Cnidaria, is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are a decentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable flagella used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians are also some of the only animals that can reproduce both sexually and asexually.
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral end is attached to the substrate by means of a disc-like holdfast called a pedal disc, while in colonies of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the mouth, and is surrounded by a circlet of tentacles.
Anthozoa is a class of marine invertebrates which includes the sea anemones, stony corals and soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plankton. The basic unit of the adult is the polyp; this consists of a cylindrical column topped by a disc with a central mouth surrounded by tentacles. Sea anemones are mostly solitary, but the majority of corals are colonial, being formed by the budding of new polyps from an original, founding individual. Colonies are strengthened by calcium carbonate and other materials and take various massive, plate-like, bushy or leafy forms.
Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mouth is fringed with tentacles. Although some species are solitary, most are colonial. The founding polyp settles and starts to secrete calcium carbonate to protect its soft body. Solitary corals can be as much as 25 cm (10 in) across but in colonial species the polyps are usually only a few millimetres in diameter. These polyps reproduce asexually by budding, but remain attached to each other, forming a multi-polyp colony of clones with a common skeleton, which may be up to several metres in diameter or height according to species.
The aggregating anemone, or clonal anemone, is the most abundant species of sea anemone found on rocky, tide swept shores along the Pacific coast of North America. This cnidarian hosts endosymbiotic algae called zooxanthellae that contribute substantially to primary productivity in the intertidal zone. The aggregating anemone has become a model organism for the study of temperate cnidarian-algal symbioses.
Tube-dwelling anemones or ceriantharians look very similar to sea anemones but belong to an entirely different class of anthozoans. They are solitary, living buried in soft sediments. Tube anemones live inside and can withdraw into tubes, which are composed of a fibrous material made from secreted mucus and threads of nematocyst-like organelles known as ptychocysts. Within the tubes of these ceriantharians, more than one polyp is present, which is an exceptional trait because species that create tube systems usually contain only one polyp per tube. Ceriantharians were formerly classified in the taxon Ceriantipatharia along with the black corals but have since been moved to their own class, Ceriantharia.
Zoanthids are an order of cnidarians commonly found in coral reefs, the deep sea and many other marine environments around the world. These animals come in a variety of different colonizing formations and in numerous different colors. They can be found as individual polyps, attached by a fleshy stolon or a mat that can be created from small pieces of sediment, sand and rock. The term "zoanthid" refers to all animals within this order Zoantharia, and should not be confused with "Zoanthus", which is one genus within Zoantharia.
Hexacorallia is a class of Anthozoa comprising approximately 4,300 species of aquatic organisms formed of polyps, generally with 6-fold symmetry. It includes all of the stony corals, most of which are colonial and reef-forming, as well as all sea anemones, and zoanthids, arranged within five extant orders. The hexacorallia are distinguished from another class of Anthozoa, Octocorallia, in having six or fewer axes of symmetry in their body structure; the tentacles are simple and unbranched and normally number more than eight. These organisms are formed of individual soft polyps which in some species live in colonies and can secrete a calcite skeleton. As with all Cnidarians, these organisms have a complex life cycle including a motile planktonic phase and a later characteristic sessile phase. Hexacorallia also include the significant extinct order of rugose corals.
Aiptasia is a genus of a symbiotic cnidarian belonging to the class Anthozoa. Aiptasia is a widely distributed genus of temperate and tropical sea anemones of benthic lifestyle typically found living on mangrove roots and hard substrates. These anemones, as well as many other cnidarian species, often contain symbiotic dinoflagellate unicellular algae of the genus Symbiodinium living inside nutritive cells. The symbionts provide food mainly in the form of lipids and sugars produced from photosynthesis to the host while the hosts provides inorganic nutrients and a constant and protective environment to the algae. Species of Aiptasia are relatively weedy anemones able to withstand a relatively wide range of salinities and other water quality conditions. In the case of A. pallida and A. pulchella, their hardiness coupled with their ability to reproduce very quickly and out-compete other species in culture gives these anemones the status of pest from the perspective of coral reef aquarium hobbyists. These very characteristics make them easy to grow in the laboratory and thus they are extensively used as model organisms for scientific study. In this respect, Aiptasia have contributed a significant amount of knowledge regarding cnidarian biology, especially human understanding of cnidarian-algal symbioses, a biological phenomenon crucial to the survival of corals and coral reef ecosystems. The dependence of coral reefs on the health of the symbiosis is dramatically illustrated by the devastating effects experienced by corals due to the loss of algal symbionts in response to environmental stress, a phenomenon known as coral bleaching.
