Sea anemones

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Q 1.
	How do sea anemones feed?
Q 2.
	Are sea fans plants or animals?
Q 3.
	Is the sea anemone an animal or a plant?
Q 4.
	What is the "sea-pansy"?
Q 5.
	How do sea anemones feed?
Q 6.
	I am a marine collector. I would like to know the scientific name of the "passion flower" and the general areas where it may be found.
Q 7.
	I am interested in finding a source of information on the sea fan which is found in our waters. I have been told that Rhipidogorgia flabellum is the proper name for it, but I have been unable to find any information in either the dictionary or the Encyclopaedia Britannica. Can you help me?
Q 8.
	Is there any way sea fans can be preserved, especially as to color and pliability?
Q 9.
	I have heard the Japanese use sea anemones as food. Is this true?
Q 10.
	Can a sea anemone be kept in a home aquarium? Can fishes or other forms of marine life be kept with it?
Q 11.
	Diving off the island of Tobago, I observed a West Indian fighting conch, the shell of which was covered by a bright red thready growth. We were at 90 feet, below the level of red light penetration. The growth had the appearance of red propylene rope threads, and the color was very bright, resembling the warning red paint used on an aircraft. Do you have any idea what this might be?
Q 12.
	Can you identify this animal which I have found in the surf off Cocoa Beach, and have preserved in formalin?
Q 13.
	What is the life span of sea anemones? In Between Pacific Tides, Edward F. Ricketts refers to a sea anemone that allegedly lived to an age of 80 years.
Q 14.
	In my aquarium, I have several baby white anemones that budded off larger ones. Can you offer advice as to how I should feed them?
Q 15.
	Are there any dangerous species of sea anemones along the West Coast of the United States? I recently fed my sea anemone a bloodfin which it ate but, later, the anemone refused to eat a dead clownfish (anemonefish). Also, my live clownfish are unharmed when they swim among the anemone's tentacles. How do anemones tell the difference between fishes?
Q 16.
	I recently fed my sea anemone a bloodfin which it ate but, later, the anemone refused to eat a dead clownfish (anemonefish). Also, my live clownfish are unharmed when they swim among the anemone's tentacles. How do anemones tell the difference between fishes?
Q 17.
	Is there any way to preserve a sea anemone with its tentacles expanded?
Q 18.
	I collected a strawberry anemone in the Bahamas for my aquarium. How do these animals propagate?
Q 19.
	In 1974, Upjohn Chemical Company planted some gorgonians in waters off the Cayman Islands for use in its research with prostaglandins. Can you provide information about the isolation of prostaglandins from gorgonians and their use in medicine?
Q 20.
	I found this strange-looking organism washed up on the beach at Coronado, California. Can you identify it for me?
Q 21.
	While diving at a depth of 60 feet in Palancar Gardens waters off Cozumel, I noticed a sea anemone releasing a milky substance from its mouth, like smoke from a chimney. The anemone's base was swollen to the size of a baseball and its mouth was extended up through its tentacles. The "white smoke" was visible from 20 feet away. Was this part of the reproduction process, or was it an expulsion of waste materials?
Q 22.
	I've read about the cloak sea anemone, which protects a particular hermit crab by stretching itself over the shell in which the crab lives. Can you provide information about this unusual relationship?
Q 23.
	During a night dive in the Sea of Cortez of San Carlos, Mexico, I saw a sea anemone with many budlike protrusions on its stalk. Can you identify the anemone and describe the function of the buds?
Q 24.
	What do aquarium keepers at public facilities feed the beautiful sea anemones kept in the exhibit tanks?
Q 25.
	How do sea anemones feed, and what creatures do they eat?
Q 26.
	How does a sea anemone figure out when food is nearby?


_{-- a n s w e r s a b o u t S e a a n e m o n e s --}
	Q&A 1.	How do sea anemones feed?
