Anthozoa (Anemones and Corals)

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Anthozoa

(Anemones and corals)

Phylum Cnidaria

Class Anthozoa

Number of families 130

Thumbnail description
Exclusively polypoid cnidarians. Tubular body with hollow tentacles around the mouth; has a pharynx that opens into a digestive cavity subdivided by infoldings of the gut wall. May be solitary or colonial, with or without an internal or external skeleton.

Evolution and systematics

Anthozoa is the largest class in the phylum Cnidaria, with over 6,000 extant species divided among nine orders and classified in two subclasses. The nine orders are as follows:

Subclass Octocorallia (= Alcyonaria)

Order Pennatulacea, the sea pens and sea pansies; 16 families
Order Helioporacea, the blue corals; two families
Order Alcyonacea, the soft corals, sea fans, and sea whips; 29 families

Subclass Hexacorallia (= Zoantharia)

Order Actiniaria, the sea anemones; 42 families
Order Scleractinia (= Madreporaria), the true (stony or hard) corals; 25 families
Order Corallimorpharia, the mushroom (false) corals (also known as mushroom anemones or disc anemones); 4 families
Order Zoanthidea (= Zoanthinaria), the zoanthids; four families
Order Antipatharia, the black (thorny) corals and wire corals; five families
Order Ceriantharia, the tube anemones; three families

Some authors classify the Ceriantharia and Antipatharia together in a third subclass, the Ceriantipatharia, but genetic evidence does not support this grouping.

Molecular evidence places the Anthozoa as the earliest branch of the phylum Cnidaria. Since anthozoans exist exclusively as benthic (sea bottom) polyps, whereas the remaining cnidarians have life cycles that alternate between benthic polyp and pelagic medusoid stages, this evidence indicates that the polyp stage is the ancestral condition among Cnidaria. Within the Hexacorallia, additional evidence suggests that actiniarians, and more recently corallimorpharians, may have evolved from a scleractinian ancestor, accompanied by the loss of a skeleton.

Fossils resembling anthozoans, including sea pens, are known from as early as the Precambrian eon (>540 million years ago [mya]), but it wasn't until the Ordovician period (about 465 mya) that stony coral fossils became common. Two groups of corals dominant among Ordovician fossils—the Tabulata and Rugosa—became extinct at the end of the Permian period (about 248 mya). The earliest scleractinian fossils come from the middle Triassic period (about 230 mya).

Physical characteristics

Anthozoans are polypoid cnidarians. As in all cnidarians, the body wall is composed of two cell layers—the outer ectodermis (or epidermis) and the inner gastrodermis—separated by a layer of gelatinous material known as mesoglea or mesenchyme. Tentacles bearing stinging cells surround the mouth, which is the only opening to the digestive system. A polyp is essentially a tubular sac, with the mouth and tentacles on a flattened upper surface called the oral disk. The mouth leads to a pharynx, a short tube projecting into the closed gut (the coelenteron or gastrovascular cavity). The pharynx typically has one or more ciliated grooves (siphonoglyphs) that funnel water into the coelenteron. The coelenteron is subdivided into chambers by vertical septa (or mesenteries), infoldings of the gut wall that may or may not

attach to the pharynx. Below the pharynx, the free edges of the septa are thickened to form septal, or mesenterial, filaments that contain cells involved in digestion, including nematocysts. The tentacles are hollow and continuous with the coelenteron.

Octocorals have eight pinnate (parts arranged on each side of a common axis) tentacles and eight septa; hexacorals have septa and tentacles—usually simple—in multiples of six. Cerianthids have two circlets of tentacles, one around the mouth and the other around the edge of the oral disc. There are a number of other details of polyp anatomy that are used to distinguish the orders of Anthozoa.

A unique characteristic of cnidarians is the cnida, a complex intracellular capsule containing an eversible hollow tubule that can be released to sting or trap prey. Eversible means that the structure can turn inside out. There are three basic types of cnidae, and all can be found in the class Anthozoa. Nematocysts, which contain toxins and are typically armed with spines for penetrating the tissues of other organisms, are possessed by all anthozoans. Spirocysts are sticky rather than penetrating and are found only in the hexacorallians. Ptychocysts are unique to the cerianthid tube anemones and are used to construct their tubes.

Species in the orders Scleractinia, Octocorallia, and Antipatharia produce skeletons. In the Scleractinia, the living tissue essentially lies above an external skeleton made of calcium carbonate secreted by the ectodermis. Scleractinian skeletons can take on a variety of shapes, generally described as massive, columnar, encrusting, branching, leaflike or platelike. It is these skeletons that form the framework of tropical coral reefs. Antipatharians secrete an internal horny skeleton that is flexible, black in color, and equipped with thorns on its surface. Octocorals secrete an internal skeleton composed of a protein called gorgonin, calcium carbonate, or a combination of both. Octocorallian and antipatharian skeletons are usually branching treelike or whiplike forms. Unlike other octocorals, helioporaceans produce a massive skeleton that is blue in color and resembles those found in the stony corals. Octocorals

also secrete small calcareous sclerites (hardened plates) of a variety of shapes and colors that are embedded in the mesenchyme and that may give a spiny or scaly appearance to the colony. Octocorallian soft corals lack a supporting internal skeleton and can inflate or deflate the fleshy colony by funneling water into or out of their polyps. With the exception of the zoanthid genus Gerardia, species in the remaining anthozoan orders do not secrete a skeleton. A few actiniarians secrete a chitinous tube, and one genus is able to form a chitinous coiled shell, similar in shape to a snail shell, that is inhabited by a hermit crab. Cerianthids build soft, felt-like tubes from fired ptychocysts.

Anthozoans may be either solitary or colonial. In colonial species, the polyps are united by living tissue, the coenenchyme, and their gastrovascular cavities are joined by canals or tubes. Actiniarians and ceriantharians are exclusively solitary, and the octocorals and antipatharians are exclusively colonial, but the remaining orders have both types of morphologies. Solitary polyps are commonly 0.5–2 in (1–5 cm) in diameter at the oral disk, but the largest species grow to 3 ft (1 m) across. Polyps of colonial species are typically much smaller (<0.4 in (5 mm)), but the colonies themselves can be quite large. Octocorallian and antipatharian colonies may grow >8 ft (2.5 m) tall, and some scleractinian corals may reach a size of 19.5 ft (6 m) in height and width. Colonial anthozoans may reach a great age. For example, many octocorals are 100 or more years old, and the deep-sea zoanthid Gerardia has been estimated to be 1800 years old.

