Suborder : PLAKOBRANCHACEA
Superfamily : PLAKOBRANCHOIDEA
Very characteristic colour pattern, with a dark, almost black, background, fine white longitudinal lines and the foot, head and rhinophores edged with bright orange. In some specimens the parapodia can also be bordered with bright orange and in some specimens elongate white or bright blue spots are present along the outside of the parapodia just down from the edge. Thuridilla bayeri is clearly a synonym and so is T. ratna.
Described by Risbec as having 8 rows of white streaks down the parapodia, which are bordered with orange. He also describes a whitish T-shaped mark on the head between the rhinophores. Gosliner (1995) discusses the synonymy of T. bayeri and T. ratna but considers that the original description of Risbec’s Elysia gracilis is insufficient to allow an accurate identification.