	These flowerlike sea creatures sting and swallow fishes, sea worms, and other food. The myriad adhesive tentacles paralyze and force the food material down the sack-like gullet, where it is digested. Since sea anemones (order Actiniaria) do not possess a continuous digestive tract as in higher animals, the undigested food material must be expelled through the mouth opening.
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	Q&A 2.	Are sea fans plants or animals?
	Despite their marked resemblance to plants of some sort, sea fans (Gorgonacea) are actually colonies of animals. They are related to the corals but instead of building a limey skeleton as do the true corals, the Gorgonians construct a tough but flexible central stem remarkably resembling wood in appearance and texture. The many species of Gorgonians range from shallow reefs quite close to shore to deep sea, but are most common in the former habitat. Notably absent in the Pacific, Gorgonians are abundant in the warm waters of the Caribbean. These delicately-branched "sea fans" are especially characteristic of coral reefs, where they assume a wide variety of shapes and colors. Although they are usually purplish, their colors run through varying shades of blue, red, brown, orange, or yellow, while some are blackish.
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	Q&A 3.	Is the sea anemone an animal or a plant?
	Despite the flower-like appearance of this sea creature, it is an animal and not a plant, which it is sometimes taken for by the non-scientist. There are a vast number of sea anemone species, and a great number of them are found attached to rocks in tide pools. Along with the corals and jellyfishes, sea anemones belong to the great Phylum Coelenterata and feed on minute drifting life which they paralyze with batteries of tiny stinging cells. If a living sea anemone is touched or disrupted, it will promptly close itself up in a most unplantlike manner.
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	Q&A 4.	What is the "sea-pansy"?
	This oddly-formed relative of the corals consists of a flattened, kidney shaped fleshy pad on which there are a number of flowerlike polyps. A short fleshy rootlike structure anchors the colony in the bottom muds on which it lives, Sea pansies (Renilla) are from one to two inches in diameter and usually of a purplish or pinkish color. Their deep-sea relatives, the elongate "sea pens" are brilliantly luminous when observed at night.
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	Q&A 5.	How do sea anemones feed? Miami, Florida
	These flowerlike sea animals capture their prey by the myriad of adhesive tentacles that paralyze and force the food material down the sack-like gullet, where it is digested. Their food consists of small fishes, sea worms and other foods. As one of the members of the order Actinaria the sea anemone does not possess two ends to its digestive system, undigested food being expelled through the mouth opening.
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	Q&A 6.	I am a marine collector. I would like to know the scientific name of the "passion flower" and the general areas where it may be found. Miami, Florida
	No doubt you refer to the sea anemone Condylactes gigantea (Weinland) which is common at Miami, the Bahamas, Tortugas and various places in the West Indies. The column of this animal varies in color from bright scarlet to brownish, and the tentacles are brownish or paler than the column and usually tipped with scarlet.
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	Q&A 7.	I am interested in finding a source of information on the sea fan which is found in our waters. I have been told that Rhipidogorgia flabellum is the proper name for it, but I have been unable to find any information in either the dictionary or the Encyclopaedia Britannica. Can you help me? Ft. Lauderdale, Florida
	The proper name of the sea fan found in our waters is Gorgonia flabellum, which is sometimes called Rhipidogorgia flabellum. The sea fan is a colonial animal belonging to the phylum Coelenterata, and is closely related to the corals. It lives in the offshore reefs of southeast Florida and throughout the West Indies. More information about this animal can be found in any good text on invertebrate zoology.
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	Q&A 8.	Is there any way sea fans can be preserved, especially as to color and pliability? Ft. Lauderdale, Florida
	Immediately after bringing them ashore, sea fans should be washed for a few minutes in fresh water to remove the salt. They then should be dried in the shade. Despite everything one can do, the natural color will fade out and there is no way to keep them pliable. Brightly colored sea fans offered at souvenir shops have been dyed.
