This Obscure Creature is No Thicker Than a Piece of Card Stock

Marine flatworms are among the ocean’s most unique, albeit strange, organisms. Their undulating movements make them look like silk sheets underwater. Marine flatworms are skittish but are not uncommon around coral reefs. Vibrant, bold hues like the Platyhelminthes in this video by @ocean.life.explorer are hard to miss, but what are they, exactly?

What is This Marine Flatworm Doing?

The most fascinating aspect of this video is that the flatworm isn’t doing anything spectacular. This ethereal nature is normal for a marine flatworm when swimming thanks to its underwater wings. Its thin body undulates in a wave-like movement that propels it forward. This displaces water around it, allowing it to move quickly and efficiently. Interestingly enough, this creature is as flat as it looks. Its thickness is not much more than a piece of cardstock, making it thin enough to squeeze through crevices and contort to fit tight spaces.

You can’t tell from this video, but a marine flatworm only has two openings: one for its mouth and one to excrete waste. Their bodies are made of soft tissue with no skeletal structure or hard membrane, making them extremely flexible. They do not require a respiratory system since their bodies diffuse oxygen from the surrounding ocean water.

Marine Flatworms in the Wild

This odd species is most commonly found near coral reefs. Here, they hunt for worms, crustaceans, fish, algae, and occasionally carrion. Coral reefs offer perfect camouflage and are convenient hiding spots. Divers often see them in tropical locations, where reefs are abundant. When threatened, the marine flatworm has an interesting defense mechanism. Some species, such as Planocera multitentaculata, are toxic. They’ve been found to contain tetrodotoxin, similar to the toxin in pufferfish.

Not every marine flatworm has this toxin, and some evade predators in other ways. Similar to other worms, the pieces of a marine flatworm will regenerate if they’re lost. This helps the species to escape close encounters without losing its life in the process. In moments of extreme stress, a flatworm’s body can sometimes break apart. Its regenerative abilities are so advanced that it can reform quite easily. Sometimes, a flatworm will reform into several new worms if there are enough pieces of its broken body.

Its Color Can Be a Warning

In nature, bright colors are often a warning to potential predators. The flatworm’s bright outer membranes can mean they’re toxic in the marine world. These bright colors warn any larger animal to avoid marking them as prey. Alternatively, some flatworms are colored similar to their environments. These species prefer to hide out and seek shelter among their surroundings. Their camouflage helps them evade large predators and allows them to blend in while they move among coral reefs.