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28-417: See text Alcyonacea are an order of sessile colonial cnidarians that are found throughout the oceans of the world, especially in the deep sea, polar waters, tropics and subtropics . Whilst not in a strict taxonomic sense, Alcyonacea are commonly known as soft corals . The term "soft coral" generally applies to organisms in the two orders Pennatulacea and Alcyonacea with their polyps embedded within

56-403: A tentacle is a flexible, mobile, and elongated organ present in some species of animals , most of them invertebrates . In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work mainly like muscular hydrostats . Most forms of tentacles are used for grasping and feeding. Many are sensory organs , variously receptive to touch , vision , or to

84-649: A fleshy mass of coenenchymal tissue. Consequently, the term "gorgonian coral" is commonly handed to multiple species in the order Alcyonacea that produce a mineralized skeletal axis (or axial-like layer) composed of calcite and the proteinaceous material gorgonin only and corresponds to only one of several families within the formally accepted taxon Gorgoniidae ( Scleractinia ). These can be found in order Malacalcyonacea (taxonomic synonyms of include (unnacepted): Alcyoniina , Holaxonia , Protoalcyonaria , Scleraxonia , and Stolonifera . Common names for subsets of this order are sea fans and sea whips ; others are similar to

112-420: A major energy source. However, most readily eat any free-floating food, such as zooplankton, out of the water column. They are integral members of the reef ecosystem and provide habitat for fish, snails, algae, and a diversity of other marine species. Despite being dominated by "soft corals", the order Alcyonacea now contains all species known as "gorgonian corals", that produce a hard skeleton made from gorgonin,

140-769: A particular species group closely to one another for beneficial purposes, as can be seen in coral reefs and cochineal populations. This allows for faster reproduction and better protection from predators. The circalittoral zone of coastal environments and biomes are dominated by sessile organisms such as oysters . Carbonate platforms grow due to the buildup of skeletal remains of sessile organisms, usually microorganisms , which induce carbonate precipitation through their metabolism. In anatomy and botany, sessility refers to an organism or biological structure that has no peduncle or stalk. A sessile structure has no stalk. See : peduncle (anatomy) , peduncle (botany) and sessility (botany) . Tentacle In zoology ,

168-665: A protein unique to the group that makes their skeletons quite different from "true" corals ( Scleractinia ). These "gorgonion corals" can be found in suborders Holaxonia, Scleraxonia, and Stolonifera . Many soft corals are easily collected in the wild for the reef aquarium hobby, as small cuttings are less prone to infection or damage during shipping than stony corals. Nevertheless, home-grown specimens tend to be more adaptable to aquarium life and help conserve wild reefs. Soft corals grow quickly in captivity and are easily divided into new individuals, and so those grown by aquaculture are often hardier and less expensive than imported corals from

196-400: A solid object, such as a rock, a dead tree trunk, or a human-made object such as a buoy or ship's hull. Sessile animals typically have a motile phase in their development. Sponges have a motile larval stage and become sessile at maturity. Conversely, many jellyfish develop as sessile polyps early in their life cycle. In the case of the cochineal , it is in the nymph stage (also called

224-502: A spiky, grainy texture that deters predators. In the past, soft corals were thought to be unable to lay new foundations for future corals, but recent findings suggest that colonies of the leather-coral genus Sinularia are able to cement sclerites and consolidate them at their base into alcyonarian spiculite, thus making them reef builders. Unlike stony corals , most soft corals thrive in nutrient-rich waters with less intense light. Almost all use symbiotic photosynthetic zooxanthella as

252-510: Is a layer of helical muscle that helps each tentacle to twist or turn in any direction where the prey is sensed. The modern convention, however, is to speak of appendages as "tentacles" when they have relatively thin " peduncles " or "stalks" with "clubs" at their tips. In contrast the convention refers to the relatively shorter appendages as "arms". By this definition the eight appendages of octopuses, though quite long, count as arms. While arms are distinct from tentacles (a definition specific to

