shape and the yellow spotted flatworm can grow up to 3 in (76 mm) in length. Other species of flatworms can be less than a millimetre in size and sometimes hundreds of transparent flatworms can be found living and feeding on coral.
Flatworms have no body cavity and they have specialized circulatory and respiratory organs which restrict them to having a flattened shape that allow oxygen and nutrients to pass through their bodies by diffusion. Another interesting fact about flatworms is they are bilateral animals and have perfect symmetry on both sides of their body.