Corallimorpharia is an order of marine cnidarians closely related to stony or reef building corals (Scleractinia). They occur in both temperate and tropical climates, although they are mostly tropical. Temperate forms tend to be very robust, with wide and long columns, whereas tropical forms tend to have very short columns with a wide oral disc and very short tentacles. The tentacles are usually arranged in rows radiating from the mouth. Many species occur together in large groups, although there are recorded instances of individuals. In many respects, they resemble the stony corals, except for the absence of a stony skeleton. Morphological and molecular evidence suggests that they are very closely related to stony corals.
Sea anemones are a group of predatory marine invertebrates constituting the order Actiniaria. Because of their colourful appearance, they are named after the Anemone, a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Hexacorallia. As cnidarians, sea anemones are related to corals, jellyfish, tube-dwelling anemones, and Hydra. Unlike jellyfish, sea anemones do not have a medusa stage in their life cycle.
Zoanthus sociatus, commonly known as the green sea mat or button polyp, is a zoanthid usually found in shallow reef zones of tropical regions from Caribbean to southeastern Brazil. Z. sociatus is currently being studied for its use against human lymphatic parasites.
Corynactis annulata, or the strawberry anemone, is a bright pink colonial anthozoan similar in body form to sea anemones and scleractinian stony corals. This species is a solitary animal of the order Corallimorpharia.
Corynactis is a genus of colonial anthozoans similar in appearance to sea anemones and in body format to scleractinian stony corals. These animals are cnidarians in the family Corallimorphidae. Large unidentified polyps of this genus feed on the crown-of-thorns seastar Acanthaster planci and may help control the crown-of-thorns population.
Anthothoe albocincta, or white-striped anemone, is a species of sea anemone in the family Sagartiidae. It is native to the coasts of Australia and New Zealand.
Pavona cactus, the cactus coral, potato chip coral or leaf coral, is a species of colonial stony coral in the family Agariciidae. This coral is found in shallow waters on reefs and in lagoons in tropical parts of the Indo-Pacific region.
Paracorynactis is a genus of corallimorphs from the western Indo-West Pacific. They are specialized predators of echinoderms, and are notable for preying on the destructive crown-of-thorns starfish among others. The genus is monotypic with the single species, Paracorynactis hoplites.
Cycloseris curvata is a species of disc coral in the family Fungiidae. Cyclosteris curvata is a mostly solitary free living scleractinian disc coral found in the indo-pacific region. They grow on soft substrates and are known to tolerate turbid waters. Like other anthozoan corals they lack a medusa stage characteristic of other cnidarians. They have been observed as both green and brown in color in the field.
Ricordea yuma is a species of coral in the family Ricordeidae, order Corallimorpharia; This order of corals do not produce the distinctive calcification of the closely related Scleractinian, or reef building corals. Ricordea yuma are found on the sea floor in relatively shallow, tropical or subtropical ocean environments. Distinctive features include a large mouth disk that takes up most of the organism, and brightly colored tentacles. Ricordea yuma can reproduce both sexually, and asexually by budding a new coral with replicated elements from the mother coral. This may be one mechanism of how they are able to spread and overtake areas rapidly; They have been observed being competitively successful at monopolizing areas by excluding reef-building coral species, after a disturbance in the substrate.
Corynactis viridis, the jewel anemone, is a brightly coloured anthozoan similar in body form to a sea anemone or a scleractinian coral polyp, but in the order Corallimorpharia. It is found in the northeastern Atlantic Ocean and the Mediterranean Sea and was first described by the Irish naturalist George Allman in 1846.
