Identification
*Chromodoris annae* is a masterpiece of the reef, reaching a modest but striking 5 cm in length. Its mantle is a luminous, electric blue, bisected by three bold, black longitudinal lines. A critical field mark for photographers: look for the "bridge" of blue between these black lines. The entire mantle is framed by a vibrant, continuous orange-to-yellow border. To distinguish it from the nearly identical *C. lochi*, check the perimeter; *C. lochi* typically lacks this solid orange edge, appearing more whitish-blue at the margins. Its perky, lamellate rhinophores (scent horns) and feathery branchial plume (gills) are a matching, vivid orange, providing a stunning contrast to the sapphire body.
Habitat & Range
This species is a jewel of the Indo-West Pacific, most commonly sighted within the "Coral Triangle"—specifically Indonesia, the Philippines, and Papua New Guinea. They are residents of lush tropical reefs, typically found on sheltered slopes and vertical drop-offs. While they can be found in the intertidal zone, they are most frequently spotted by divers at depths between 15 and 30 meters, often nestled under ledges or on sponge-encrusted rock faces.
Behaviour
Observing *C. annae* is an exercise in "slow-motion elegance." They glide over the substrate on a muscular foot, their rhinophores constantly twitching to "sniff" out chemical trails in the current. They are solitary but often found in high-density "hotspots." As simultaneous hermaphrodites, when two individuals meet, they engage in a reciprocal dance to exchange sperm. An observer might be lucky enough to find their egg mass: a delicate, rose-like spiral ribbon attached to the reef.
Diet
These nudibranchs are highly specialized carnivores, feeding almost exclusively on sponges of the genus *Spongia*. Using a specialized, sandpaper-like tongue called a radula, they scrape away at the sponge's tough surface to ingest the nutrient-rich tissue beneath.
Fascinating Fact
Their neon wardrobe isn't for vanity—it’s a "keep away" sign! This is called *aposematism*. By sequestering toxic chemical compounds from the sponges they eat and concentrating them in their own skin, *C. annae* becomes incredibly distasteful. Their bright colors serve as a vivid warning to hungry fish that one bite will result in a very bitter, potentially toxic mistake.