We’ve discussed cnidarians in this column several times and will likely do so many more. There are about 10,000 species in this phylum and since most of them live in the ocean, divers encounter them all the time. Many are photogenic, which is why my files are full of their images.
The two forms of cnidarians, polyps and medusae, are, according to The Shape of Life, “essentially mirrors of each other.” Polyps (i.e., anemones) are attached to a surface on one end by the pedal disk, while the oral disk at the other end is unattached and ringed with tentacles. Medusae (i.e., jellyfish) are unattached, upside down versions of polyps.
Although some cnidarians are polyps in one stage of their lives and medusae in another, sea anemones are always polyps. Their pedal disk has a sticky bottom that adheres to the substrate and can even move them from place to place. In the middle of the oral disk is an all-purpose opening that ingests food, eliminates waste and may even expel eggs/sperm. The area between the oral disk and the pedal disk is called the column.
Because sea anemones are often colorful they attract attention — but predators beware, they have weapons in the form of tiny, barbed harpoons (nematocysts) that can be used to repel unwanted advances and catch food. The harpoons, however, are too tiny to pose a danger to divers.
The phylum name Cnidaria (the “C” is silent) means, “nettle” in Greek. In addition to sea anemones its members include corals, sea pens, gorgonians, jellyfishes and hydroids. Most are carnivores and have nematocysts. Many types of anemones are found living in crevices in the reef. The anemones chosen for this article are different from most others of their species. Two species mentioned here are typically found in sand or rubble patches on the seafloor. Two species of yellow anemone encrust hard surfaces or gorgonian sea fans.
Burrowing tube anemone (Pachycerianthus fimbriatus): The burrowing tube anemone (Pachycerianthus fimbriatus) creates a protective tube that has been described as leathery, felt-like and parchment-like. It does this using specialized stingers, which, according the Wild Fact Sheets website, produce adhesive strips that mat together with sand and slime and harden. The sturdy tube remains on the seafloor long after its original inhabitant has perished, providing a home for a variety of other creatures. Only a small portion of the tube is above the surface of the mud or sand, the rest can be as much as two feet below it.
Predators of the burrowing tube anemone include several nudibranchs, most especially Dendronotus iris. While eating or attempting to eat the tentacles, these sea slugs are often pulled into the tube when the anemone seeks refuge deep inside it. The tube anemones usually survive the encounter and their tentacles will grow back.
While some tube anemones look orange or red underwater, they appear brown in most photos. (If you can explain why, I’d love to hear from you.) These tube dwellers can also be white, black or yellow.
Like most anemones, Pachycerianthus fimbriatus has nematocysts. Its diet includes small invertebrates and plankton. The soft-bodied anemone can be 12 inches long and its tube, 2.5 inches in diameter. These anemones are found off the West Coast from Alaska to Baja, on sand and soft mud bottoms, from low intertidal to depths of at least 70 feet.
Sand anemone (Actinostella correae): Information on sand anemones is hard to come by. The one shown here may or may not be Actinostella correae. Those living in California are usually found in sandy or fine rubble patches that contain pieces of shells, urchins, corals or algae, many of which are remnants of the anemone’s prior meals. The column is buried and only the oral disc and tentacles are exposed. This is a small anemone and the tentacular crown is only about three inches in diameter. To escape predators or when disturbed, sand anemones can quickly contract their column and rapidly disappear into the sand. A shadow can elicit the disappearing act.
Sand anemones eat whatever comes in contact with their tentacles or wanders onto their oral disc, which is often covered with sand or otherwise camouflaged to blend into the background. The sand anemone diet can include fish eggs, algae, larval fish, shrimp, mysids and amphipods, etc. Like most anemones they can go without food for long periods of time, even months.
Anemone expert Shane Anderson says: “Sand anemones are also capable of detaching from the hard substrate and inflating their column and tentacles with sea water, which allows them to emerge from the sand and drift with the currents to a new location.”
The sand anemones can be nibbled upon by predators and is missing numerous tentacles, which will grow back. According to Guide to Marine Invertebrates: Alaska to Baja California, sand anemones are found in “Southern California, on sand and bedrock bottoms.”
Yellow anemones (Epizoanthus scotinus, Savalia lucifica): When I first encountered Savalia lucifica, I thought I had found a sea fan in a new color. Then I realized the yellow anemones were parasites, killing their host as they colonized its surfaces. (I suspect they eat the sea fan’s polyps but have not had this confirmed.) In May, June and July of 1980 I found similar small yellow anemones growing on the substrate at Farnsworth Bank and Ship Rock, Catalina. I hadn’t seen them there before even though I had dived those two locations numerous times since I was certified in 1973. The anemones turned out to be two different species, Savalia lucifica and Epizoanthus scotinus, which can be bright or light yellow, white or brown. The major difference between the two is that Epizoanthus scotinus encrusts walls and other hard surfaces while Savalia lucifica grows on gorgonian fans.
Both of these anemone-like cnidarians live in colonies, with individuals connected at the bottom of their columns by a layer of tissue. The columns of individuals and the connecting tissues may contain sand or other material. The individual polyps can be nearly two inches tall and a colony of Epizoanthus scotinus can be more than six feet wide.
Yellow anemones range from Santa Catalina to Baja, from low intertidal waters down to 177 feet. They reproduce asexually by budding and can also reproduce sexually.
The author wishes to thank Genny and Shane Anderson for their help in the preparation of this article.
Burrowing tube anemone (Pachycerianthus fimbriatus)
Sand anemone (Actinostella correae)
Yellow anemone (Savalia lucifica)
Yellow anemone (Epizoanthus scotinus)