Berthellina edwardsii

Berthellina edwardsii is a large sea slug that typically reaches lengths of 5 to 6 cm. Its head features a pair of smooth, rolled rhinophores, while the triangular buccal veil and low-lying tentacles are less noticeable. The slug's body is translucent, allowing a view of its small internal shell, which appears whitish, and dark spots from the digestive glands can be seen through the dorsal surface. The coloration ranges from whitish or lemon yellow to deep orange-red, and it can be confused with similar species like Berthella aurantiaca and Berthella stellata, though B. aurantiaca has a larger internal shell and B. stellata is smaller and has a distinct star-shaped pattern on its back. This species is native to the northeastern Atlantic Ocean and the Mediterranean Sea, primarily inhabiting benthic environments. It is mainly nocturnal, seeking refuge during the day in cracks or under rocks. Berthellina edwardsii feeds on sponges and tunicates, using its radula to rasp the surfaces of its food sources. Breeding occurs in autumn, where individuals, being hermaphroditic, will exchange sperm while orienting themselves to bring their genital openings close together. They lay numerous tiny eggs in a whitish, coiled, jelly-like ribbon attached to the substrate. Encounters with Berthellina edwardsii during dives may reveal its distinctive coloration and behavior as it hides during the day. The species secretes a white acidic fluid from its mantle, which makes it distasteful to fish, serving as a warning of its toxicity. Conservation status for this species has not been evaluated, but it is recorded in various dive sites, indicating it may be relatively common in its habitat.