Pretty But Poorly Understood Polyps: Sea Anemones

Among the approximately 10,000 species that belong to the phylum Cnidaria (the ‚ “C” is silent), there are at least 100 that are dangerous to humans. The phylum name means “nettle” in Greek and its members include sea anemones, corals, sea pens, gorgonians, jellyfishes and hydroids. Most of them are carnivores and most have nematocysts, which are used for defense and catching food. Fortunately, sea anemones are not dangerous to humans; their tiny harpoons (nematocysts) cannot penetrate deep enough into our skin to deliver toxin to our pain receptors.

 
There are two cnidarian forms, polyps and medusae. 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. 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 (slowwwwly). In the middle of the oral disk is an all-purpose opening that ingests food, eliminates waste and may even expel eggs/sperm. The column is the area between the oral disk and the pedal disk.
Like many creatures that live in the ocean, the colors of same-species sea anemones can vary widely, as can the colors of individual animals. Also, scientific names and classifications change. There are anemones that look so much alike only lab work can determine their identity. The World Register of Marine Species (WoRMS) admits that some sea anemones “are poorly understood.” It’s best not to take anything for granted when it comes to sea anemone ID.
The four anemones I’ve chosen to feature here are all common off our coast. They include two that have been classified twice; one that has been classified three times and one that broods its young.
Sunburst anemone (Anthopleura sola): The Sunburst was long thought to be a larger, solitary form of the aggregating anemone (Anthopleura elegantissima), with which it shares a striking resemblance. Molecular techniques identified it as a separate species in 2000. While the oral disks of the aggregating are less than three inches in diameter, those of the sunburst can reach nearly ten inches. It would be unusual to see both anemones in the same area.
Aggregating and sunburst anemones have similar coloring. Their columns are covered with vertical rows of sticky tubercles that can hold small shells, sand and other debris. These anemones have special fighting tentacles (acrorhagia) just under and outside the ring of feeding tentacles. Both types of tentacles have nematocysts. When not being used to repel enemies, the acrorhagia are often retracted and hard to see. While aggregating anemones live in identical clone colonies, the solitary sunburst maintains an anemone-free space around it. 
A. sola sexes are separate and reproduce by cloning or spawning. When they spawn, the eggs and sperm released become free-swimming larvae after fertilization. Because so many are either eaten or can’t find a suitable place to settle, only a small percentage survives. 
Anthopleura sola eat a wide variety of fish, crustaceans and other marine invertebrates. They are found on rocky surfaces from Central California to Baja. This hardy species is unfazed by industrial pollution or sewage and even lives in tide pools. The one shown here was photographed in about 60 feet of water at Palm Park off Santa Cruz Island.
White-spotted rose anemone (Cribrinopsis albopunctata): I photograph nearly every white-spotted anemone I come across because each seems more beautiful than the last. This animal prefers colder waters and is found as far north as Alaska. It is usually solitary and if you find several in an area, they won’t be close together. Their diet includes sea urchins, small fish, crabs and mussels. Certain nudibranchs, sea stars and snails dine on them.
The white-spotted rose has a red to orange column covered with white dots. The pedal disk is brown to reddish brown or orange. The oral disk can be as much as six inches in diameter and the tentacles can be light gray, white, red, orange or even all three colors. 
The white-spotted rose’s scientific name was Tealia lofotensis when I started diving; it was reclassified as Urticina lofotensis for a while and became Cribrinopsis albopunctata in 2006.
Proliferating/brooding anemone (Epiactis prolifera): Every once in a while a marine animal tickles my fancy. The small white sea urchins that wear “hats” of seaweed, shells or tiny rocks were one, the proliferating/brooding anemones are another. The latter are so named because they reproduce year-round and their offspring live on their mother until they are old enough to take care of themselves.
E. prolifera anemones are gynodioecious, i.e., small adults are female, larger adults are hermaphrodites. They cross-fertilize, though some self-fertilization also occurs. After the eggs are fertilized inside the female they are expelled through the opening in the oral disk and hair-like cilia move them down the column. Specialized nematocysts and mucus keep them attached. The young live on the column until they are at least three months old and .157 inch in diameter, then crawl off. It is thought they eat small crustaceans.
Since these anemones reproduce year-round, the young living on their mothers are different ages, like the children in a human family. When you find numerous Epiactis prolifera in an area, they will also be different sizes/ages.
Brooding anemones are small, no more than two inches in diameter and less than one and one-quarter inches tall. They may be brown, green, orange, blue, gray, solid or blotched. There can be brownish-red or dark green stripes on column and occasionally the lower column and pedal disk are blue. The columns lack tubercles. 
E. prolifera ranges from southern Alaska to Southern California, from mid intertidal to subtidal waters. My photographs of them were taken in the Northern Channel Islands. Predators include shaggy mouse aeolids, leather stars and perhaps mosshead sculpins. 
Velvety red/fish-eating anemone (Urticina piscivora): This species was formerly Tealia piscivora. It is more aggressive than most anemones and doesn’t just wait for things to stumble into its clutches, it actually reaches out and grabs such creatures as shrimp and small fish with its tentacles. Like many anemones, U. piscivora grows larger when there is plenty of food and shrinks when it is scarce. It prefers rocky areas with current.
U. piscivora is a large anemone (almost eight inches tall and four inches in diameter), easily identified by its velvety-looking bright red column. The tubercles on the column are the same color and do not usually have anything stuck to them. The fish-eating anemone is found from Alaska to La Jolla, from intertidal waters to about 160 feet. The one shown here was photographed off Big Sur. 
Sea Anemone Stats
Phylum: Cnidaria
Class: Anthozoa
Order: Actiniaria 
Family: Actiniidae
Genus/species: Sunburst anemone (Anthopleura sola
White-spotted rose anemone (Cribrinopsis albopunctata)
Proliferating/brooding anemone (Epiactis prolifera)
Velvety red/fish-eating anemone (Urticina piscivora)
Reproduction: Cloning and spawning
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