Distribution

Anthozoans are found worldwide in all oceans.

Habitat

Anthozoans are restricted to marine habitats, but can be found from the intertidal zone to over 19,500 ft (6,000 m) deep. Solitary forms may be attached to a hard substrate or burrowed into soft bottom mud or sand. Colonial forms grow as an encrusting or stoloniferous form on other substrates, or build massive skeletons; tree-like colonial forms are attached by the base of the main stem. Sea pen colonies are anchored into soft bottoms by the base of the primary polyp. Reef-building corals are most typically found in clear, shallow, warm tropical waters, although a few species are known from the cold, dark deep sea.

Behavior

One of the most spectacular of anthozoan behaviors is the synchronous release of sperm and eggs by many colonies over a wide area of coral reef. Mass spawning events have been observed in octocorallian and zoanthid species, but are best known in the scleractinian corals of the Great Barrier Reef, Australia. In some cases, many species release gametes on the same night, and there is considerable evidence that hybridization between species may occur. Synchrony is achieved by timing gamete release with the lunar cycle, and many corals spawn shortly after sunset following a full moon. Eggs and sperm may be released separately into the water column; or, in some hermaphroditic species, may be combined into gamete bundles that float to the surface and break apart there. During these mass spawning events, huge slicks of gametes and developing larvae can be observed on the water surface, attracting a variety of predators that feed on the spawned gametes.

Anthozoans engage in aggressive interactions to defend space from neighboring individuals of the same or different species. A number of specialized structures may be used to repel encroachers. Sea anemones may possess acrorhagi, inflated saclike structures bearing nematocysts that ring the collar below the tentacles. Acrorhagi can be elongated to come into contact with an intruder, whereupon they cause tissue death. Scleractinian, octocorallian, and antipatharian corals may develop specialized tentacles ("sweeper tentacles") after prolonged contact with foreign species. These tentacles are five to ten times longer than normal feeding tentacles and have a greater number of stinging nematocysts. The tentacles search and sweep an area around the polyp and cause tissue death in neighboring species upon contact. Similar structures found in some sea anemones are called "catch tentacles." Some scleractinian corals and corallimorpharians also may extrude their septal filaments to digest the neighboring species' tissues.

Several octocorallian species can produce light when contact with the colony is made. This bioluminescence may be in the form of a bright green flash from a polyp, or a wave of light across the colony as polyps flash sequentially from the point of contact. It is likely the light is meant to startle visual predators.

Feeding ecology and diet

Most anthozoans are suspension feeders whose diet consists of small planktonic invertebrates, phytoplankton, bacterio-plankton, or other suspended organic matter. Their methods of prey capture are generally, though not exclusively, passive. Drifting prey may be captured when it comes in contact with the extended tentacles of anthozoan polyps. Prey capture may also involve the firing of cnidae. Many scleractinians produce a slimy mucus that covers the polyp and traps floating and sinking food particles. The mucus is moved around by cilia (small hairlike projections), and eventually enters the mouth. Large sea anemones may feed on crabs, bivalves and fishes, while ptychodactarian anemones have been observed preying upon gorgonian octocorals. In 1997, colonies of the soft coral Gersemia antarctica were first reported to bend over and feed in the soft sediments of the Antarctic. Researchers proposed that this feeding strategy may be employed where suspended organic material is in low supply, as it is in the deep sea. Some anthozoans also may absorb dissolved organic matter directly from the seawater into their cells.

Another source of nutrition for many anthozoans comes from symbiotic photosynthetic algae living within cells of the gastrodermis. Like other plants, these algae produce energy-rich organic molecules through photosynthesis; between 20% and 95% of this production is transferred to the host. These

symbionts are usually dinoflagellates, called "zooxanthellae"; however, green algae symbionts ("zoochlorellae") are also known. Most shallow-water, reef-building corals contain zooxanthellae, and they also may be found in tropical gorgonians, anemones, and zoanthids. The zooxanthellae are additionally thought to increase the rate at which scleractinian reef corals produce their calcium carbonate skeleton.

The predators of anthozoans include nudibranchs, sea stars, crabs, polychaetes, and fishes.

Reproductive biology

Anthozoans display a wide range of reproductive strategies. Asexual clones may be produced in a variety of ways. Polyps may undergo fission in either a longitudinal or transverse direction. Many sea anemones produce clones by pedal laceration, wherein pieces of the pedal disk tear off or break free and develop into new individuals. The growth of anthozoan colonies may be considered a mode of asexual reproduction. After a free-living larva settles, it metamorphoses into a polyp that repeatedly divides to give rise to additional polyps, all of which remain connected by living tissue. In some species, budded polyps may be released from the parent colony, and these then settle and develop a new colony. Anthozoans, particularly colonial species, also may reproduce by fragmentation. For many scleractinian corals, damage caused by storms or strong wave action may produce fragments that lead to new colonies.

Anthozoans may be gonochoristic (having separate sexes) or hermaphroditic. In colonial species, gonochoristic colonies are composed entirely of male or female polyps, whereas hermaphroditic colonies may have both male and female polyps ("monoecious") or hermaphroditic polyps. Polyps lack well-defined gonads; rather, the gametes accumulate in the gastrodermis of some or all mesenteries. The gametes are typically shed into the gastrovascular cavity and are either released through the mouth for external fertilization ("broadcast spawners"), or eggs are retained for internal fertilization and the embryos released through the mouth at a later time ("brooders"). Brooding species may hold the embryos internally within the gastrovascular cavity or externally in a coat of mucus on the polyp's surface. Anthozoan embryos develop into ciliated planula larvae that may or may not feed, and that can stay in the water column for days to weeks. Contrary to initial assumptions, some species also can produce larvae asexually.

