8 Marine Invertebrates That Can Cause Injury When Touched

Divers are often very aware of the type of marine life that can cause injury, which usually come armed with razor-sharp teeth or venomous spines. However, there are many marine invertebrates that can cause injury when touched, whether intentionally or inadvertently. Because they have no means to quickly evade or fight predators, these organisms harbor serious toxins that can cause injuries ranging from mild contact dermatitis to complications with the respiratory and nervous system. Let's take a look at just a few invertebrates that can cause injury.


via flickr/mastrfshrmn

Although most sea sponges are harmless and contact with them usually results in mild abrasion, there are a few species that produce crinitoxins and can cause irritation and dermatitis. Three species that cause contact dermatitis are the red-beard sponge (Micronia prolifera), fire sponge (Tedania ignis), and poison-bun sponge (Fibula nolitangere). Most people don't feel anything after initial contact with a toxin-producing sponge. A burning, stinging, or itching feeling may begin hours or days later, followed by mild to severe pain, local inflammation, redness, joint pain, and swelling.

Sea Anemones

via flickr/Bernard Spragg

Sea anemones are some of the ocean's most varied and beautiful creatures, but a few of them produce strong toxins that cause injury. Sea anemones are close relatives of jellyfish and corals and bear similar stinging tentacles. The most toxic of Anemones is the Actinodendron plumosum, also known as the stinging anemone or Hell’s Fire anemone for its very painful sting. Found primarily in the Indo-Pacific, these anemones that look more like soft coral with feather-like branches. These branches possess nematocysts (tiny, venomous stinging cells) that cause intense pain, burning sensations, and/or itching.


via flickr/prilfish

A fireworm is a type of venomous bristleworm with bright orange or red coloration and white bristles along each side. The bristles are filled with venom, and can easily penetrate and break off inside human flesh if this worm is touched. Its venom produces intense irritation in the area of contact. The fireworm is abundant on reefs, beneath stones in rocky areas or in seagrass beds, and on some muddy bottoms.

Sea Cucumbers

via flickr/Mal B

Sea cucumbers may look relatively harmless, but when threatened, they quickly expel holothurin (a toxic compound with similar properties to soap) from their anus. Holothurin is a strong poison that paralyzes predators, allowing the sea cucumber to swallow them whole. If holothurin comes into contact with human eyes, the result may be permanent blindness.

Fire Coral

via BBM Explorer

Fire coral also goes by stinging coral, both of which aptly describe what you're in for if you touch it. Despite the names, however, fire coral is not a true coral. It is a colonial marine organism that is actually closely related to jellyfish and anemones. A fire coral sting causes intense pain that can last anywhere from two days to two weeks.

Crown of Thorns Starfish

via National Marine Sanctuaries

The crown of thorns starfish poses an insidious threat to not only the coral reefs upon which it preys, but humans as well. It takes its name from its thorny appearance and round, crown-like shape. These thorns are very sharp and can pierce neoprene, giving divers little means of defense other than staying a very safe distance away. Symptoms of contact with a crown of thorns starfish include sharp stinging pain that lasts for hours, constant bleeding, nausea, and tissue swelling that may persist for days. If the spines become embedded in the skin, they must be surgically removed.


via flickr/Ed Bierman

Hydroids are feathery creatures that are closely related to jellyfish, and are sometimes referred to as fireweed. They are colonial organisms equipped with powerful stinging cells (nematocysts) used for defense and predation. They affix themselves to virtually any stable surface, like rocks, seaweed, docks, and mooring lines, and are one of the primary causes of itching and skin irritation for divers that accidentally come into contact.

Sea Urchins

via flickr/Gregory “Slobirdr” Smith

Sea urchins are some of the most ubiquitous marine invertebrates that can cause injury if touched, which is all to easy to do on a dive if you aren't paying attention. Like the crown of thorns, the sea urchin is covered in hollow, sometimes venomous spines that embed in the flesh. However, the spines are typically too small to be surgically removed, meaning you must wait for them to eventually dissolve into or expel from the body. Depending on the species and whether it's venomous, coming into contact with a sea urchin may result in infection, pain at the wound site, or difficulty breathing as a reaction to the venom.

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