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	Q&A 9.	I have heard the Japanese use sea anemones as food. Is this true? Damariscotta, Maine
	We are unable to find any information on the use of sea anemones as food in Japan or anywhere else in the world. One of the staff members at the Institute of Marine Sciences of the University of Miami, a native Korean, reports that he has never heard of sea anemones being consumed in either Japan or Korea. After reading in the May 1962, issue of Sea Secrets that our staff was "unable to find any information on the use of sea anemones as food in Japan or anywhere else in the world," two readers have written to protest that sea anemones are eaten in at least two places--though not necessarily with relish. According to Dr. Preston E. Cloud, Jr., of the University of Minnesota, sea anemones are consumed by the Samoans, who suffer occasional fatal illness from eating improperly prepared specimens. The government hospital of Pago Pago, American Samoa can provide more detailed information, Dr. Cloud suggests. Albert Calmette (Venoms, venomous animals and activenomous serum therapeutics; London, John Bole, pp. 269-272, 1908) reports toxicity of anemones when eaten. Sea anemones seem to have a better reputation on the Mediterranean countries. Professor Enrico Tortonese of the Genoa, Italy, Museum of Natural History writes that "such animals (Actinia equina and Anemonia sulcata) have been eaten for a long time in certain regions of Italy and probably of other Mediterranean countries. The ancient Roman writer Apicius gave instructions for preparing (sea anemones) in the kitchen. "They are fried or boiled," Professor Tortonese relates, "preferably in sea water, and I have been told they are quite good. For a bibliographical reference see G. Cavanna, Doni di Nettuno (Gifts of Neptune; Florence, 1913), page 173."
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	Q&A 10.	Can a sea anemone be kept in a home aquarium? Can fishes or other forms of marine life be kept with it? Belle Rose, New York
	Solitary sea anemones can be kept in small marine aquaria very successfully. In fact, some of the longest records of longevity among invertebrates were established by sea anemones kept in small aquaria. They may live fifty years or more. Very few animals prey upon sea anemones, which are predatory animals. Small fishes placed with them will most certainly be eaten.
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	Q&A 11.	Diving off the island of Tobago, I observed a West Indian fighting conch, the shell of which was covered by a bright red thready growth. We were at 90 feet, below the level of red light penetration. The growth had the appearance of red propylene rope threads, and the color was very bright, resembling the warning red paint used on an aircraft. Do you have any idea what this might be? Tobago, West Indies
	Without seeing the fluorescent substance you describe on the conch shell, it is not possible to say for certain what it is. However, some of the sea anemones are known to fluoresce. Members of the genus Calliactis furthermore, emit threadlike defensive substances which reportedly fluoresce very much in the manner you describe. Frequently a number of individuals of this sort of anemone will attach to one shell, preferring one inhabited by a hermit crab.
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	Q&A 12.	Can you identify this animal which I have found in the surf off Cocoa Beach, and have preserved in formalin? Titusville, Florida
	The sea animal that you sent to us is the sea pansy, Renilla reniformis. It is an alcyonarian (or octocoral) belonging to the class Anthozoa of the phylum Coelenterata, and is closely related to the sea fans and sea whips. The name sea pansy was derived from the animal's flattened kidney-shaped pad, on which there are flower-like polyps, and its violet color; however, some sea pansies have a rose, purplish white or yellow tint, and are heart shaped. A short fleshy stalk anchors the sea pansy to the sea bottom, and they sometimes occur by the hundreds in a muddy bay. They are found along the southeast coast of the United States from Cape Hatteras to Florida, and in the Antilles and along the east coast of South America. Sea pansies sting their prey and entangle it in a mucous net. Further information can be obtained by reference to The Invertebrates: Protozoa through Ctenophora by L.H. Hyman (McGraw-Hill Book Company, New York, 1940), and The Shallow-Water Octocorallia of the West Indian Region by F.M. Bayer (Martinus Nijhoff, The Hague, Netherlands, 1961).
