The Sea Sheep, or Costasiella Kuroshimae, is known by many different names. Leaf slug, leaf sheep, and salty ocean caterpillars are some of these. This marine invertebrate is one of the many species of sea slug and gastropod mollusks to roam the oceanic ecosystem. They have some incredible survival tricks up their sleeve and are not to be messed with. The adorable little sea slug, reaching only 1-5mm in length, is one of the most unique-looking sea creatures in the entire world.

Physical Appearance

One of the most interesting elements of the sea sheep is how it looks. It remarkably looks very similar to a plant and also a sheep. The Sacoglossan species creature has two black beady eyes and two long rhinophores. These rhinophores are like antennas that can detect the chemical makeup of the water in its habitat. This helps them to navigate, find food sources and protect themselves from predation. These rhinophores with black tips look like sheep’s ears, which is why they are known as sea sheep, and can also resemble antennae on insects.

The Sea Sheep is up there with sea bunnies as one of the cutest animals in the ocean. Incredibly, the sea sheep obtains its green, leafy color from a process called kleptoplasty. This is where the algal chloroplasts from the algae they eat remain in their body. This allows them to utilize carbon dioxide and sunlight to engage in photosynthesis, creating their own energy, similar to a plant-based lifeform, being one of the only sea creatures in the world able to do so (all others belong to the Sacoglossa sea slug clade). They have leaflike appendages called cerata, which contain the absorbed chloroplasts, and are akin in appearance to succulent plants, such as the Aloe Vera plant.

A species of sacoglossan sea slug, the Sea Sheep is a small marine animal, ranging from 5mm- 1cm, with the very biggest specimens only reaching 1 cm in adulthood.

Sea Slug (Leaf Slug)
The Sea Sheep strongly resembles a leaf


The Sea Sheep is a very picky creature when it comes to its diet. It tends to spend the majority of its life living and feeding on a type of sea algae called Avrainvillea. The leaf sheep’s rhinophores have fine hairs that sense chemicals in the water, allowing them to survive the chloroplasts found in the algae and then use the kleptoplasty function to supplement their diet even further. They are similar to solar panels in that they use their cerata to catch the sunlight, and the process of photosynthesis occurs, typically only performed by single-celled organisms. They generate enough energy to sustain their own bodies, making them solar-powered slugs.


The Sea Sheep has only been found in the Indian and Pacific ocean, near the Philippines, Japan, and Indonesia. They also occupy waters and reefs as far wide as Papua New Guinea, Singapore, and Northern Australia. They spend the majority of their lives on specific types of green algae, and use them to blend in.


Like many interesting marine creatures, the Sea Sheep has both reproductive organs, male and female, making them hermaphrodites. They still have to find a mate despite this. Once they find a compatible partner, they then work together to produce a mass of eggs. Once the eggs are fertilized, they will hatch into shelled larvae and end up as plankton. They can spend up to two weeks in this state until they develop into a sea slug.


Sea Sheep have the threat of predators but do a good job of avoiding conflict. Their algae-green appearance lets them blend into their surroundings. Their use of the chemicals from the algae has developed into a toxic defense mechanism. This helps deter potential predation.

Human intervention is a growing threat to the sea sheep with habitat loss. Pollution and illegal fishing are becoming more of an influence on the coral reefs. However, the sea sheep is not listed as endangered.

Facts about the Sea Sheep

  • Sea Sheep are completely hermaphroditic, meaning they possess both types of reproductive organs.
  • They are one of the very few animals on earth to use photosynthesis as a feeding process.
  • Sea sheep are not yet declared endangered but are suffering habitat loss.
  • They utilize the algae’s cells for energy and to create their toxins.
  • Sea slugs are closely related to gastropods, such as sea snails and mollusks, the main difference being the lack of shell.
  • They were only discovered less than three decades ago, so scientists don’t actually know how long leaf sheep sea slugs live for.


Are leaf slugs poisonous?

The sea sheep have a toxic defense mechanism to fight off bigger animals. They manufacture their poison using chlorophyll and other chemicals extracted from the algae, although they aren’t deemed to be a danger to divers.

Where are Sea Sheep found?

Sea Sheep are found mainly in the Indo-Pacific oceans. Ranging from Northern Australia to The Philippines. In the wild, they can be found exclusively on Avrainvillea, a type of algae that they live and feed on.

Can you keep a Sea Sheep as a pet?

It is not advised to keep a sea sheep as a pet. The knowledge of them as animals is very low, making it a difficult task to keep one in your fish tank.

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