‘You’d want one as a pet’: the irresistibly cute solar-powered sea slug

A neon green punk sheep that lives underwater. A solar-powered slug that can perform photosynthesis. If you are seeking beauty, brains and a wonderfully innovative lifestyle, then vote leaf sheep.

The leaf or sea sheep, Costasiella kuroshimae, is a sea slug about the size of a grain of rice. Like a sheep, it grazes on green stuff – certain species of algae, which it finds in tropical waters around Japan, Indonesia and the Philippines. But its sheepy nickname does it a disservice because it is far more ingenious than us land mammals.

This animal is not only powered by the algae it grazes, but by the sun. In a process called kleptoplasty, the leaf sheep steals the algae’s chloroplasts, the structures that plants use to capture sunlight and perform photosynthesis. It sequesters the intact chloroplasts within its own cells, storing them inside leaf-like branches on its back called cerata. These act like solar panels and enable the slug to power up via photosynthesis.

Wisely, the beady-eyed leaf sheep lives where it feeds, on Avrainvillea, a velvety type of algae that grows in fine silts around shallow reefs.

The leaf sheep’s vivid green cerata, which often feature white, pink or purple tips, provide chemical defences for this tiny animal. They give the leaf sheep its vivid green colour, which ensures it is beautifully camouflaged against the algae, which it locates via two ear-like structures above its eyes called rhinophores. These tentacles are sense and taste receptors, helping it find food and make sense of its world.

The leaf sheep’s vivid green cerata, which often feature white, pink or purple tips, provide chemical defences. Photograph: Oksana Maksymova/Alamy

The leaf sheep was only described by science in 1993 and has soared in popularity in recent years thanks to advances in underwater and macro photography, which have enabled us to appreciate its irresistibly cute appearance.

It must be an early favourite for invertebrate of the year 2026 because readers from around the world have nominated it, for its ingenuity and its looks, which have many echoes in popular culture from Shaun the Sheep to Pokémon.

“It looks like a Pokémon that you’d never want to use in battle but would definitely want as a pet,” says Matt, from Colorado. Shaymin Pokémon, to be precise, says Rei, aged nine, from Devon. Children know cool when they see it, and the leaf sheep’s inspiring example of harnessing energy from the sun certainly chimes with our times.

• It’s invertebrate of the year again! From August 3-12, every day we’ll be profiling one of the thousands of amazing invertebrates that our readers have nominated, and then, when you’ve got to hear about all of them, we’ll open the voting so you can choose your favourites. Don’t hesitate to get in touch with thoughts and ideas: email us at environment.desk@theguardian.com with Invertebrate in the subject line.