has a flattened, fragile oval body up to 3.2 cm in length. It is translucent white with opaque white or lemon-yellow pigmentation around the mantle edge. This species has distinctive white or lemon-yellow glands towards the mantle margin. The upper surface bears small conical, opaque white tubercules The underside is covered in a tracery of fine white markings. The front part of the foot (propodium) is groved to form two lips (bilaminate). Its white lamellate rhinophores are short and tapered, often with a yellow tip. The oral tentacles are short, broad and flattened. This species usually has 5 (rarely 6 or 7) tripinnate gills.Cadlina laevis
was the first British nudibranch noted to reproduce by direct development (Thompson, 1967). Thompson (1967) observed that the embryonic period lasted for ca. 50 days with a vestigial veliger phase of 7 days occurring within the eggs. Tiny adults emerged from the eggs and remained benthic, having sufficient food reserves to sustain life and apparent growth for over a week before active feeding commenced (Thompson, 1967). Cadlina laevis
feeds on encrusting sponges primarily Halisarca dujardini
and Dysidea fragilis
. Interestingly, individuals of this species found in the north of the British Isles tend to have a milky white pigmentation and are mainly found in the littoral feeding on Halisarca dujardini
. Individuals in the south and western parts of the British Isles have the distinctive lemon-yellow pigmentation and are mainly found feeding in the sublittoral on Dysidea fragilis
(Picton & Morrow, 1994; Picton, 2001). It has been suggested that these two distinctive colour morphs may be separate species but the variation may be clinal due to its reproductive strategy (Picton & Morrow, 1994).
This species spawns in March and its penis is armed with numerous tiny hooked chitinous spines. The tripinnate gills of this species retract simultaneously into a common branchial pit, a process known as cryptobranchiate (Thompson, 1988).