Look at the horns first. Every aeolid has a pair of rhinophores standing up at the front end; on this genus they are strung with two or three swellings along their length, like beads on a cord. Nothing else on the reef has them, and once you know the shape you can name the animal from a bad photograph.
What it does is stranger than what it looks like. It eats eggs. Sea slugs lay their spawn in coiled ribbons stuck to rock, sponge or algae, thousands of embryos in a jelly rope left out in the open with no parent anywhere near it, and this species specializes in exactly that. Ribbons of other nudibranchs, ribbons of sea hares: a fixed, defenseless package of yolk that never has to be chased.
That gives divers the most reliable search method in this whole section. You do not look for the slug. You look for spawn, and then you look at the spawn closely, because a two-centimeter (0.8 in) animal sitting on a white coil is easy to walk straight past.
The diet shows on the outside. The color of the cerata on its back tracks the color of the eggs it has been working through, so the same species can be seen pale, orange or pinkish depending on whose nursery it found. It also explains what this animal does not have. Its relatives eat hydroids and anemones and keep the stinging cells from their prey as stolen weapons at the tips of the cerata. An egg ribbon carries no stinging cells. This one eats well and comes away unarmed.
- rhinophores carry two or three bulbous swellings along their length, which no other slug here has
- small, slim, with opaque white markings on the back and along the cerata
- cerata color varies between individuals depending on what they have been eating
- found sitting on a coiled egg mass rather than on a sponge or coral
