Colorful jewels of the sea: The wonderful world of sea slugs

Sea slugs are sometimes called the "jewels of the sea" because of their colorful and gorgeous appearance. There are surprisingly many of them in the waters around the world, and they can be found in tide pools and shallow waters, making them a popular subject for observation among divers and animal lovers.

Sea slugs have a strange appearance with their wavy bodies, protruding horns, and bushy gills, but they are actually a type of snail shell. According to the Japanese website of the Osaka aquarium Kaiyukan, the larvae often have shells.

Their ecology varies depending on the species. Generally, they live by feeding on sponges and sea squirts, but there are also some that eat poisonous jellyfish, and some that photosynthesize using chloroplasts taken from algae. Most species are small, only a few centimeters in length, but according to the Kaiyukan website, there are also large species that can reach several tens of centimeters in length.

Sea slugs usually hide quietly at the bottom of the ocean, exuding a mysterious charm. This time, we'll take a look at some photos of these colorful and graceful sea slugs that can be found in Japan.

The most representative sea slug that can be found in Japan is the blue sea slug. It has a flashy color scheme with a blue background, yellow borders, and orange antennae, making it the quintessential sea slug. It lives in shallow waters all over Japan, from Hokkaido to Kyushu.

Image: Photo AC

On the other hand, this is the yellow sea slug, which stands out with its unique appearance with its bright black and white spots on a yellow background and covered in spines. The photo was taken on the Izu Peninsula, but it is widely distributed around the world.

Next up is a cute pastel-colored sea slug. The photo was taken in Indonesia, but the ones found in Japan tend to be ivory-colored or white, as their Japanese name suggests.

The yellow-spotted sea slug has a white body dotted with yellow and orange spots. Despite its cute appearance, it is known as the gangster of the sea slug world because it preys on other sea slugs.

This is a species of the genus Asclepias. The purple spots on a white background make it look like something out of a fairy tale.

This sea slug with graceful frills around its body is called the meringue sea slug, and can be found in Okinawa Prefecture in Japan.

Sea slugs are often thought of as creatures that crawl quietly on the ocean floor, but some can actually swim by flapping their bodies. This Mikado sea slug is also known as the "Spanish dancer" because the way it dances in the ocean makes it look like it's wearing a flamenco costume. By the way, this is a large species that can reach a total length of 60 centimeters.

As its name suggests, the spotted sea slug boasts a simple yet sophisticated design of black spots on a white background. It lives in warm seas, and in Japan it can be found mainly in the seas of Kyushu and Okinawa Prefecture.

At first glance it appears plain due to its black body color, but the orange color of its antennae and gills add an accent that gives it quite a cool charm.

This is a white-banded sea slug with a beautiful wave pattern on its cream-colored back. It has a habit of fluttering its frill-like mantle.

The horned slug is characterized by its appearance that resembles an elongated Japanese konpeitō candy. According to the Okinawa Churaumi Aquarium website, some individuals have yellow tips and some do not. In Japan, it lives in the seas of Okinawa Prefecture.

This sea slug has a very cute combination of pale blue and navy blue stripes.

Although their tropical colors of orange, yellow, white, and purple, they actually live in Japan and can be seen not only in Okinawa Prefecture, but also along the coast of Wakayama Prefecture, which is known for its abundance of sea slugs, and on the Izu Peninsula.

The yellow tiger sea slug has a striking contrast between yellow and black. Because its coloring and pattern resemble a smiley face, it was once called the "smiley sea slug" or "smiley-face sea slug."

As its name suggests, the starry sea slug is particularly eye-catching with its starry sky-like pattern. According to the Churaumi Aquarium website, it lives by eating pale purple sponges.

Leopard print is synonymous with unique fashion, but there are also some leopard-print sea slugs in the world. In Japan, they can be found in the seas of Okinawa and Wakayama prefectures.

This is a type of sea slug in the genus Polytrichum. It looks a bit like a snail, so it makes sense that sea slugs are also part of the gastropod family.

The elegant wine-red sea slug, the Chirimen sea slug, has a slightly unusual ecology. According to the Science Portal website run by the Japan Science and Technology Agency, this sea slug cuts off its copulatory organs every time it mates, but it quickly regenerates them. This kind of creature is apparently the only one known to exist.

Next up is a species of Sakishima sea slug that stands out for its psychedelic coloring. All sea slugs have fluffy protrusions on their backs, but this is not just for fashion. Some species absorb stinging cells (i.e. poisonous stingers) from their food, jellyfish and sea anemones, and store them in the protrusions on their backs to protect themselves. But the sharpness is not just for appearance...

By the way, do you know how sea slugs are born? The color and shape vary depending on the species, but sea slug parents generally lay a spiral-shaped egg mass like the one in the photo. By the way, sea slugs are hermaphroditic, with the front part of the body being male and the back being female.

A common sea slug resting on a sponge. Is it eating?

The last one we'll introduce is a strange type of shrimp called the sea slug. It lives hidden on the surface of sea slugs and sea cucumbers, but it seems impossible for a sea slug of this size to live there...