Conservation status

Some of the largest concentrations of anthozoans, in terms of both numbers and species diversity, occur on coral reefs. Such human activities as fishing, coastal development, terrestrial runoff, and marine pollution have had dramatic negative impacts on coral reefs, as have coral diseases that have increased in frequency and severity over the last decade of the twentieth century. Despite a ban in most countries, cyanide is still commonly used to collect reef fishes for the aquarium trade. The cyanide stuns the target fishes, allowing for easy collection, but kills many of the anthozoans and other invertebrates living on the reef. In 1998, the World Resources Institute estimated that more than half of the world's coral reefs are threatened by these and other human activities. As of 2002, however, only two anthozoan species were listed on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species: the broad sea fan, Eunicella verrucosa, and the starlet sea anemone, Nematostella vectensis. All scleractinian corals, antipatharian black corals, and octocorallian blue corals and organ-pipe corals, are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). This listing means that "trade must be controlled in order to avoid utilization incompatible with their survival." A number of other treaties have been established to protect coral reef organisms, such as the International Coral Reef Initiative and the U.S. Coral Reef Initiative. Most recently, there has been concern over the impact of deep-sea fisheries trawling on slow-growing deep-water corals. Norway and Australia have created conservation areas to protect reefs within their territorial waters.

Significance to humans

Coral reefs, which are largely a framework of scleractinian skeletons glued together by sponges and other organisms, are a major tourist destination and source of recreation. Corals provide a habitat for a variety of organisms that humans use for food, including fishes, urchins, mollusks and crustaceans. It is estimated that approximately 50% of U.S. federally-managed fisheries depend on coral reefs for part of their life cycle, at an annual worth of over $100 million. Anthozoans of all orders (except Antipatharia) are sold in the aquarium trade, and octocorallian and antipatharian skeletons are used to make coral jewelry. Scleractinian skeletons are used as building material and in bone grafts, as the structure of the coral skeleton is similar to that of human bone. Black

coral skeleton was once thought to have medicinal properties, and the name "Antipathes" is a Latin word that means "against disease." A variety of natural products have been isolated from anthozoans for commercial use, from suntan lotions to antifoulants. In particular, octocorals produce a range of bioactive compounds; some of these have been harvested for molecular biological and pharmaceutical applications, including anticancer and anti-inflammatory agents.

Species accounts

List of Species

Giant green anemone
Starlet sea anemone
Frilled anemone
Magnificent sea anemone
Red coral
Red soft tree coral
Black coral
American tube dwelling anemone
Elephant ear polyps
Sea pansy
Acropora millepora
Elkhorn coral
Deep water reef coral
Goniastrea aspera
Mushroom coral
Cauliflower coral
Rubber coral

Giant green anemone

Anthopleura xanthogrammica

order

Actiniaria

family

Actiniidae

taxonomy

Actinia xanthogrammica Brandt, 1835, Sitka, Alaska, United States.

other common names

Portuguese: Anémona-verde-gigante.

physical characteristics

Large, flat oral disk up to 9.8 in (25 cm) diameter; column densely covered with hollow adhesive wartlike protuberances known as verrucae; tentacles and disk are emerald green, column is olive or brownish.

distribution

Western coast of North America from Alaska south to Baja California.

habitat

Low intertidal to shallow subtidal zones on exposed coastlines where it is subject to strong wave action; it often forms carpets of individuals in surge channels.

behavior

Nothing is known.

feeding ecology and diet

Feeds on sea urchins, crabs, and mussels dislodged by floating debris. One study found that A. xanthogrammica benefits when urchins fleeing from predatory seastars fall into the anemone's tentacles. Mussels that are detached by wave action also are eaten. Also derives nutrition from symbiotic association with zooxanthellae and zoochlorellae.

reproductive biology

Gonochoristic; reaches sexual maturity in 5–10 years; planktotrophic larvae feed on algae. No asexual reproduction known.

conservation status

Not listed by IUCN.

significance to humans

Produces toxins known as anthopleurins that stimulate heart muscle and that were considered for medical use.

Starlet sea anemone

Nematostella vectensis

order

Actiniaria

family

Edwardsiidae

taxonomy

Nematostella vectensis Stephenson, 1935, Isle of Wight, England.

other common names

English: Athenarian burrowing anemone; dwarf mud anemone.

physical characteristics

Tiny worm-like anemone, rarely more than 0.6 in (15 mm) in length, with 9–18 relatively long (up to 0.4 in [10 mm]) tentacles arranged in two rings; column is smooth with a rounded base called a physa; largely translucent with white bands on the tentacles.

distribution

Atlantic and Pacific coasts of North America; southern and eastern coasts of England. It is thought to have been introduced to England from North America.

habitat

Intertidal to shallow subtidal zones; burrows in mud of estuaries and salt marshes. Tolerates a broad range of salinities (8.96–51.54 ppt) and temperatures (30 to 82°F [-1 to 28°C]).

behavior

When disturbed, the anemone can completely withdraw into its burrow. It may also move completely out of the burrow and climb onto algae and aquatic vegetation.

feeding ecology and diet

Feeds mainly on snails; however, copepods, ostracods, insects, and nematodes also have been found in the coelenteron.

reproductive biology

Gonochoristic, broadcast spawner; females release gelatinous egg masses that contain as few as five or as many as 2000 ova and hundreds to thousands of nematosomes, which are spherical, flagellated bodies containing nematocysts and are unique to this species. Planktotrophic larvae may settle in 7 days. Asexual reproduction may be more common than sexual reproduction. Several unisex populations have been discovered in North America, while no males have been observed in England. The starlet sea anemone is one of only five anemone species known to reproduce asexually by transverse fission and is the only anemone known to release gelatinous masses of eggs.

conservation status

Although as many as five million individuals have been found in a single pond, this species is listed as vulnerable on the IUCN Red List. It is considered rare and endangered in the United Kingdom, largely because of its restricted habitat.

significance to humans

Used in laboratory studies of developmental genetics.

Frilled anemone

Metridium senile

order

Actiniaria

family

Metridiidae

taxonomy

Priapus senilis Linnaeus, 1761, Baltic Sea.

other common names

English: Plumose anemone (Britain); French: Anémone plumeuse; German: Seenelke; Norwegian: Sjønellik.

physical characteristics

Tall, to 11.8 in (30 cm), with hundreds to thousands of small, slender tentacles on a lobed crown giving a feathery or plume-like appearance; column smooth with a distinct collar below tentacles; with numerous threadlike acontia arising from bases of septa that can be discharged through column pores known as cinclides; color varies from white to brownish-orange.

distribution

Circumpolar, boreo-Arctic; found as far south as New Jersey, United States, in the western Atlantic; Bay of Biscay in the eastern Atlantic; southern California, United States, in the eastern Pacific; and South Korea in the western Pacific. Introduced populations have been found in South Africa and the Adriatic Sea.

habitat

Attached to rock, shell, wood, and other hard substrates from the intertidal zone to 540 ft (166 m) deep; tolerates temperatures between 32–80°F (0–27°C).

behavior

Adjusts the length of the body column according to current flow. Uses catch tentacles equipped with specialized nematocysts to attack other species in competition for space; tips of the catch tentacles remain attached to the victim.

feeding ecology and diet

Passive suspension feeder that traps prey in mucus-coated tentacles; these particles are carried to the mouth by ciliary action.

