The world’s waters are full of fascinating creatures, from large sharks and intelligent whales to tiny species. Among them are sea slugs, or nudibranchs, a group of mostly small and slow-moving marine animals. With over 3,000 documented species, whether rare or common, nudibranchs always capture divers attention with their unique appearance and behavior.
The name "nudibranch" comes from Latin and Greek. The "nudi-" part is from Latin "nudus," meaning "naked," and "-branch" comes from the Greek "brankha," meaning "gills." So, nudibranch basically means "naked gills," which fits since these sea slugs flaunt their gills on the outside rather than hiding them under a shell.
Nudibranchs are famous for their wild colors and funky patterns, which help them blend in or stand out in their underwater world. They've ditched the shell their ancestors had, making their vibrant looks even more eye-catching!
Awesome facts about Nudis
Nudibranchs, despite their small size, use bright colors to warn predators that they might be toxic or unappetizing. This colorful warning, called aposematism, is a defense strategy used by many nudibranchs, including those in the Phyllidiidae family found in Koh Tao.
Nudibranchs have specialized sensory organs called rhinophores on their heads, which function like antennae to detect chemicals in the water. These organs help them locate food, find mates, and navigate their surroundings. Rhinophores vary in shape and size, often being long, slender, or intricately branched. They not only assist in finding prey and mates but also play a role in avoiding predators. Some species can even retract their rhinophores when threatened. Besides rhinophores, nudibranchs have other chemosensory structures called cerata - those colorful, branching structures on their backs - which are used for respiration and digestion. These structures can also help in defense by producing toxins.
Some nudibranchs have specialized adaptations to absorb toxins from their prey for their own defense. Here are a few examples:
Phyllidia spp.: These nudibranchs feed on toxic sponges and use the toxins for their own protection. Their bright colors and patterns serve as a warning to potential predators.
Chromodoris spp.: This genus, including species like Chromodoris annularis, consumes sponges and can retain the chemicals in their tissues to deter predators.
Flabellina spp.: These nudibranchs feed on hydroids, which contain stinging cells. They can incorporate the stinging cells into their own defense system.
Nudibranchs have some impressive regeneration skills. If they lose a part of their body, like a ceras, they can regrow it. The process involves specialized cells that can differentiate into various types of tissue needed to replace the lost structures. This ability to regrow complex parts helps nudibranchs recover from injuries and continue their lives. It also plays a role in their defense mechanisms, as losing parts might distract or deter predators.
Their reproductive system is intriguingly complex: both male and female reproductive organs reside closely within their bodies. Though the details may differ among species, typically, the female system comprises a vagina, semen receptor, and various egg-producing glands. Conversely, the male system includes the prostate, sperm duct, and ejaculatory duct. When nudibranchs mate, they're all about equality - they fertilize each other and both get to lay eggs! It's a team effort: they line up their genital pores (those openings on their right sides of their body) and then get busy with the copulation. Talk about multitasking (Then can mutually and simultaneously penetrate each other!) Certain species possess disposable penises; an unusual evolutionary trait. Yep, shed their penis after use, regrowing a new one within 24 hours, equipped with coils for future use! Some other species of nudibranchs like to inject their partner with prostate fluid in the head! Storing sperm next to the brain might seem like a strange choice, but hey, who are we to judge? Maybe it's their way of spicing up the relationship or ensuring their legacy lives on in their mate's offspring! Scientists are still scratching their heads over this peculiar behavior.
Curious about the wild world of marine life? Check out our 'How Do Fish Have Sex?' Blog for some surprising tales of underwater reproduction!
In Koh Tao, you'll find a variety of nudibranch species
You’ll find a variety of nudibranch species at any dive site in Koh Tao—it's a haven for macro lovers! Here’s just a sneak peek of the incredible nudibranchs we can spot around Koh Tao:
