Features: 8-10cm long, the worm can be as large as the palm of our hand! Body generally dark on the upperside (black to brown) with lots of little bumps that are yellow or orange tipped, as well as larger white spots. Seen from the top, it has a bluish white margin, while from the bottom it has a dark broad margin against a pale foot. It has a pair of small, erect and pointed, ear-like pseudotentacles at the front, made up of folded edges of the body.
The flatworm can be quite active, especially at night. Like a stealthy spotted mat, it is often seen gliding rapidly, hugging the surface closely, ruffling the body edges as it moves. One was even swimming from one seagrass blade to another, elegantly ruffling its body edges to 'fly' through the water. Sometimes, you might come across what appears to be a very large spotted black flatworm. Look closely and it will may turn out to be two such flatworms!
Similar animals: Acanthozoon species look very much like Thysanozoon species. They are only positively identified by microscopic examination: Acanthozoon has only one male pore while Thysanozoon has two.
Text source: Wild Singapur.com