A dark oval, brown through gray to nearly black, sprinkled with small white dots and outlined by a pale margin, up to 6 cm (2.4 in) long. In torchlight the dots read as a scatter of sparks against the dark ground, which is how the animal is picked out on a night dive long before its outline resolves.
Disturb one and it swims. The body lifts clear of the reef and travels in slow vertical undulations, the whole margin rippling like fabric in a draught, until it settles somewhere else. It is one of the strangest things to watch underwater, mostly because nothing about a flat brown sheet suggests it can do that.
The front edge carries a pair of small folds called pseudotentacles - not true tentacles, just raised flaps of the margin - which the worm holds up as it moves. They carry the sense organs that steer it toward food, and their shape is one of the details specialists use to tell one Pseudobiceros from another when the colors overlap.
- brown to near-black body sprinkled with small white dots
- pale or white margin outlining the whole animal
- up to 6 cm, oval, edges gently ruffled
- swims with whole-body undulations when lifted off the bottom
