Gold-dotted Flatworm

Overview

The Gold-dotted Flatworm (Thysanozoon nigropapillosum) is a striking marine invertebrate known for its deep black body and vibrant, yellow-tipped dorsal papillae. Often found in tropical reef environments, this flatworm is recognized for its graceful, undulating swimming motion and distinctively ruffled, opaque white margins.

Appearance

This species features a broad, flattened body that can reach up to 80 mm in length. Its dorsal surface is covered in numerous rounded papillae of varying sizes, each tipped with yellow or orange. The ventral side is typically dark brown. Near the anterior end, it possesses a pair of folded, ear-like pseudotentacles, and a horseshoe-shaped cluster of cerebral eyespots is located just behind them, though these are often obscured by the worm's dark coloration.

Distribution & habitat

The Gold-dotted Flatworm is widespread across the tropical Indo-Pacific, including the Red Sea and the Indian Ocean. It is commonly encountered in shallow sub-tidal zones, where it is often found crawling along the substrate of external coral reefs.

Biology & behavior

This flatworm is a simultaneous hermaphrodite. During mating, individuals engage in complex behaviors, including the use of a forked penis to grip a partner's body margin. Sperm transfer often occurs via dermal impregnation, a process where sperm is injected directly through the skin. When threatened or moving across open water, it propels itself using rhythmic, wave-like contractions of its body margins.

Feeding

As a carnivore, this species feeds primarily on tunicates. It uses its large, folded pharynx to engulf prey, such as Didemnum species, and later regurgitates indigestible food pellets containing the calcareous spicules found within the tunicates' tissues.