The Canadian Encyclopedia — neutral, cited, updated
July 26, 2026Sources cited
Canadianwire.
Canada’s encyclopedia & explainer
Home›Science & Nature›Marine Biology›Leaf sheep
Science & Nature • Marine Biology

Leaf sheep

The leaf sheep is the common name for *Costasiella kuroshimae*, a tiny sacoglossan sea slug known for its sheep-like appearance and green leaf-like appendages.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

The leaf sheep is the common name for *Costasiella kuroshimae*, a tiny sacoglossan sea slug known for its sheep-like appearance and green leaf-like appendages. It lives in shallow tropical waters and can perform photosynthesis for a time by retaining chloroplasts from the algae it eats, a process called kleptoplasty.

Description

Leaf sheep are tiny, shell-less sea slugs with a rounded body and leaf-like projections called cerata. Their appearance has led to the popular name, but they are not sheep and are not plants.

Habitat and distribution

They are found in shallow tropical marine environments in the Indo-Pacific, especially around coral reefs and algae-rich sandy areas. Sources commonly mention Japan, Indonesia, and the Philippines.

Feeding and photosynthesis

Leaf sheep feed on algae, especially *Avrainvillea*, and can keep the algae’s chloroplasts inside their own tissues. This kleptoplasty allows them to photosynthesize for a period after feeding.

Biology

The species is a sacoglossan gastropod, a group of sea slugs known for feeding on algae. Like other mollusks, it is an animal and must still obtain nutrients from food even though it can supplement energy through photosynthesis.

Key facts

  • The leaf sheep is a shell-less marine gastropod mollusk.
  • It is a sacoglossan sea slug in the family Costasiellidae.
  • It is usually associated with tropical Indo-Pacific waters, including areas near Japan, Indonesia, and the Philippines.
  • It feeds on green algae in the genus *Avrainvillea*.
  • It can retain chloroplasts from algae and use them for photosynthesis temporarily.
🍁
Canadian context

Leaf sheep are of interest to Canadian readers as an example of marine kleptoplasty and unusual animal adaptation, topics commonly covered in marine biology and environmental science education.

Frequently asked questions

What is a leaf sheep?
A leaf sheep is the common name for *Costasiella kuroshimae*, a tiny sea slug known for its sheep-like look and leaf-like body parts.
Is the leaf sheep a sea slug?
Yes. It is a sacoglossan sea slug, which is a shell-less marine gastropod mollusk.
Where do leaf sheep live?
They live in shallow tropical waters of the Indo-Pacific, often on or near algae in coral reef habitats.
Can leaf sheep photosynthesize?
Yes, temporarily. They can photosynthesize by keeping chloroplasts from the algae they eat, a process called kleptoplasty.
How big is a leaf sheep?
It is very small, usually about 5–8 mm long, though some sources describe it as reaching around 1 cm.
What does a leaf sheep eat?
It feeds mainly on green algae, especially algae in the genus *Avrainvillea*.

References

  1. Wikipedia — https://en.wikipedia.org/wiki/Costasiella_kuroshimae
    Supports: Common name, scientific name, classification, kleptoplasty, and diet on *Avrainvillea*.
  2. Oceana — https://oceana.org/marine-life/leaf-sheep/
    Supports: Habitat in tropical coral reefs, living on *Avrainvillea*, and photosynthesis via kleptoplasty.
  3. Live Science — https://www.livescience.com/animals/leaf-sheep-the-adorable-solar-powered-sea-slug-that-looks-like-shaun-the-sheep
    Supports: Sea slug identity, shallow-water habitat, diet, and approximate size.
  4. KÜRE Encyclopedia — https://kureansiklopedi.com/en/detay/leaf-sheep-costasiella-kuroshimae-6a608
    Supports: Sea slug classification, approximate length, and feeding on *Avrainvillea*.