is a semi-transparent nudibranch growing to at least 7.5 cm. The body is oval and flattened. There are numerous swollen cerata, each with a central thin dark thread of digestive gland. The cerata tips contain an irridescent bluish-white pigment. Similar patches of pigment are found on the back, between the cerata and in the head region. The lamellate rhinophores are especially large and conspicuous, non-retractile and without sheaths. A coarsely ridged, sensory cocks comb-like structure called a caruncle lies between the rhinophores, which is unique to Janolus
species.Spawning has been recorded from April to September and in December (Thompson & Brown, 1984). The egg-mass contains a series of bead-like white or pale pink ovoids, each being a capsule containing up tp 250 separate individual spherical eggs (ova). The spawn is wound in a wavy circle pattern (Thompson & Brown, 1984).