Thysanozoon nigropapillosum Swims & Dazzles

Thysanozoon nigropapillosum is a dazzling flatworm. Yellow- or gold-tipped papillae cover its black body. Its body margin has bold white edges.

Many Confusing Names

Thysanozoon nigropapillosum lacks a standard English name. Some call it the Yellowspotted, Yellow-spotted, Yellow Spot, or Yellow-speckled Flatworm. Others refer to the spots as gold. Some online sources call it the Galaxy Flatworm since its body looks like a maze of stars.

Appearances of Thysanozoon nigropapillosum in Gorontalo

Before opening diving in Gorontalo, Miguel’s Diving surveyed potential dive spots. In May 2000, we recorded our first sighting of Thysanozoon nigropapillosum off the coast of Bone Pantai Regency. Since then, we have rarely encountered this beautiful flatworm—perhaps only once every five years!

In 2025, one of our guests captured Thysanozoon nigropapillosum on video, creating an intriguing clip. Flatworms can swim short distances by waving their flat bodies. The video shot by Rainer de Reuter captures this undulating motion perfectly!

Notice the two white-tipped protrusions at the front of the flatworm. These are pseudotentacles. They sense light and motion, helping the flatworm navigate.

Favorite Food

Thysanozoon nigropapillosum feeds on certain species of tunicates. One of its favorites is Didemnum molle, which is very common in Gorontalo. The flatworm engulfs the tunicate’s thin body with its mouth. However, it does not digest the hard calcium spicules that give the tunicate structure. Instead, these are expelled as pellets.

Savage Mating

All flatworms are hermaphrodites, meaning they have both male and female reproductive organs. Thysanozoon nigropapillosum also has two penises. During mating, each flatworm attempts to inseminate the other. First, special structures called rhabdites grip the partner’s edge, providing a strong hold even while swimming. Then, the two try to stab each other with a penis—or both! The maze of yellow papillae makes aiming difficult, and missed attempts often result in dermal impregnation.

Where to Find this Dazzling Flatworm

Found throughout Indo-Pacific waters, this dazzling flatworm can grow up to 8 centimeters long. Divers can spot it at depths ranging from one to twenty meters.

For your chance to see unusual marine life in Gorontalo, please make your dive reservations directly with Miguel’s Diving.