Australian Blue Dragon

Overview

The Australian Blue Dragon (Pteraeolidia ianthina) is a distinctive nudibranch endemic to the coastal waters of southeastern Australia. Often referred to as a "blue dragon" due to its sinuous, dragon-like appearance, this sea slug is a common sight for divers in the region.

Appearance

This species features an elongated, slender body covered in clusters of finger-like projections called cerata. Its coloration is highly variable, ranging from translucent tan or white in juveniles to shades of brown, lavender, or deep blue in adults, depending on the presence of symbiotic algae. Key identification features include two purple bands on its long oral tentacles and lamellated rhinophores.

Biology & behavior

Pteraeolidia ianthina is a "solar-powered" nudibranch that maintains a symbiotic relationship with photosynthetic dinoflagellates (zooxanthellae) within its tissues. By farming these algae, the slug can supplement its nutrition with sugars produced through photosynthesis, allowing adults to survive for extended periods without traditional feeding. Notably, this is one of the few nudibranch species known to remain near and protect its egg masses after laying them.

Feeding

Adults primarily feed on hydroids, with the solitary hydroid Ralpharia being a preferred food source. Juveniles are typically white or pale because they have not yet acquired their initial population of symbiotic zooxanthellae, which they likely obtain by consuming specific hydroids early in life.