Prey items include copepods and polychaetes; and decapod, bivalve, and gastropod larvae.

reproductive biology

Gonochoristic, broadcast spawner; planktotrophic larvae feed primarily on dinoflagellates, but also on copepods, chaetognaths and other cnidarian larvae. Asexual reproduction by pedal laceration and fission.

conservation status

Not listed by the IUCN or CITES.

significance to humans

None known.

Magnificent sea anemone

Heteractis magnifica

order

Actiniaria

family

Stichodactylidae

taxonomy

Actinia magnifica Quoy and Gaimard, 1833, Vanikoro, Santa Cruz Islands, New Hebrides.

other common names

English: Bulb-tip anemone, maroon anemone, Ritteri anemone; German: Prachtanemone; Local dialects: Ramburambu (Indonesia), Burin (Malaysia)

physical characteristics

Oral disc up to 39 in (1 m) in diameter; column as much as 8 in (20 cm) tall and wide at the base; tentacles 3 in (7.5 cm) long, of uniform thickness with blunt or slightly bulbous tips. Brightly colored column may be avocado green, magenta, cerulean blue, or white, with yellow, green, or white tentacles.

distribution

Tropical Indo-Pacific seas.

habitat

From less than 3–65 ft (1–20 m) deep on or near coral reefs, often perched on prominent structures in strong currents.

behavior

Host to clownfish (Amphiprion) and damselfish (Dascyllus) that chase off potential predators. The fishes are protected from their predators by the anemone's nematocysts, but are themselves unaffected because of a coating of mucus that they pick up from the anemone.

feeding ecology and diet

Feeds on plankton that it traps from the water using nematocysts and mucus on the oral disc; digestion of prey begins prior to ingestion. Also derives nutrition from symbiotic zooxanthellae harbored within cells lining the inside of the tentacles and oral disc.

reproductive biology

Capable of asexual reproduction by longitudinal fission. Sexual reproduction is presumed but data are lacking.

conservation status

Not listed by the IUCN or CITES.

significance to humans

Reportedly one of the most frequently photographed anemones because of its coloration, shallow-water location, and tolerance of disturbance. Sold in the aquarium trade.

Red coral

Corallium rubrum

order

Alcyonacea

family

Coralliidae

taxonomy

Madrepora rubra Linnaeus, 1758, "Mari Numidico ad la Calle".

other common names

English: Precious coral; French: Corail rouge; German: Rote Edelkoralle; Italian: Corallo rosso; Spanish: Coral rojo.

physical characteristics

Arborescent colonies with red calcium carbonate skeleton up to 19.5 in (50 cm) tall; feeding polyps with eight pinnate tentacles can be completely withdrawn into tissue; also possesses tiny non-feeding polyps (siphonozooids) that lack tentacles and contain the gonads; red calcareous spicules embedded in mesoglea.

distribution

Central and western Mediterranean Sea, with a few records from the eastern Mediterranean; Atlantic coast of southern Portugal and northern Africa.

habitat

Cave walls, vertical cliffs, and overhangs from a depth of 32–812 ft (10–250 m).

behavior

Nothing is known.

feeding ecology and diet

Captures small zooplankton from water column with tentacles. Also may directly absorb dissolved organic carbon from the water through epidermis.

reproductive biology

Gonochoristic; male colonies release sperm that swim and are carried by currents to female colonies; eggs are fertilized internally and brooded for up to 30 days. Nonfeeding larvae are released from June through October and swim for up to 15 days before settling. Limited capacity for asexual reproduction.

conservation status

Not listed by the IUCN or CITES. Population sizes are large but dominated by smaller, younger colonies, as larger colonies have been preferentially harvested. Commercial yields of precious coral declined from 100 tons (91,000 kg) in 1875 to 40 tons (36,000 kg) in 1989 and 27 tons (25,000 kg) in 1996. Underwent mass mortality in the northwestern Mediterranean in 1999 associated with abnormally high water temperatures.

significance to humans

The skeleton is highly valued for coral jewelry and has been harvested since Paleolithic times. It is commonly used by Navajo and other Native American craftspeople in the southwestern United States for inlays in fine handmade jewelry. The ancient Phoenicians, Egyptians and Romans used coral for trade. According to Greek legend, it confers such magical powers as overcoming evil, protecting crops, warding off epilepsy, defending ships against lightning, and eliminating hatred from the home. Powdered coral skeleton is sold as herbal or homeopathic medicine to be used as an antacid, astringent, emmenagogue, nervine tonic, laxative, diuretic, emetic, or antibilious agent. The traditional Indian Ayurvedic herbal medicine presents the following applications for C. rubrum skeleton: "Coughs, wasting, asthma, low fever, urinary diseases, carbuncles, scrofula, spermatorrhoea, gonorrhea and other genital inflammation with mucus discharge, nerve headaches, giddiness, vertigo, chronic bronchitis, pulmonary tuberculosis, vomiting, dyspepsia, bilious headache, weakness, and debility. It is added to tooth powders as an astringent. "

The term "coral" was originally applied to this species, and only subsequently to black corals, stony corals, and soft corals.