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	Q&A 13.	What is the life span of sea anemones? In Between Pacific Tides, Edward F. Ricketts refers to a sea anemone that allegedly lived to an age of 80 years. Balboa, Canal Zone
	Sea anemones have often been reported to have long life spans, but most of these reports have been undocumented or from older literature. In The World of the Sea, translated and enlarged by H.M. Hart (Cassell, Petter and Galpin, London, 1873), it was reported that Dalyell kept a specimen of Actinia mesembryanthemun alive for 20 years and, in The Biology of the Seashore (Sidgwick & Jackson, Ltd., London, 1922), Flattely and Walton report that Dalyell kept this anemone for 60 years. In the reference you mention, there appears to be no documented evidence that the anemones lived for more than 30 years. In The Invertebrates, Vol. 1 (McGraw-Hill Book Company, New York, 1940) Hyman states that some anemones live at least 50 years and probably even longer, and this seems to be a reasonable estimate.
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	Q&A 14.	In my aquarium, I have several baby white anemones that budded off larger ones. Can you offer advice as to how I should feed them? Huntington Beach, California
	Regardless of age, healthy sea anemones should respond to food placed with an eyedropper or by hand on their tentacles. The best type of food depends on the type of anemone. Those with short, thick tentacles, which are "sticky" when touched, should be fed pieces of meat or fish. Those with long slender tentacles usually feed primarily on plankton and, therefore, can be fed either live or frozen brine shrimp. In either case, a small feeding twice weekly is ideal although a healthy anemone can go several weeks without food. If the animals do not respond to food placed on their tentacles, this may indicate either that they are satiated or are unhealthy. As a last resort, you may try forcing ground shrimp or fish down the gullet of each one with an eyedropper. Further information can be found in Sea Anemones by U. Erich Friese (T.F.H. Publications, Neptune, New Jersey, 1973).
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	Q&A 15.	Are there any dangerous species of sea anemones along the West Coast of the United States? Philomath, Oregon
	No. The sea anemones that are known to have the stinging power to affect man adversely are found in parts of the Arctic, North Atlantic, and western South Pacific oceans. Examples are Lebrunia danae, a common species in the Florida Keys and Caribbean; Anemonia sulcata and Adamsia palliata, which occur from Norway to the Mediterranean Sea; Sagartia elegans, commonly known as the rosy anemone, which is found in Iceland to the Mediterranean; and Actinia equina, which inhabits the eastern Atlantic from the Arctic to the Gulf of Guinea, as well as the Mediterranean, Black, and Azov seas. The most venomous species appears to be Dofleina armata, which occurs in waters off the west coast of Australia (see "Anonymous Anemone," Sea Frontiers, Vol. 18, No. 6, November-December, 1972). Sea anemones catch food with their tentacles which, as described in the above-mentioned article, "possess various-sized batteries of stinging organs, or nematocysts. These capsules react when touched by shooting hundreds of microscopic stingers into the flesh of the victim. The poison injected by these stingers paralyzes the prey..." Thus, if a diver brushes against of touches the tentacles of an anemone possessing a high degree of stinging power, he is liable to activate hundreds of minute stinging organs and suffer painful injury.
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	Q&A 16.	I recently fed my sea anemone a bloodfin which it ate but, later, the anemone refused to eat a dead clownfish (anemonefish). Also, my live clownfish are unharmed when they swim among the anemone's tentacles. How do anemones tell the difference between fishes? Fairfield, New Jersey
	The mechanism by which anemonefishes are rendered immune to the sting of their anemone host has long been studied. The general opinion is that the immunity factor, a chemical that inhibits triggering of the anemone's feeding response, occurs in the slimy coating of the fish. The bloodfin, lacking this chemical, was eaten. A freshly dead anemonefish, however, would still possess the chemical and thus be rejected. This can be demonstrated quite easily. If another anemonefish in the aquarium dies, carefully wipe off all its mucous coating and offer it to the anemone. It is likely that there will be a complete change in the behavior of the anemone, and it will accept the fish. Further information is given in Anemonefishes by G. Allen (Tropical Fish Hobbyist, Inc., Jersey City, New Jersey, 1972), which is available at most pet stores. A more technical source of information is "Observations on the Symbiosis of the Sea Anemone Stoichactis and the Pomacentrid Fish Amphiprion percula" by Davenport and Norris (Biological Bulletin, 115:397-410).
