This Slug Should Be Impossible

Sacoglossan sea slugs (sap-sucking sea slugs) steal chloroplasts from algae and perform photosynthesis themselves—unprecedented among animals. The “leaf sheep” (Costasiella kuroshimae) exemplifies this impossible biology.

Sacoglossan sea slugs possess the unique ability to intentionally sever their own heads and regenerate entire bodies from just the head. No other animal on Earth demonstrates this behavior.

Sacoglossans comprise small marine gastropods known for vibrant colors, leaf-like shapes, and chloroplast theft ability. Species range from tiny 7mm individuals to 5cm slugs resembling floating seaweed or decorative lettuce.