Red soft tree coral

Dendronephthya hemprichi

order

Alcyonacea

family

Nephtheidae

taxonomy

Spongodes hemprichi Klunzinger, 1877, Red Sea.

other common names

German: Hemprichs Schleierbäumchen; Italian: Alcionario rosa.

physical characteristics

Highly-branched, fleshy, arborescent (treelike) colony lacking an axial skeleton; large embedded sclerites are visible in branches and are conspicuous in polyps, producing a spiky appearance; polyps are not retractile and are mainly clustered in bundles at the end of branches; translucent, colors vary from red to pink, orange, or violet.

distribution

Red Sea.

habitat

Found only in strong currents, often on vertical surfaces. Dominant organism on artificial reefs and oil platforms in the Red Sea.

behavior

Nothing is known.

feeding ecology and diet

Suspension feeder almost exclusively on phytoplankton, a mode of nutrition considered rare among corals. Very small numbers of zooplankton also have been found in the gut. Lacks zooxanthellae.

reproductive biology

Gonochoristic, broadcast spawner releases gametes year round. Eggs may remain attached to the mouth by a thread of mucus for several minutes after spawning; when released, the eggs sink to the bottom. Larvae can metamorphose as soon as 27 hours or as long as 65 days after fertilization, and can live as long as 100 days. Dendronephthya hemprichi has a unique method of asexual reproduction: clusters of 4–12 polyps grow from the surface of the colony and autotomize (self-amputate) within two days; the detached polyp fragments have root-like processes that allow for rapid attachment to substrates. There may be hundreds of these fragments in a single colony, allowing for rapid clonal reproduction.

conservation status

Not listed by IUCN.

significance to humans

Dendronephthya corals are very popular attractions for divers and underwater photographers.

Black coral

Antipathella fiordensis

order

Antipatharia

family

Myriopathidae

taxonomy

Antipathes fiordensis Grange, 1990, Doubtful Sound, New Zealand.

other common names

None known.

physical characteristics

Densely branched tree-like colonies grow to over 16 ft (5 m) tall. Tiny polyps, arranged in rows, are white with six tentacles surrounding a mouth that is raised on an oral cone. Proteinaceous black skeleton is covered with spines.

distribution

Endemic to southwestern New Zealand.

habitat

Attached to the walls of fjords from 13 to over 325 ft (4 to over 100 m) in depth (but most abundant between 32–114 ft [10–35 m]). This habitat range is unusually shallow for black coral, which are typically found in deeper waters.

behavior

Produces sweeper tentacles, which are up to eight times longer, and more densely covered with nematocysts, than normal tentacles. Sweeper tentacles are used in aggressive interactions with other cnidarians in competition for space.

feeding ecology and diet

Diet consists of zooplankton, primarily copepods, which are captured by direct contact with the tentacles.

reproductive biology

Gonochoristic; broadcast spawns annually during the summer to produce free-swimming planula larvae.

conservation status

Endemic to the fjords of Fiordland in southwestern New Zealand. Population size has been estimated at more than seven million colonies. Black coral is a protected species in New Zealand, and all black corals are listed on CITES Appendix II.

significance to humans

The skeleton of black coral is used to make jewelry; however, no known fishery exists for A. fiordensis as of 2003.

American tube dwelling anemone

Ceriantheopsis americanus

order

Ceriantharia

family

Cerianthidae

taxonomy

Cerianthus americanus Agassiz in Verrill, 1864, Charleston, South Carolina, United States.

other common names

English: Burrowing mud anemone, North American tube anemone, tube sea anemone.

physical characteristics

Solitary, elongate, worm-like anemone up to 14 in (36cm) long and 0.79 in (2 cm) wide. Two rings of thin tentacles: up to 125 long ones around the outer edge of the oral disk, and an inner ring of short ones surrounding the mouth. Produces a soft, slippery, felt-like gray tube formed of ptychocysts, mucous, and debris. Colors range from brown or tan to maroon or purple.

distribution

Eastern coast of United States from Cape Cod south into the Gulf of Mexico; Caribbean; West Indies.

habitat

Intertidal zones up to 227 ft (70 m) deep; builds tube in vertical burrow as much as 18 in (45 cm) deep in muddy or sandy bottom; only the oral end emerges from the tube.

behavior

Will withdraw rapidly to bottom of tube when disturbed.

feeding ecology and diet

Spreads tentacles over the surface of the sand or mud to obtain food. Captures its prey with the longer outer tentacles and transfers it to the shorter tentacles surrounding the mouth.

reproductive biology

Hermaphroditic; fertilized eggs have been spawned in the laboratory, suggesting self-fertilization is possible.

conservation status

Not threatened.

significance to humans

Sold in the aquarium trade.

Elephant ear polyps

Amplexidiscus fenestrafer

order

Corallimorpharia

family

Actinodiscidae

taxonomy

Amplexidiscus fenestrafer Dunn and Hamner, 1980, Lizard Island, Great Barrier Reef, Australia.

other common names

English: Giant elephant ear mushroom anemone, disk anemone; French: Anémone disque; German: Grosses Elefantenohr; Italian: Anemone orecchio d'elefante.

physical characteristics

Short, column up to 2 in (5 cm) tall. Oral disc typically 8–10 in (20–25 cm), but as much as 18 in (45 cm), in diameter; mouth atop a raised cone. 15–20 tentacles around the margin, and many short, conical tentacles arranged in radial rows on the oral disc. A 0.4 in (10 mm) wide tentacle-free "window" rings the oral disc about 0.4 in (10 mm) from the margin. Color is a dull gray to greenish-brown.

distribution

Australia, Indonesia, Palau, and Guam.

habitat

In subtidal zones on coral reefs, usually in shallow, quiet water on the inshore side of the reef; attached to vertical walls or coral.

behavior

Nothing is known.

feeding ecology and diet

Captures prey by envelopment; the center of the oral disc is drawn down while the edges constrict to form a bowl that closes up like a drawstring within 3 sec, enclosing prey and up to 1 gal (4 l) of water. The prey, which may include zooplankton, shrimp and fishes, continues to swim or crawl within the enclosed space for 10–20 min after envelopment, after which it is swallowed. It has been suggested that A. fenestrafer mimics anemones that host anemonefish, thereby attracting anemonefish upon which it can feed. It also derives nutrition from symbiotic zooxanthellae harbored within cells lining the inside of the tentacles.

reproductive biology

Capable of asexual reproduction by longitudinal fission, pedal laceration, and budding from the column. Data on sexual reproduction are lacking, although individuals with functional male gonads have been identified.

conservation status

Not listed by the IUCN or CITES.

significance to humans

Sold in the aquarium trade.