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	Q&A 17.	Is there any way to preserve a sea anemone with its tentacles expanded? Seattle, Washington
	In order to relax live marine invertebrates before preserving them, a 3.5-percent solution of magnesium chloride or magnesium sulfate may be administered in small amounts, until the animal no longer responds to stimuli that would ordinarily cause it to contract. The cheapest solution uses Epsom salts instead of more expensive, pure magnesium salts. A 3.5-percent solution has the same salinity as seawater (35 parts per thousand), and its addition to the water surrounding the animal causes no osmotic problems. The amount of solution required to relax an anemone depends on the species and size just as it does among other groups of invertebrates. Some animals will relax in a few minutes after the addition of a small amount of solution, while others may take hours. If the addition of the solution causes the anemone to contract, no more should be added until it expands again (sometimes a period of hours). Considerable experimentation may be required before desirable results are attained. Sometimes other chemicals, such as propylene phenoxetol or chloral hydrate (available only by prescription), are used for relaxing invertebrates, but the first is the most commonly used and safest method.
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	Q&A 18.	I collected a strawberry anemone in the Bahamas for my aquarium. How do these animals propagate? Chaumont, New York
	Common names for organisms are often misleading, since two entirely different organisms may be called by the same common name. The strawberry anemone is assumed to be the small, often reddish-maroon anemone, Actinia bermudensis. This species is capable of both asexual and sexual reproduction. Asexually, the anemone simply splits longitudinally by fission. In sexual reproduction, for anemones in general, the eggs are fertilized either internally or externally, depending on the species. The fertilized egg then develops into a free-swimming planula larva, which later passes into an Edwardsia stage, so called because of the larva's resemblance at this time to the anemone genus Edwarsia. It is during this stage that the anemone settles and begins to assume the characteristics of the adult form.
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	Q&A 19.	In 1974, Upjohn Chemical Company planted some gorgonians in waters off the Cayman Islands for use in its research with prostaglandins. Can you provide information about the isolation of prostaglandins from gorgonians and their use in medicine? Yuba City, California
	Prostaglandins are natural human hormones. They are also found in certain species of gorgonians, or soft corals--in particular, Plexaura homomalla. When prostaglandins were first being studied by pharmaceutical companies for use in medicine, research was facilitated by their isolation from this gorgonian. For several years, Upjohn Chemical Company did collect gorgonians to extract chemicals for medications. Since the time (1970's), chemical synthetic techniques have been developed to allow the synthesis of prostaglandins. Some European pharmaceutical companies may still collect gorgonians, but laboratory-synthesized drugs are generally preferred, since their structures are always the same. The effect or purpose of prostaglandins in gorgonians is not known, but is thought to be a chemical defense. Prostaglandins are a large family of similarly structured chemicals that have hormonal effects in mammals, generally acting on smooth muscle. Currently, they are being studied for possible use as antiasthma and antitumor agents.
