Sea Anemones


Sea Anemones belong to the order Actiniaria within the Phylum Cnidaria. Throughout world seas there are estimated to be over 1000 species of Anemones that live from low tide level in pools, to beyond 300 metres.

Basically, a Sea Anemone is a large solitary polyp that has no skeleton. It has a basal, or pedal disc that is capable of movement, either by crawling, digging, or both. This disc can be extremely adhesive and when attached to a hard substrate, nothing short of partial destruction can move it.


The highly muscular body, called a column, is capable of enormous expansion and contraction and may be smooth, lumpy or rough. At the top of the body (column) is the oral disc that is fringed with numbers of tentacles amounting to six, or multiples of six, arranged in various ways according to the species. At the centre of the oral disc is the mouth leading to the stomach. The stomach has powerful enzymes and can digest most prey, but as the animal has no rectum, any indigestible matter and waste is ejected through the mouth.

The body and tentacles have thousands of microscopic stinging cells called nematocysts embedded in the skin; those in the tentacles are generally more powerful and act in defence and prey-catching roles. Most Sea Anemones feed on plankton, but are able to kill and eat medium-sized Fish.

Sea Anemones can reproduce sexually and asexually. Each animal is either male or female and during the spawning season eggs and sperm are released (generally at night). A fertilised egg grows into a free-swimming larva called a planula (same as corals) that is then carried around by the currents until it settles to the bottom.

Semon’s Anemone Phyllodiscus semoni an Extreme Stinger

Rarely observed, Semon’s Sea Anemone ranges from the Philippines south to Indonesia. It’s a nocturnal species that expands out of its ‘hidey hole’ in the reef during late afternoon or at night, it’s also often out during the day, but few recognise it. This species grows to 30 cm (12 in) and may appear as a soft coral, or even a piece of the reef.


Semon’s Anemone can be green, bluish, brown, or cream and may be seen out on the coral reefs, rocky reefs and rubble areas across the Indo-Pacific to the South Pacific.


This is an extreme stinger and can sting through the toughest human skin and has caused many unpleasant wounds to snorkelers without protective body wear.

Semon’s Sea Anemone is a cryptic species with a number of appearances and due to its colouration is very difficult to see in the shadowy recesses of the reef.

As it expands at night, it has an oral tube that rises on a column above the rest of the disc.


However, it is not the tentacles around this extended mouth, that sting, it’s the fringing ones around the body that do the deed.

During the day in some areas of Indonesia, the body of Semon’s Anemone may form a shape similar to a Stony Coral, the reason for this is unknown, but may have something to do with luring Fish to take protection amongst its branches.


Never touch anything, even a brush against unprotected skin is a traumatic experience. Semon’s Anemone sting brings about deep-seated blistering and abundant pain.


There is a record of a Philippine spear fisherman on the island of Bohol who was badly stung and refused treatment, regardless of the excruciating pain. Within three days he passed away.


Potentially deadly stinging tentacles (nematocysts) Deadly poisonous to eat.


Do not allow this species to come in contact with any part of the unprotected body. Divers, underwater photographers and snorkelers should always wear full body suit and gloves when underwater, as protection from stinging marine life; this species has proved deadly.

Learn more about Sea Anemones and other Venomous Marine Life.

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