Most nudibranchs crawl. Hexabranchus sanguineus, when disturbed, lifts the flared margins of its mantle and beats them in a travelling wave, moving through open water in a motion that gave it its common name. Swimming is an escape response rather than routine locomotion.
The animal feeds on sponges and sequesters macrolide compounds from them. Rather than merely storing these in its own tissues, it concentrates related compounds into the pink, ribbon-like egg masses it deposits on the reef, which are conspicuous and immobile and would otherwise be easy grazing. Chemically defended eggs allow the parent to leave them exposed.
A caution about the striking colour. Red appears black at depth, since red light is absorbed first, so the vivid appearance familiar from dive lights is not what a reef predator sees in ambient light. Whether the colouration functions as aposematic warning, as camouflage at depth, or as neither is not settled, and the chemical defence works regardless of whether the warning is seen.