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	Q&A 20.	I found this strange-looking organism washed up on the beach at Coronado, California. Can you identify it for me? San Diego, California
	The brown animal you found is the sea pansy Renilla kollikeri. When it is alive, this species is purple. Sea pansies (Renilla spp.) are members of the class Anthozoa, which includes corals and sea anemones. The only anthozoans that anchor in soft sediment, these colonial animals consist of a flat spongy disk known as a rachis and a stalk called a peduncle. The peduncle extends down into the sandy sea bottom, and it is believed that its tip expands, thereby serving as an anchor. The upper surface of the rachis, which in R. kollikeri can grow to 3 inches in diameter, is studded with two kinds of flowerlike polyps named autozooids and siphonozooids. The larger of the two kinds--the autozooids--have eight tentacles and occur singly. Responsible for capturing microzooplankton, the tentacles can retract into the rachis. The smaller siphonozooids occur in clusters. A modified polyp form, they act as intake pores for the circulation of seawater through the rachis and peduncle. Sea pansies move through the sediment by contraction of the rachis and peduncle. R. kollikeri is preyed upon by the nudibranch Armina californica and the starfish Astropecten armatus. During an attack by a predator, waves of bioluminescence radiate across the sea pansy's rachis from any point of stimulation.
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	Q&A 21.	While diving at a depth of 60 feet in Palancar Gardens waters off Cozumel, I noticed a sea anemone releasing a milky substance from its mouth, like smoke from a chimney. The anemone's base was swollen to the size of a baseball and its mouth was extended up through its tentacles. The "white smoke" was visible from 20 feet away. Was this part of the reproduction process, or was it an expulsion of waste materials? New Orleans, Louisiana
	The "white smoke" you observed probably was sperm. Most sea anemones aren't very mobile; therefore, they most release sperm and, in some species, eggs into the seawater in order to reproduce. A few species of anemones are reported to release sperm through the tips of their tentacles or pores in the body wall, but most release sperm and eggs through their mouths. Sperm usually look milky or cloudy, and eggs look like very small particles or dots. A diver making careful observations should be able to tell the difference. In most sea anemones, the sexes are separate, and fertilization is either external or internal. During external fertilization, the sperm and eggs combine the seawater. During internal fertilization, sperm carried by water currents enter a female's mouth where they combine with eggs. A free-swimming planula larva or small juvenile is later released through the mouth. Sea anemones also reproduce asexually via pedal laceration, longitudinal fission, transverse fission, or budding. In pedal laceration, small bits of the pedal disk, where the anemone is attached to the bottom, pinch off and grow into new animals. In longitudinal fission, the anemone splits in two. The plane of fission is parallel to the animal's long axis running from its mouth to its foot. In transverse fission, the top part of the sea anemone pinches off. In budding, tentacles pinch off and develop into new animals.
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	Q&A 22.	I've read about the cloak sea anemone, which protects a particular hermit crab by stretching itself over the shell in which the crab lives. Can you provide information about this unusual relationship? Long Beach, California
	The cloak sea anemone (Adamsia palliata) lives in waters off the Atlantic coast of Europe and in the Mediterranean Sea. It has an intimate and somewhat bizarre association with the hermit crab (Eupaguras prideauxi). When young, E. prideauxi creeps along rocky or sandy bottoms searching not only for an empty snail shell to live in, but for a cloak anemone as well. Once it finds a shell, the crab uses its claws and legs to detach the anemone from the bottom. The crab then positions the anemone so that it can envelope the shell with its base. As the hermit crab grows, the cloak anemone secretes a horny membrane that extends out from the shell lip. This addition allows the crab to use the shell longer. The crab eventually discards the shell and lives within the horny cloak made by the anemone. The anemone's stinging tentacles also protect the hermit crab from predators; the crab is immune to the venom in the tentacles. The anemone in turn benefits by eating the crab's leftovers. To do so, it distends its body and feeding tentacles in order to pick up fallen food particles from the sea bottom.