280-499: Is limited to two species in the single genus Muricella . Gorgonians produce unusual organic compounds in their tissues, particularly diterpenes , and some of these are important candidates for new drugs. These compounds may be part of the chemical defenses produced by gorgonians to render their tissue distasteful to potential predators. Bottlenose dolphins in the Red Sea have been observed swimming against these tissues, in what

308-459: Is thought to be an attempt to take advantage of the antimicrobial qualities of diterpenes . Despite these chemical defenses, the tissues of gorgonians are prey for flamingo tongue snails of the genus Cyphoma , nudibranchs , the fireworm Hermodice spp., and their polyps are food for butterflyfishes . Amongst the nudibranchs which feed on soft corals and sea fans are the Tritoniidae and

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336-453: Is why the most widely accepted theory explaining the evolution of a larval stage is the need for long-distance dispersal ability. Biologist Wayne Sousa 's 1979 study in intertidal disturbance added support for the theory of nonequilibrium community structure, "suggesting that open space is necessary for the maintenance of diversity in most communities of sessile organisms". Clumping is a behavior in sessile organisms in which individuals of

364-516: The pulmonate land snails , which usually have two sets of tentacles on the head: when extended the upper pair have eyes at their tips; the lower pair are chemoreceptors . Both pairs are fully retractable muscular hydrostats , but they are not used for manipulation or prey capture. Molluscs have one pair of tentacles close to their mouths that hold close to their captured prey before they can consume it. Some marine snails such as abalone and top snails, Trochidae , have numerous small tentacles around

392-482: The smell or taste of particular foods or threats. Examples of such tentacles are the eyestalks of various kinds of snails . Some kinds of tentacles have both sensory and manipulatory functions. A tentacle is similar to a cirrus , but a cirrus is an organ that usually lacks the tentacle's strength, size, flexibility, or sensitivity. A nautilus has cirri, but a squid has tentacles. Many molluscs have tentacles of one form or another. The most familiar are those of

420-585: The adult cestode to attach to the intestine of the shark or ray that they parasitize. The same tentacles are also present in the larvae. The legless amphibians called caecilians have two short tentacles, one on each side of the head, between their eyes and nostrils. The current opinion is that these tentacles supplement the normal sense of smell, possibly for navigation and to locate prey underground. The star-nosed mole , Condylura cristata , of North America , has 22 short but conspicuous tentacles around its nose. They are mobile and extremely sensitive, helping

448-489: The animal to find its way about the burrow and detect prey. They are about 1–4 mm long and hold about 25,000 touch receptors called Eimer's organs , perhaps giving this mole the most delicate sense of touch among mammals. The word tentillum ( pl. : tentilla ) literally means "little tentacle". However, irrespective of size, it usually refers to a side branch of a larger tentacle. In some cases, such tentilla are specialised for particular functions; for example, in

476-584: The body is below with the tentacles pointed upwards. The tentacles of the lion's mane jellyfish may be up to 37 m (121 ft) long. They are hollow and are arranged in 8 groups of between 70 and 150. The longer tentacles are equipped with cnidocytes whose venom paralyses and kills prey. The smaller tentacles guide food into the mouth. Many species of the jellyfish-like ctenophores have two tentacles, while some have none. Their tentacles have adhesive structures called colloblasts or lasso cells . The colloblasts burst open when prey comes in contact with

504-399: The colossal squid wield two long rows of swiveling, tri-pointed hooks. Cnidarians , such as jellyfish , sea anemones , Hydra and coral have numerous hair-like tentacles. Cnidarians have huge numbers of cnidocytes on their tentacles. In medusoid form , the body floats on water so that the tentacles hang down in a ring around the mouth. In polyp form, such as sea anemone and coral,

532-521: The crawler stage) that the cochineal disperses. The juveniles move to a feeding spot and produce long wax filaments. Later they move to the edge of the cactus pad where the wind catches the wax filaments and carries the tiny larval cochineals to a new host. Many sessile animals, including sponges, corals and hydra , are capable of asexual reproduction in situ by the process of budding . Sessile organisms such as barnacles and tunicates need some mechanism to move their young into new territory. This

