Undersea Creatures of Nightmare

Anjani Ganase presents some marine creatures that have terrifying defence mechanisms. Fortunately, most of them are small and only make themselves visible when threatened. Look closely and maybe you’ll see which ones inspired monsters of fiction and film.

 

Slice and dice jaws

What buries itself in the sand, lying completely still in order to grab and pull an unsuspecting prey away into the underworld of coral reefs? The Bobbit worm invokes depictions of the sand monsters of sci-fi movies, such as Dune and Tremors. In real life, this worm is only a few inches wide but can grow up to 10 feet in length. Its razor-sharp jaws can chop a small fish into pieces. It was named after Lorena Bobbit who severed her husband’s private part. If that wasn’t enough, the worm also injects venom into its prey. The name Bobbit worm is actually used to describe least 50 species of predatory worms with similar behaviour, since the specimen collected could not be identified to species. The Bobbit worm occurs in the tropical shallow reefs of the Indo-Pacific and only poses a threat to small fish and crustaceans that live along the reef’s sandy bottom. Their antennae can detect small vibrations in the water above. However, some fish species can fight back; if Bobbit worm’s hiding place is found it, fish can blow jets of waters on the sand to force it out of hiding.

Bobbit worm. Photo by Jenny Huang. Creative Commons Attribution 2.0 Generic

Trapdoors for the unsuspecting

Tunicates represent a group of marine invertebrates that resemble sea squirts or salps.  They are typically attached to surfaces, have a rubbery appearance and two tubes for siphoning water for filter feeding. The predatory tunicate (Megalodicopia hians) occurs along the walls of deep-sea canyons in the temperate and polar Pacific Ocean around 5500 m down. They stand around 5 inches in height and stick out into the darkness. The predatory tunicates are known as the Venus flytraps of the deep sea, they wait opened mouthed for tiny fish or crustaceans (zooplankton) to swim past the cavernous mouth so that it can close around it.

 

Predatory tunicate. Photo by Eric Polk. Creative Commons Attribution-Share Alike 4.0 International

Turning their prey into zombies

Deadly things come in small sizes, especially in the ocean where 98 % of the ocean life is composed of micro-organisms. Phrominas are predatory marine amphipods (shrimp like appearance) that resembles the queen alien from the 1986 movie Alien. Phrominas kill gelatinous plankton, such as salps (barrel-shaped planktonic tunicate) by eating out their insides, residing in their hollowed-out bodies and laying eggs. The tissue of the salp barrel stays alive for a while, and retains its shape. The salp barrel gives the phronima a stable home that is buoyant and easy to move around with its egg safe from the exposed environment. They typically hunt in the twilight zone (low light depths) of the ocean and can make themselves invisible to predators and prey with specialized pigments. They are common in the temperate and tropical oceans.

 

Preserved specimen of Phromina amphipod. Photo courtesy Eric A. Lazo-Wasem

Toxic tentacles

The Australian box jelly (Chironex fleckeri) is an extremely venomous species of jellyfish found around Australia and Indo-Pacific. Their venom is known to cause crippling pain and death. During the spring period of Australia (September-October), these box jellies that typically occur in nearshore marine environments swim up rivers and gather for spawning. While the adults die after spawning, new-borns are carried out to sea by the river flow. Box jellies are very capable swimmers, able to swim against currents. They hunt small fish and shrimp by using their stinging cells to capture and kill prey. The only known predator of the box jellies are the green turtles, which have a thick skin that is impenetrable to the stinging cells. They are very dangerous to humans. It is estimated that if 6 m of box jelly tentacles come into contact with a human and all the stinging cells fire off, this would cause death in a few minutes. The Chironex species can have tentacles up to 3 metres long. While the typical exposure is a mere fraction of this, victims experience pain, shortness of breath, and even cardiac arrest. Symptoms may last for weeks.  Most of the deaths from the Australian box jelly are children and young adults. This is why stinger nets and stinger suits are recommended in tropical and sub-tropical areas of Australia, especially near river mouths during the spring and summer periods.

 

Sea wasp jellyfish. Photo courtesy Guido Gautsch, Toyota, Japan. Creative Commons Attribution-Share Alike 2.0 Generic license.

Blue rings for danger

Being venomous in the ocean almost comes with the territory when defending oneself in the busy benthic environment. Bright rings are displayed by the blue-ringed octopus when threatened; these should be fair warning to potential predators. This tiny cephalopod (only 12 cm in length inclusive of its arms) houses a deadly chemical that runs throughout its body and is made of a chemical called tetrodotoxin or TTX. The chemical is produced by symbiotic bacteria housed in their salivary glands. The toxin is used for hunting as well as for defence. TTX is a neurotoxin that causes muscle paralysis that eventually results in respiratory failure. The toxin is 1000 times more potent than cyanide and is the same toxin found in pufferfish. There is no antidote.  There are ten species of blue-ringed octopuses that occupy mainly coral reefs in the Indo-Pacific, and there are species that occupy deeper waters along Australia’s south coast and Tasmania. Incidents of humans being impacted by blue-ringed octopuses are largely unheard of except for the one case where a person consumed it.

Blue-ringed octopus. Credit: Jayne Jenkins / Ocean Image Bank

 

References

https://animaldiversity.org/accounts/Chironex_fleckeri/

https://www.nhm.ac.uk/discover/blue-ringed-octopus-small-vibrant-deadly.html