Grey Side-Gilled Sea Slug

Pleurobranchaea maculata

This species of sea slug reaches lengths of 80 to 100 mm, with southern specimens often larger. It has a mottled pale grey coloration, marked by short, broken brown lines. The wedge-shaped head features two sensory tentacles, while the mantle appears smooth but is covered with folds and puckers. The foot extends beyond the mantle, and the feathery gill is tucked under the right side. The absence of a shell distinguishes it from other molluscs. Pleurobranchaea maculata is primarily found in the intertidal zone and can inhabit depths of up to 6 m or deeper, often off rocky coasts. Its distribution includes New Zealand, southeastern Australia, China, Sri Lanka, and Japan. Notably, it has been reported far outside its native range along the coast of Argentina, where it has spread rapidly. As an opportunistic carnivore, this slug feeds on a variety of soft-bodied invertebrates, particularly sea anemones, but also marine worms, mussels, and even other sea slugs. It reproduces by laying small eggs that hatch into planktonic larvae, which settle after about three weeks. The lifespan of this species is typically 2 to 3 years, with spawning occurring in winter. Encounters with this sea slug during dives can be intriguing, as they may be observed in their natural habitat, often washed ashore during storms. While they are generally harmless, there was a notable incident in New Zealand related to tetrodotoxin poisoning, which raised awareness about their potential toxicity after several dogs ingested them.