Nudibranch, the sea slugs losing their shells after going through the process of evolution

The pictures and explanations of sea slugs contained on the Eart Porm site have been crowned by a passionate title: "17 Sea Slugs That Prove Aliens Already Exist On Planet Earth"! (1) Wow! But unfortunately, there is no more satisfactory explanation for the statement. But apart from that statement, however, the sea slug that has lost its shell is really a charming water creature.

Nudibranchs are a group of soft-bodied, marine gastropod molluscs which shed their shells after their larval stage. Currently, about 2,300 valid species of nudibranchs are known.(2). I found one of them near Kuala Giging, one of the coastal areas in Aceh, east of Banda Aceh City, a few days ago.

This discovery draws attention to the distribution and habitat of these soft-bodied creatures.

Nudibranchs are benthic animals, found crawling over the substrate.(3). This is a reality when I found this animal. It is one of benthos, that is organisms living in benthic zone. (4)

Furthermore, Nudibranchs live at virtually all depths of salt water, from the intertidal zone to depths well over 700 m (2,300 ft). The greatest diversity of nudibranchs is seen in warm, shallow reefs, although a new nudibranch species was discovered at a depth near 2,500 m (8,200 ft). (5)

This group includes some of the most colourful creatures on earth. In the course of their evolution, nudibranchs have lost their shell while developing alternative defense mechanisms. Some species evolved an external anatomy with textures and colors that mimicked surrounding sessile invertebrate animals (often their prey sponges or soft corals) to avoid predators. (6)

Something that also seems very important to know about this creature is that Nudibranch has a Nematocyst toxin capable of killing jellyfish in size 50x larger than its body size. This Nematocyt toxin will attack the nerves and can disrupt the performance of the heart. And the poison can make people affected, moaning pain. But the Nudibranch is immune to its poison because it has a layer of mucus in its mouth that protects it from the nematocyst.(7)

Sources:

1. http://www.earthporm.com/sea-slugs/
2. https://en.wikipedia.org/wiki/Nudibranch
3. https://en.wikipedia.org/wiki/Benthic_zone
4. https://en.wikipedia.org/wiki/Benthos
5. http://biodiversitywarriors.org/isi-katalog.php?idk=7051&judul=Siput%20Laut%20Tidak%20Bercangkang
6. http://www.seaslugforum.net/