There's a wealth of biodiversity hidden beneath Singapore's waves.

On Mar. 14, Robert Tan discovered a rare, and rather remarkable creature while diving near Pulau Hantu.

10-cm octopus

57-year-old Tan is an experienced diver — he shared with Mothership that since 1994, he has carried out 1,418 dives, and spent 1,283.8 hours at Pulau Hantu alone.

With that much time spent in the murky waters of Singapore, he has seen quite a few uncommon creatures, including the elusive frogfish.

However, the blue-ringed octopus is one of the rarest.

Tan said that he had been guiding two others during a lazy Sunday morning at the offshore island.

They had descended to a depth of around 10m, when they caught their first glimpse of the magnificent marine animal.

The octopus was well-camouflaged, perched atop a rock.

Shining a light on it, Tan said that its blue rings glowed in the water.

Spooked by the divers' presences, the roughly 10cm-long creature soon swum off.

Here's a video of the amazing sighting that Tan put together .

Extremely venomous

The blue-ringed octopus is one of the most distinctive ocean creatures, firstly for its brightly luminescent blue rings that cover its head and tentacles.

Aside from its appearance, it's most famous for its venom, which packs quite a punch, even to humans.

It's venom is a thousand times more powerful than cyanide, and has enough venom to kill 26 adult humans within minutes.

The toxin blue-ringed octopuses produce is called tetrodotoxin, which can be found in pufferfish and is more potent that any produced by land mammals.

When stung by a blue-ringed octopus its venom first blocks nerve signals, causing one's muscles to go numb.

Other symptoms include nausea, vision loss or blindness, loss of senses and loss of motor skills. Ultimately, the victim will experience muscle paralysis, which leads to respiratory arrest.

Additionally, there is no anti-venom specific to the blue-ringed octopus available.

Second reliable record in Singapore

In response to queries, the Lee Kong Chian Natural History Museum told Mothership that this is likely only the second reliable record of a blue-ringed octopus in Singapore.

According to the museum's mollusc curator Tan Siong Kiat, one species of blue-ringed octopus — there are four blue-ringed octopus species around the world — was first recorded in Singapore in 1990.

However, this specimen could have been misidentified as the species recorded is mainly found in Southern Australia, which makes this record unreliable.

The next published record was in 2000, which could have been based off a specimen collected in Siglap in the 1930s.

Although the museum curator was unable to identify the species of blue-ringed octopus photographed at Pulau Hantu, this makes Tan's sighting the second reliable record of the octopus in Singapore.

In 1986, a six-year-old boy was believed to have been killed after being bitten by a blue-ringed octopus at East Coast Park, although it is uncertain if the culprit was definitively a blue-ringed octopus.

Nevertheless, deaths from blue-ringed octopuses are few and far between — they are not aggressive and will only attack when provoked or handled.

Their vivid colouration thus acts as a warning signal to both predators and humans.

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Top photos courtesy of Robert Tan