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	Q&A 23.	During a night dive in the Sea of Cortez of San Carlos, Mexico, I saw a sea anemone with many budlike protrusions on its stalk. Can you identify the anemone and describe the function of the buds? Peoria, Illinois
	The sea anemone you saw in the Gulf of California probably was the sand anemone (Alicia beebei). At night, the anemone spreads its crown of tentacles and expands its stalk decorated with numerous distinct outgrowths called pseudotentacles. During the day, the tentacles and the stalk contract, and the animal looks like a mass of clustered berries. Hence, many people who see this animal during the day don't recognize it as an anemone. Other members of the family Aliciidae, such as the berried anemone (Alicia mirabilis, right), also bear pseudotentacles on their stalks. Pseudotentacles usually have stinging cells (nematocysts) similar to those in the tentacles. The function of the nematocysts differ, however. In pseudotentacles, they are used in defense, while in the crown tentacles, they capture food. Pseudotentacles may be highly branched and loaded with algal cells called zooxanthellae. In one anemone, Lebrunia coralligens, the diurnal expansion and contraction of the two types of tentacles may be related to the feeding habits of the animal. During the day, the pseudotentacles are exposed to light and the algal cells photosynthesize. At night, the tentacles expand and the animal feeds on particles in the water.
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	Q&A 24.	What do aquarium keepers at public facilities feed the beautiful sea anemones kept in the exhibit tanks? Islip, New York
	We checked with aquarists at the Miami Seaquarium (Florida) and found that they pour brine shrimp, thawed after being frozen, into the sea anemone display tanks. The tiny brine shrimp are moved around in the tank by the water currents, and the anemones catch them on their tentacles. Excess brine shrimp gradually wash out of the tank as the water flushes through the system. Large anemones may also be fed chunks of fish or commercial shrimp. These larger pieces of food, which won't be stirred up by the water currents, are hand-fed to the anemones. This ensures that every anemone receives some food, and that none is left on the tank bottom to spoil. Hand-feeding is more labor intensive than just adding brine shrimp to the water, so fish and commercial shrimp may only constitute part of the captive anemone's diets.
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	Q&A 25.	How do sea anemones feed, and what creatures do they eat? New York, New York
	Sea anemones catch prey with their tentacles, which then move suitable food items to the mouth. Depending on the species, eight to several hundred tentacles ring the mouth located at the top of the column-shaped anemones. The mouth, slitlike when closed, often gapes open when these animals feed. Anemone tentacles are studded with stinging cells called nematocysts. Each nematocyst contains a harpoonlike thread that is everted when the tentacle contracts something. Many nematocysts are fired into each food item, snaring and poisoning the catch. Once inside the mouth, food items move to the bottom of the saclike gastrovascular cavity where digestion occurs. This cavity is divided longitudinally by radiating mesenteries and filaments. The free edges of these structures produce the enzymes necessary for extracellular digestion of proteins and fats, and also are where absorption and intracellular digestion occur. Because the gut of the sea anemones is a simple sac, undigested food and wastes are expelled through the mouth. Most sea anemones feed on invertebrates, such as small crustaceans, marine worms, zooplankton, and other waterbourne particles. Large sea anemones also swallow crabs, clams and small fishes.
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	Q&A 26.	How does a sea anemone figure out when food is nearby? Little Rock, Arkansas
	The microscopic hair bundles on a sea anemone's tentacles respond to vibrations caused by prey such as planktonic shrimp, says Glen Watson of the University of Southwestern Louisiana. In the absence of the prey, these bundles, which are vibration sensitive mechanoreceptors like those of human ears are tuned to a frequency of 55-hertz vibration caused by a tiny approaching shrimp. Once a shrimp does swim near an anemone, says Watson, acidic sugars from its surface bind to chemoreceptors on the anemone's tentacles. This binding causes the hair bundles to elongate, and they respond to lower frequencies coinciding with those the prey produces when it swims. It's as if the anemone can only "hear" the prey after it "smells" it, says Watson. The anemone's fine-tuning of frequencies paves the way for controlled attack. It fires its valuable stinging cells (nematocysts) only when a prey item--generally a small invertebrate--is close to it. After poisoning the catch, the anemone's tentacles move the food to the mouth, which gapes during an attack. A sea anemone knows food is near when its chemical receptors tell its mechanical sensors to tune into the prey's low frequency vibrations.
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