Sea pansy

Renilla reniformis

order

Pennatulacea

family

Renillidae

taxonomy

Pennatula reniformis Pallas, 1766, "Mare Americum."

other common names

English: Atlantic coral.

physical characteristics

Colonial; a large primary polyp up to 3 in (7.5 cm) long and wide has a heart-shaped frond arising from a fleshy stalk. Smaller polyps are embedded in the upper surface of the frond: typical octocoral feeding polyps and tiny nonfeeding polyps lacking tentacles. Primary polyp appears purple because of colored sclerites in its tissue. The smaller embedded polyps are transparent.

distribution

Western Atlantic from North Carolina, United States, south to Tierra del Fuego, Argentina.

habitat

Stalk anchored in sand with frond lying flat on the surface, from low intertidal to shallow subtidal zones.

behavior

Produces bioluminescent bright green waves of light that run across the surface of the colony when disturbed at night. Small tentacle-less polyps act as water pumps, allowing colony to quickly deflate to half its normal size or expand.

feeding ecology and diet

Polyps secrete a sticky net of mucus that can trap small zooplankton.

reproductive biology

Nothing is known.

conservation status

Not listed by IUCN.

significance to humans

Bioluminescence is created by a protein called "Green Fluorescent Protein" (GFP). The GFP gene has been isolated and is sold commercially for use in molecular biological studies of gene expression in mammals. Scientists have isolated from the sea pansy unique diterpene lipids known as renillafoulins that prevent fouling organisms (e.g., barnacles) from settling on boats and other manufactured marine structures without killing them.

No common name

Acropora millepora

order

Scleractinia

family

Acroporidae

taxonomy

Heteropora millepora Ehrenberg, 1834, Indian Ocean.

other common names

None known.

physical characteristics

Colonial; thick finger-like interlocking branches with upright branchlets form squat colonies. Branch surfaces appear scaly. Tissue color ranges from green with orange tips to bright salmon pink or blue.

distribution

Tropical and subtropical Indo-Pacific waters, from Sri Lanka and Thailand east to the Marshall Islands and Tonga, including Australia.

habitat

Common on reef flats, lagoons, and upper reef slopes less than 10 ft (3 m) deep.

behavior

Mass spawning is timed to occur between 4 and 8 days following a full moon.

feeding ecology and diet

Feeds on minute zooplankton and derives nutrition from zooxanthellae harbored within cells lining the digestive cavity.

reproductive biology

Hermaphroditic polyps release bundles containing both sperm and eggs that float to the sea surface, where they break open and fertilization occurs. Planula larva may be competent to settle 4–5 days after fertilization. Asexual reproduction occurs by fragmentation of colony branches.

conservation status

All scleractinian corals are listed in CITES Appendix II.

significance to humans

Common reef-builder of Indo-Pacific coral reefs.

Elkhorn coral

Acropora palmata

order

Scleractinia

family

Acroporidae

taxonomy

Madrepora palmata Lamarck, 1816, "American Ocean."

other common names

Spanish: Cuerno de alce.

physical characteristics

Colonial; tree-like colonies up to 13 ft (4 m) across and 6.5 ft (2 m) tall, with thick branches broadly flattened near tips to resemble moose or elk antlers; tubular coral cups protrude from branch surface. Tissue tan or pale-brown, with tips of branches white.

distribution

Caribbean; Florida Keys, Bahamas, West Indies to Brazil.

habitat

Subtidal zones to 65 ft (20 m); densely aggregated thickets common on windward reef slopes exposed to heavy wave action.

behavior

Nothing is known.

feeding ecology and diet

Feed on minute zooplankton and derive nutrition from zooxanthellae harbored within cells lining the digestive cavity.

reproductive biology

Hermaphroditic polyps broadcast spawn once a year in August or September. Sperm and eggs are packaged together in bundles that float to the sea surface, where they break open and fertilization occurs. Planula larva are ready to settle 4–5 days after fertilization. Asexual reproduction occurs by fragmentation of colony branches. Damage to colonies caused by hurricanes is in part responsible for the large stands of A. palmata as broken branches reattach and produce new colonies.

conservation status

All scleractinian corals are listed in CITES Appendix II. Population declines across the Caribbean led to a designation as Candidate Species for listing as Threatened or Endangered under the U.S. Endangered Species Act in 1999. Population declines have been attributed to disease outbreaks (white band disease), compounded locally by hurricanes, increased predation, bleaching, and other factors. Poor water quality because of land-derived pollutants, sewage, and sediment may stress elkhorn coral and increase its susceptibility to disease.

significance to humans

Major structural component of Caribbean coral reefs. Provides essential habitat for fishes and other reef invertebrates. Cuts and scratches resulting from contact with elkhorn coral are reportedly slow to heal.

Deep water reef coral

Lophelia pertusa

order

Scleractinia

family

Caryophyllidae

taxonomy

Madrepora pertusa Linnaeus, 1758, type of locality not stated, but probably the fjords of Norway.

other common names

English: Spider hazards, spiders' nests (Nova Scotia); Norwegian: Glasskorall, øyekorall.

physical characteristics

Colonial; irregularly branched to form bushy or tree-like colonies up to 2 m tall; brittle tubular branches about 0.5 in (1–1.5 cm) thick; white or pink.

distribution

Most records are from the North Atlantic, but also known from the South Atlantic, northwestern Pacific; Indian Ocean; and waters south of New Zealand.

habitat

Cold water (39–53°F [4–12°C]) and deep sea, from 162 to >9750 ft (50 to >3000 m); hard substrates on slopes of continental margins and midoceanic islands. Colonies combine to build reefs and mounds as large as 650 ft (200 m) high, 0.6 mi (1 km) wide, and 3 mi (5 km) long. Studies have found L. pertusa associated with methane seeps, although this may simply be because these features represent topographic highs where ocean currents speed up, and not because L. pertusa is feeding on methane.

behavior

Nothing is known.

feeding ecology and diet

Feeds voraciously on zooplankton, including copepods.

reproductive biology

Details of sexual reproduction are unknown. Asexual reproduction of new colonies occurs when the fragile branches break and fragments continue to grow.

conservation status

Commercial deep-sea fish trawls are likely causing mechanical damage to Lophelia reefs. It is unknown what proportion of the coral fragments survive trawling damage. Lophelia reefs have received protected status in Norway. All scleractinian corals are listed in CITES Appendix II.

significance to humans

Provides a habitat for a diverse community of invertebrates and fishes.

