Encyclopedia

Ocellated Wart SlugPhyllidia Ocellata Warm orange-gold spreads across this chunky little nudibranch, broken by bold black rings that encircle raised white and yellow tubercles along its back. The bumps give its body an almost armored texture, while smaller spots gather toward the edges and the yellow rhinophores peek out from the front. It has a wonderfully odd combination of softness and structure, like a creature covered in tiny knobs that someone has carefully arranged into a pattern. Size: Up to around 70 mm Range: Indo-Pacific; from the Red Sea across the tropical Indian Ocean and Southeast Asia to the western...

Swallowtail Headshield SlugChelidonura Hirundinina Black makes everything else hit harder on this slug. Electric turquoise, vivid orange, yellow and crisp white streak across the body in fine, almost neon lines, with the colors becoming especially wild around the head and those long, split tail extensions. Some markings run cleanly from front to back, while others break into little flashes and spots, giving the whole animal an almost electric energy. Then there are those impossibly long tails, edged in bright color and trailing behind like ribbons. It is small, but visually it is absolutely outrageous. Size: Around 20–40 mm Range: Tropical...

Pink FlatwormProstheceraeus Roseus A vivid ribbon of rose and violet, this flatworm carries a series of fine white lines lengthwise across its body, with a crisp pale border tracing the entire edge. Two small magenta folds rise at the front like understated horns, while the softly rippled margins give the otherwise flat body a constant sense of movement. It glides over the reef with such effortless smoothness that, for a moment, it barely seems to touch the surface at all. Size: Up to around 30 mm Range: Mediterranean Sea and eastern Atlantic; from Portugal and Spain south to Senegal, including...

Striped PhyllidopsisPhyllidiopsis Xishaensis Four fine black lines run lengthwise across the pale blue-white body, following the low rows of rounded tubercles and giving this tiny nudibranch an unusually clean, linear look. The stripes are not perfectly uniform, which keeps the pattern from feeling rigid, while the pale body lets every dark line stand out clearly. Small, restrained and remarkably graphic, it looks almost as though someone drew four careful strokes along its back. Size: Up to around 20 mm Range: Western Indo-Pacific, from the Philippines and Indonesia to southern Japan and Australia Habitat / Depth: Tropical reefs and rocky substrates,...

Picasso TriggerfishRhinecanthus Aculeatus A sharp little reef character in mustard yellow, white, black and blue, the Picasso Triggerfish seems to have been assembled from bold shapes rather than painted in gradual shades. A dark band cuts across the eye, while pale blue lines curl around the face and a yellow patch runs along the snout. Behind the head, broad black markings break up the body into angular blocks, giving this chunky fish an unmistakably graphic personality. It looks permanently alert, as though it has somewhere important to be. Size: Up to around 30 cm Range: Indo-Pacific; from East Africa through...

Hammerhead Sea SlugChelidonura Varians Midnight blue gives this unusual sea slug a sleek, almost shadowy presence, broken by electric-blue lines that trace its body from head to tail. Its broad head spreads outward into two unmistakable lobes, while the long, tapering tails trail behind like twin ribbons. Built low to the sand and always moving with purpose, it has the look of a tiny underwater predator designed for hunting rather than hiding. Size: Up to around 70 mm Range: Tropical Indo-West Pacific; from the Red Sea and East Africa through the Indian Ocean and Southeast Asia to Japan, northern Australia...