Biodiversity & Conservation

A sea slug - Cadlina laevis

Cadlina laevis

Image Fiona Crouch - Cadlina laevis with encrusting red algae at Doune, Scotland.
Image copyright information

  • #
Distribution map

Cadlina laevis recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

Sightings Have you seen Cadlina laevis?
If so please submit your record.

Cadlina laevis is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Mollusca Snails, slugs, mussels, cockles, clams & squid
Class Gastropoda Snails, slugs & sea butterflies
Authority Linneaus, 1767
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland This species is frequently recorded around most coasts of the British Isles.
Habitat information icon Habitat information Cadlina laevis is common among Lithothamnion covered rocks from the shore to the sublittoral. It can be found primarily on its prey, the sponges Halisarca dujardini and Dysidea fragilis.
Text page icon Description Cadlina laevis 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.
Identifying features
  • Flattened oval body up to 3.2 cm in length.
  • Body, translucent white.
  • Opaque white or lemon-yellow pigmented mantle edge and glands.
  • Upper surface covered in small, conical, opaque tubercules.
  • The rhinophores are lamellate often with a yellow tip.
  • The oral tentacles are short, broad and flattened.
Additional information icon Additional information 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 dujardiniand 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).

This review can be cited as follows:

Sonia Rowley 2008. Cadlina laevis. A sea slug. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/11/2015]. Available from: <>