The Conchological Society of Great Britain and Ireland

                                                                                       Updated August 2012

synonym: Flabellina lineata (Lovén, 1846) accepted by WoRMS.

Body (excluding appendages)
Usually up to 30 mm long, occasionally 50mm. Translucent white with, usually near-continuous, opaque white dorsal line from in front of rhinophores to posterior group of cerata [image1], and a similar line on each side from the anterior group of cerata to the tip of the tail [2], the two lateral lines uniting on the tail to make a doubly thick line. Viscera visible in anterior half of translucent body, and white ovotestis lobules visible in the posterior of mature specimens [1]. Posterior half of juveniles, under circa 9 mm, lack ovotestis so substrate visible through body [4].
Cerata
Cerata usually held so dorsum of body visible. Arranged in 5 – 8 groups on dorso-lateral ridge on each side of body [5]. Translucent white revealing orange, red or reddish brown internal digestive gland and white cnidosac at tip. Anterior and posterior white pigment lines, or series of marks, rise from near base and expand to cover most of cnidosac except extreme apex [6].  
Rhinophores
Slightly wrinkled [7]. Translucent white with longitudinal white pigment line from posterior of base to apex, where it expands to often almost completely cap distal quarter of rhinophore.
Head
Long mobile oral tentacles, translucent white with longitudinal white pigment line from apex to head where unites with dorsal body line [7]. Mouthparts ventrally cleft [3].
Foot
Translucent white. Anterior expanded into curved wedge shaped propodial tentacles, often forming crescent in ventral view [3].