Nudibranchs – More Than Colourful Slugs!

September 20th, 2021 • uwt

Are you a nudibranch enthusiast? Do you love them so much you ignore everything around you when you spot a sea slug? Will you ignore a dozen manta rays flying over your head when you spot a brightly colored patch on the bottom that may be a nudibranch? Do you encounter a lot of confused looks when you pronounce the latin names of even the most common of nudibranchs? If any of these apply to you then you may just be a nudi nerd!

Mating Nudibranchs

Nudi Nerd is simply a playful name given to nudibranch enthusiasts. If you have ever met one, you understand how they know dozens of these beautiful creatures by their latin names. If they don’t happen to know the name by heart, they always have their handy dandy nudi i.d. book close at hand! It’s easy to spot a nudibranch lover underwater, they are often found close to the bottom with their eyes looking down.

What is a Nudibranch?

What exactly is a nudibranch? Simply stated, they are slugs that live in the sea. There are more than 3000 species and are found throughout the worlds oceans. They are a type of mollusk, and their name means “naked lung”. This refers to their external gills, the flowery looking appendage found toward the rear of the slug. Their bright colors make them rather conspicuous but it’s believed the colors act as a warning to potential predators. Although a few may be toxic, it’s more likely the warning is about how bad the slugs taste.

Nudibranchs with Shrimp


Another incredible fact about nudibranchs is the fact they are asexual. Two specimens of the same species will mate to exchange gametes and both will then lay eggs. Their egg cases come out as a ribbon shape containing hundreds of thousands if not millions of eggs. Although the ribbon looks enticing, they are protected by the toxins of sea sponges that the nudibranchs have eaten. The juvenile nudibranchs mainly look the same as the adult, only smaller.

What do Nudibranchs Eat?

Nudibranchs eat a variety of food: mainly sponges, hydroids, jellyfish, and tunicates. However, there are several species that feed on nudibranch eggs or even cannibalize other nudibranchs including their own species! Many of the foods they eat contain toxins (such as jellyfish) and the nudibranchs are able to adapt these toxins as part of their defense system on their skin.

Intricate Nudibranchs

Although they have a variety of interesting attributes, it’s most certainly their colour and shape that makes them enticing to divers. The gaudy shapes range from flat slugs to others which more resemble a banana bunch. With sizes ranging from less than 1cm to more than 30cm, some easily stand out while others are very hard to find. A practiced eye is needed as well as knowledge about their favorite habitats in order to find them. With more than 1000 species found in Indonesia alone, there are always interesting new species to find while diving.

Our Inner Nudi Nerd

We also love searching for nudibranchs. Although we can’t rattle off the Latin name of dozens of sea slugs, we are certainly enthusiasts of these beautiful creatures. When on the hunt for macro subjects, there is nothing more exciting that stumbling upon an intricate species that you have never seen before. Trying to capture them on camera is always a fun exercise. Not only as a tool for identification, but also to showcase their intricate colours. Many photographers love cataloguing the nudibranchs they encounter but another way to photograph them is a bit more artistic. Instead of taking an identification style photo, try to capture their more intricate style and shoot them more artistically. This shows the real beauty of these charismatic sea slugs to a better degree.