NudiBranchs: The slugs of the sea

Our world consists of over 70% of water bodies; mainly oceans. The ocean is home to numerous different creatures. From those, the underwater creature I find most stunning is the Nudibranch. Their name comes from the latin word ‘Nudus’ and greek word, ‘Brankhia’, which means ‘Naked gills’ in English. Nudibranchs are soft bodied molluscs that are distinctive because of their bright striking colors and petite bodies. They live in almost every ocean such as the indian ocean and even in the southern ocean around Antarctica.

During a diving trip to Bali last summer, my dive master told me that Nudibranchs are usually referred to as ‘blind sea slugs’ because of their inability to see. However, after some research around the internet, I discovered that my dive master was only partially correct. Nudibranchs have eyes but they can only differentiate brightness from darkness instead of different shapes. Nudibranchs are also hermaphrodites; they can mate with any other nudibranchs they bump into. However, they are also semelparous, meaning that they can only lay eggs once in a lifetime and then die shortly after.

In the past, Nudibranchs had shells. However, after undergoing several phases of evolution, nudibranchs lost this trait but also developed other defense mechanisms. For example, they mimic the colors of corals and sea sponges to hide from their predators.

Although studying bigger animals such as sharks and whales are relatively more interesting, it is important that we know more about these sea slugs as they also play an important role in the ecosystem. Moreover, although they are small creatures, they hold toxins in their bodies from the sponges they eat, which are then released to keep predators away. These toxins are also dangerous to the human population as it is said to be toxic to our cancer cell lines.

The nudibranchs I usually encounter during my dives are the thecacera sp.1 (commonly known by divers as the pokemon), Anna’s Chromodoris, and the brown margin glossodoris.

The thecacera sp.1 are typically a translucent orange color with two long appendages. They have scattered dark spots around their bodies and are most common in Indonesia, Malaysia, and the Philippines.

Anna’s chromodoris are usually blue, bordered with black, white, and yellow. They are found mostly in Japan, Indo-west Pacific, and Vanuatu. Other nudibranchs that look similar to anna’s chromodoris is Coleman’s chromodoris, streaked chromodoris, and the magnificent chromodoris.

The brown margin Glossodoris features varying amounts of reddish brown on their bodies, with white and orange borders. They have a vertical white line at the front of their rhinophores (antennas) and also along their gill edges.