No common name

Goniastrea aspera

order

Scleractinia

family

Faviidae

taxonomy

Goniastrea aspera Verrill, 1905, Hong Kong.

other common names

None known.

physical characteristics

Massive boulder-like or encrusting colonies; surface has a honeycomb-like appearance. Individual colonies may merge to form plateaus over 16 ft (5 m) across in intertidal zones. Color is usually pale brown; polyps have cream-colored centers.

distribution

Indo-Pacific; Red Sea, Indian Ocean, tropical and subtropical Pacific east to French Polynesia.

habitat

Intertidal to shallow subtidal zones; can withstand pounding surf and several hours of exposure to tropical sun and air.

behavior

Nothing is known.

feeding ecology and diet

Derive nutrition from symbiotic zooxanthellae harbored within cells lining the digestive cavity, and may feed on minute zooplankton.

reproductive biology

Hermaphroditic broadcast spawner; may release buoyant sperm and egg bundles, or eggs may be released moments before sperm. In the latter case, some eggs may be retained, with fertilization and development taking place within the polyp. Spawned larvae may settle within five days, but brooded larvae may remain within polyp for 18 days. Asexual reproduction by colony fission possible, but is not common.

conservation status

All scleractinian corals are listed in CITES Appendix II. Studies have shown that low concentrations of copper or nickel negatively affect reproductive success. A similar effect is seen with relatively small increases in nutrients, as would occur from eutrophication (algae overgrowth associated with excessive amounts of nutrients in the water) resulting from human activity.

significance to humans

None known.

Mushroom coral

Fungia scutaria

order

Scleractinia

family

Fungiidae

taxonomy

Fungia scutaria Lamarck, 1801, no locality given.

other common names

English: Plate coral; German: Pilzkoralle, Rasiermesserkoralle; Hawaiian: ko'a-kohe

physical characteristics

Solitary and free-living (unattached) as an adult; oval to elongate skeleton from 1–7 in (2.5–18 cm) long resembles the underside of a toadstool mushroom; numerous small tentacles

arise from lobes formed by underlying skeleton. Usually brown with irregular pink or violet patches; tentacular lobes often bright green.

distribution

Red Sea, Indian Ocean south to Madagascar, west into Pacific Ocean to Society Islands, north to Hawaiian and Line Islands.

habitat

On upper reef slopes exposed to strong wave action or around coral knolls at depths from 1.5–16 ft (0.5–5 m).

behavior

In the Red Sea, spawning is synchronized to occur in the late afternoon 1–4 days after a full moon. Free-living, unattached adults that are overturned by wave action can right themselves by taking in water through the mouth to expand one-half of the body. This process may take several hours.

feeding ecology and diet

May feed on particulate organic material from water column. Derives nutrition from symbiotic zooxanthellae harbored within cells lining the digestive cavity.

reproductive biology

Gonochoristic, broadcast spawners; males are smaller than females. Larvae acquire zooxanthellae in the water column. Larvae attach to the bottom and grow a short, calcareous stalk that eventually breaks, releasing the wide upper disk that becomes the free-living adult. The attached stalk may continue to grow and break off new polyps. Asexual reproduction by budding from adult tissue is also seen.

conservation status

All scleractinian corals are listed in CITES Appendix II.

significance to humans

Skeleton was used by early Hawaiians as an abrasive for polishing wooden canoes and for removing bristles from pig skins before cooking.

Cauliflower coral

Pocillopora damicornis

order

Scleractinia

family

Pocilloporidae

taxonomy

Millepora damicornis Linnaeus, 1758, "Oceanus Asiatico."

other common names

English: Bird's nest coral, lace coral; German: Buschkoralle.

physical characteristics

Colonial; the colony is a compact clump, up to several meters across, formed of branches; the surface is dotted with verrucae (wartlike bumps) that intergrade with the branches. Growth form varies with environmental conditions and geographic location. Tissue color is pale brown, greenish, or pink.

distribution

Throughout the Indo-Pacific, western and eastern Australia, north to Japan and Hawaii, and east to Central America, Mexico and Ecuador.

habitat

Common in all shallow-water habitats, from wharf piles and mangrove swamps to exposed reef fronts; rarely grows deeper than 30 ft (9 m).

behavior

Polyp tentacles are usually extended only at night.

feeding ecology and diet

Feeds on minute zooplankton and derives nutrition from zooxanthellae harbored within cells lining the digestive cavity.

reproductive biology

Polyps are hermaphroditic. Unlike most corals, eggs are fertilized internally and brooded (although in the eastern Pacific, P. damicornis is a broadcast spawner). Asexual production of larvae also has been reported. Larvae released from polyps can delay settlement for 100 days or longer, and therefore have the potential to travel great distances. Larvae acquire zooxanthellae from parent.

conservation status

All scleractinian corals are listed in CITES Appendix II.

significance to humans

Pocilloporids are among the most successful colonizers of coral reefs following disturbance, and are an important frame-building species.

Rubber coral

Palythoa caesia

order

Zoanthidea

family

Sphenopidae

taxonomy

Palythoa caesia Dana, 1846, "Feejee Islands."

other common names

English: Palythoa sea mat

physical characteristics

Mat-like colonies appear rubbery in texture; typically form ovoid blobs 2–4 in (5–10 cm) in diameter. Polyps are completely embedded in thick coenenchyme encrusted with sediment; short, simple tentacles with knobbed tips. Color ranges from dark brown to tan.

distribution

Indo-Pacific.

habitat

Intertidal or subtidal zones on coral reefs and reef crests. In areas of high abundance, may form mats covering virtually all of the available substrate for tens to hundreds of square meters.

behavior

Nothing is known.

feeding ecology and diet

Contains symbiotic zooxanthellae in its tissues. In laboratory studies, P. caesia feeds on zooplankton, algae, and bacteria.

reproductive biology

Broadcast spawner. Eggs and larvae lack zooxanthellae, so symbionts must be acquired after settlement.

conservation status

Not listed by the IUCN or CITES.

significance to humans

Palytoxins, which are found in the mucus and gonads of Palythoa caesia, are among the most potent toxins known in nature and can be painful and dangerous to humans if absorbed through open wounds. Ancient Hawaiians coated their spear tips with these toxins.