560-492: The edge of the mantle . These are known as pallial tentacles . Among cephalopods , squid have spectacular tentacles. They take the form of highly mobile muscular hydrostats with various appendages such as suction disks and sometimes thorny hooks. Up to the early twentieth century "tentacles" were interchangeably called "arms". These tentacles are made of stalks of axial nerve cords that are covered by circular transverse muscle tissue that contract in response to stimuli. There

588-421: The genus Phyllodesmium which specialises in eating Xenia species. The World Register of Marine Species lists these suborders and families : Sessility (zoology) Sessile animals can move via external forces (such as water currents), but are usually permanently attached to something. Organisms such as corals lay down their own substrate from which they grow. Other animals organisms grow from

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616-418: The gorgonin and calcite within several long-lived species of gorgonians can be useful in paleoclimatology and paleoceanography , as their skeletal growth rate and composition are highly correlated with seasonal and climatic variation. Soft corals contain minute, spiny skeletal elements called sclerites , useful in species identification. Sclerites give these corals some degree of support and give their flesh

644-406: The limb featuring peduncles), arms do fall within the general definition of "tentacle" as "a flexible, mobile, and elongated organ" and "tentacle" could be used as an umbrella term . The tentacles of the giant squid and colossal squid have powerful suckers and pointed teeth at the ends. The teeth of the giant squid resemble bottle caps and function like tiny hole saws , while the tentacles of

672-590: The oceans of the world, but they are particularly abundant in the shallow waters of the Western Atlantic, including Florida , Bermuda , and the West Indies. The structure of a gorgonian colony varies. In the suborder Holaxonia, skeletons are formed from a flexible, horny substance called gorgonin . The suborder Scleraxonia species are supported by a skeleton of tightly grouped calcareous spicules. Also, some species encrust like coral. Measurements of

700-476: The sea pens of related order Pennatulacea . Individual tiny polyps form colonies that are normally erect, flattened, branching, and reminiscent of a fan . Others may be whiplike, bushy, or even encrusting. A colony can be several feet high and across, but only a few inches thick. They may be brightly coloured, often purple, red, or yellow. Photosynthetic gorgonians can be successfully kept in captive aquaria . About 500 different species of gorgonians are found in

728-489: The taller, thinner, and stiffer gorgonians can be found in deeper, calmer waters. Other fauna, such as hydrozoa , bryozoa , and brittle stars , are known to dwell within the branches of gorgonian colonies. The pygmy seahorse not only makes certain species of gorgonians its home, but also closely resembles its host, thus is well camouflaged. Two species of pygmy seahorse, Hippocampus bargibanti and Hippocampus denise , are obligate residents on gorgonians. H. bargibanti

756-451: The tentacle, releasing sticky threads that secure the food. Bryozoa (moss animals) are tiny creatures with tentacles around their mouths. The tentacles are almost cylindrical and have bands of cilia which create a water current towards the mouth. The animal extracts edible material from the flow of water. Trypanorhynch cestodes are parasitic in fish. Their scolex shows four tentacles which are covered by spines. These tentacles help

784-824: The wild. Each gorgonian polyp has eight tentacles , which catch plankton and particulate matter for consumption. This process, called filter feeding , is facilitated when the "fan" is oriented across the prevailing current to maximise water flow to the gorgonian, hence food supply. Some gorgonians contain algae, or zooxanthellae . This symbiotic relationship assists in giving the gorgonian nutrition by photosynthesis . Gorgonians possessing zooxanthellae are usually characterized by brownish polyps. Gorgonians are found primarily in shallow waters, though some have been found at depths of several thousand feet. The size, shape, and appearance of gorgonians can be correlated with their location. The more fan-shaped and flexible gorgonians tend to populate shallower areas with strong currents, while

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