Is Aplysia a rabbit in the sea? I heard it can photosynthesize?

If you simply think it is a rabbit in the sea, you are wrong.

Because it has two cute protrusions on the top of its head, it looks like a cute little rabbit from a distance, so people named it sea hare .

In fact, sea slugs belong to the phylum Mollusca , while the domestic rabbits or hares we commonly see belong to the phylum Mammalia, and the two are very different [1].

Animal or plant?

Just because you see that sea slugs are molluscs, do you conclude that they are real animals ?

We know that whether or not plants and animals can carry out photosynthesis is an important basis for judging them. It is generally believed that plants contain chloroplasts, and the chlorophyll in the chloroplasts can use sunlight, air, and carbon dioxide to carry out photosynthesis , but animals cannot.

However, there are some sea slugs living in the New England region of the United States and the saline-alkali beaches of Canada that are emerald green all over. Scientific research has proven that such sea slugs can carry out photosynthesis !

How do they do it?

It turns out that sea slugs that can perform photosynthesis usually feed on specific seaweeds. After the seaweed is ingested, most of the cytoplasm is digested and absorbed, and the chloroplasts are miraculously preserved. However, chloroplasts alone are not enough, and the genes necessary for synthesizing chlorophyll are also needed. After analyzing the DNA sequences in the reproductive cells of sea slugs, scientists found that these cells themselves carry these genes, and their offspring almost perfectly inherit these genes, so that they can perform photosynthesis from generation to generation. Therefore, sea slugs are an animal that can produce the plant pigment - chlorophyll [1].

Attack or defense?

Although sea slugs are small in size, they are very good at avoiding enemies.

First, their body color changes according to the color of the algae they eat. For example, sea hares that eat brown algae such as kelp have brown body color, while sea hares that eat red algae have red or rose body color. This mechanism of changing body color is beneficial to their self-protection.

Second, it has two glands in its body. One gland is located under the mantle. When it encounters an enemy, it can secrete a purple-red liquid, which turns the seawater purple, thereby blocking the enemy's sight and allowing it to escape. In addition, it has a poison gland located at the front of the mantle, which can secrete a liquid with a slightly acidic smell. It is very unpleasant. If the enemy comes into contact with it, the mildest case will be poisoned and injured, and the worst case will die directly[2].

Boy or girl?

The reproduction method of sea slugs is also very interesting. Sea slugs are hermaphrodites, which means they have two reproductive organs.

During the breeding season, usually several or even dozens of conjoined pairs mate together: usually the female reproductive organ of the first one mates with the male reproductive organ of the second one, and the female reproductive organ of the second one mates with the male reproductive organ of the third one. This method of reproduction is very rare in nature.

Spawning occurs during mating or a few hours after separation. The eggs are glued together by a colloid secreted by the albumen glands, forming a long, thin rope-like egg cord. Some of these may be several hundred meters long. An 18-meter-long egg cord may contain more than 100,000 eggs.[2]

Do you know anything about this kind of sea hare?

References:

[1] Ocean World, Issue 01, 2009

[2] Aquarium, Issue 01, 2015