Resources

Books

Davies, P. S. "Anthozoan Endosymbiosis." In Proceedings of the Sixth International Conference on Coelenterate Biology, edited by J. C. den Hartog. Leiden: National Natuurhistorisch Museum, 1997.

Dayton, P. K., K. W. England, and E. A. Robson. "An Unusual Sea Anemone, Dactylanthus antarcticus (Clubb, 1908) (Order Ptychodactiaria), on Gorgonians in Chilean Fjords." In Proceedings of the Sixth International Conference on Coelenterate Biology, edited by J. C. den Hartog. Leiden: National Natuurhistorisch Museum, 1997.

Fabricius, Katharina, and Philip Alderslade. Soft Corals and Sea Fans. Townsville: Australian Institute of Marine Science, 2001.

Friese, U. Erich. Sea Anemones…As a Hobby. Neptune City, NJ: T. F. H. Publications, Inc., 1993.

Martin, Vicki J. "Cnidarians, the Jellyfish and Hydras." In Embryology: Constructing the Organism, edited by Scott F. Gilbert and Anne M. Raunio. Sunderland, MA: Sinauer Associates, Inc., 1997.

Shick, J. Malcolm. A Functional Biology of Sea Anemones. New York: Chapman & Hall, 1991.

Veron, John E. N. Corals of the World. Townsville: Australian Institute of Marine Science, 2000.

Wallace, Carden C. Staghorn Corals of the World. Collingwood: CSIRO, 1999.

Watling, Les, and Michael Risk, eds. Biology of Cold Water Corals. Vol. 471, Hydrobiologia. Dordrecht: Kluwer Academic Publishers, 2002.

Periodicals

Allemand, Denis. "The Biology and Skeletogenesis of the Mediterranean Red Coral." Precious Corals and Octocoral Research 2 (1993): 19–39.

Berntson, Ewann A., Scott C. France, and Lauren S. Mullineaux. "Phylogenetic Relationships within the Class Anthozoa (Phylum Cnidaria) Based on Nuclear 18s RDNA Sequences." Molecular Phylogenetics and Evolution 13, no. 2 (1999): 417–433.

Bruckner, Andrew W. "Tracking the Trade in Ornamental Coral Reef Organisms: The Importance of CITES and Its Limitations." Aquarium Sciences and Conservation 3 (2001): 79–94.

Cappola, Valerie A., and Daphne G. Fautin. "All Three Species of Ptychodactiaria Belong to Order Actiniaria (Cnidaria: Anthozoa)." Journal of the Marine Biological Association of the United Kingdom 80 (2000): 995–1003.

Druffel, Ellen R. M., Sheila Griffin, Amy Witter, Erle Nelson, John Southon, Michaele Kashgarian, and John Vogel. "Gerardia: Bristlecone Pine of the Deep-Sea?" Geochimica et Cosmochimicha Acta 59, no. 23 (1995): 5031–5036.

Fabricius, Katharina E., Yehuda Benayahu, and Amatzia Genin. "Herbivory in Asymbiotic Soft Corals." Science 268 (1995): 90–92.

Fautin, Daphne G. "Reproduction of Cnidaria." Canadian Journal of Zoology 80 (2002): 1735–1754.

Frank, Uri, and Ofer Mokady. "Coral Biodiversity and Evolution: Recent Molecular Contributions." Canadian Journal of Zoology 80 (2002): 1723–1734.

Garrabou, J., T. Perez, S. Sartoretto, and J. G. Harmelin. "Mass Mortality Event in Red Coral Corallium rubrum Populations in the Provence Region (France, NW Mediterranean)." Marine Ecology Progress Series 217 (2001): 263–272.

Grigg, Richard W. "Precious Coral Fisheries of Hawaii and the U.S. Pacific Islands." Marine Fisheries Reviews 55, no. 2 (1993): 50–60.

Hall-Spencer, Jason, Valerie Allain, and Jan H. Fosså. "Trawling Damage to Northeast Atlantic Ancient Coral Reefs." Proceedings of the Royal Society of London, Series B: Biological Sciences 269, no. 1490 (2002): 507–511.

Hand, Cadet, and Kevin R. Uhlinger. "The Unique, Widely Distributed, Estuarine Sea Anemone, Nematostella vectensis Stephenson: A Review, New Facts, and Questions." Estuaries 17, no. 2 (1994): 501–508.

Hatta, Masayuki, Hironobu Fukami, Wenqia Wang, Makoto Omori, Kazuyuki Shimoike, Takeshi Hayashibara, Yasuo Ina, and Tsutomu Sugiyama. "Reproductive and Genetic Evidence for a Reticulate Evolutionary History of Mass-Spawning Corals." Molecular Biology and Evolution 16, no. 11 (1999): 1607–1613.

Hodgson, G. "A Global Assessment of Human Effects on Coral Reefs." Marine Pollution Bulletin 38, no. 5 (1999): 345–355.

Parker, N.R., P.V. Mladenov, and K.R. Grange. "Reproductive Biology of the Antipatharian Black Coral Antipathes Fiordensis in Doubtful Sound, Fiordland, New Zealand." Marine Biology 130 (1997): 11–22.

Pearson, C.V.M., A. D. Rogers, and M. Sheader. "The Genetic Structure of the Rare Lagoonal Sea Anemone, Nematostella vectensis Stephenson (Cnidaria; Anthozoa) in the United Kingdom Based on RAPD Analysis." Molecular Ecology 11 (2002): 2285–2293.

Rogers, Alex D. "The Biology of Lophelia pertusa (Linnaeus 1758) and Other Deep-Water Reef-Forming Corals and Impacts from Human Activities." International Review of Hydrobiology 84, no. 4 (1999): 315–406.

Ryland, John S. "Reproduction in Zoanthidea (Anthozoa: Hexacorallia)." Invertebrate Reproduction and Development 31, no. 1–3 (1997): 177–188.

Santangelo, Giovanni, and Marco Abbiati. "Red Coral: Conservation and Management of an Over-Exploited Mediterranean Species." Aquatic Conservation: Marine and Freshwater Ecosystems 11 (2001): 253–259.

Slattery, Marc, James B. McClintock, and Sam S. Bowser. "Deposit Feeding: A Novel Mode of Nutrition in the Antarctic Colonial Soft Coral Gersemia antarctica." Marine Ecology Progress Series 149 (1997): 299–304.