The leaf sheep, or sea sheep (Costasiella kuroshimae), a sea slug approximately the size of a grain of rice, is an early favourite for Invertebrate of the Year 2026. This creature has gained popularity for its unique ability to harness energy from the sun.
The sea slug grazes on certain species of algae found in tropical waters around Japan, Indonesia, and the Philippines. Through a process called kleptoplasty, it steals chloroplasts from the algae and stores them within its own cells. These chloroplasts are then used to perform photosynthesis, allowing the slug to power itself.
The leaf sheep's vivid green cerata, which are leaf-like branches on its back, function as solar panels. These cerata also provide chemical defences and camouflage the slug against the algae it feeds on. The animal locates its food using two ear-like structures above its eyes, called rhinophores, which act as sense and taste receptors.
First described by science in 1993, the leaf sheep's appearance has become more widely appreciated in recent years due to advancements in underwater and macro photography. Readers worldwide have nominated it for its ingenuity and distinctive looks.