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Planula
A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores, which are not related to cnidarians at all. Some groups of Nemerteans also produce larvae that are very similar to the planula, which are called planuliform larva. In a few cnidarian clades, like Aplanulata and the parasitic Myxozoa, the planula larval stage has been lost. Development The planula forms either from the fertilized egg of a medusa, as is the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans. Depending on the species, the planula either metamorphoses directly into a free-swimming, miniature version of the mobile adult form, or navigates through the water until it reaches a hard substrate (many may prefer specific substrates) where it anchors and grows into a polyp. The miniature-adult types include many open-ocean scyphozoans. The attaching types include all anthozoans w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cnidarian Biology
Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in freshwater and marine environments (predominantly the latter), including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are an uncentralized 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 few animals that can reproduce both sexually and asexually. Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes, which are specialized stinging cells used to capt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cnidaria
Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are an uncentralized 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 (biology), cell thick. Cnidarians are also some of the few animals that can reproduce both sexually and asexually. Cnidarians mostly have two basic body forms: swimming medusa (biology), medusae and sessility (motility), sessile polyp (zoology), polyps, both of which are radially symmetrical with mou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Medusozoa
Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. It includes the classes Hydrozoa, Scyphozoa, Staurozoa and Box jellyfish, Cubozoa, and possibly the parasitic Polypodium (animal), Polypodiozoa. Medusozoans are distinguished by having a medusa stage in their often complex life cycle, a medusa typically being an umbrella-shaped body with stinging tentacles around the edge. With the exception of some Hydrozoa (and Polypodiozoa), all are called jellyfish in their free-swimming Jellyfish#Life history and behavior, medusa phase. Evolution The phylum Cnidaria is widely accepted as being Monophyly, monophyletic and consisting of two clades, Anthozoa and Medusozoa. Anthozoa includes the Class (biology), classes Hexacorallia, the hard corals, and Octocorallia, the soft corals, as well as Tube-dwelling anemone, Ceriantharia, the tube-dwelling anemones. There is strong support for this group having been the first to branch off from the ancestral line. Meduso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrozoa
Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colony (biology), colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genus, genera within this class live in freshwater ecosystem, freshwater habitats. Hydrozoans are related to jellyfish and corals, which also belong to the phylum (biology), phylum Cnidaria. Some examples of hydrozoans are the freshwater jelly (''Craspedacusta sowerbyi''), freshwater polyps (''Hydra (genus), Hydra''), ''Obelia'', Portuguese man o' war (''Physalia physalis''), chondrophores (Porpitidae), and pink-hearted hydroids (''Tubularia''). Anatomy Most hydrozoan species include both a polyp (zoology), polypoid and a medusa (biology), medusoid stage in their Biological ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aboral
Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes, axes. The meaning of terms that are used can change depending on whether a vertebrate is a biped or a quadruped, due to the difference in the neuraxis, or if an invertebrate is a non-bilaterian. A non-bilaterian has no anterior or posterior surface for example but can still have a descriptor used such as proximal or distal in relation to a body part that is nearest to, or furthest from its middle. International organisations have determined vocabularies that are often used as standards for subdisciplines of anatomy. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anthozoa
Anthozoa is one of the three subphyla of Cnidaria, along with Medusozoa and Endocnidozoa. It includes Sessility (motility), sessile marine invertebrates and invertebrates of brackish water, such as sea anemones, Scleractinia, stony corals, soft corals and sea pens. Almost all adult anthozoans are attached to the seabed, while their larvae can disperse as plankton. The basic unit of the adult is the polyp (zoology), polyp, an individual animal consisting 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 colony (biology), colonial, being formed by the budding of new polyps from an original, founding individual. Colonies of stony corals are strengthened by mainly aragonite and other materials, and can take various massive, plate-like, bushy or leafy forms. Members of Anthozoa possess cnidocytes, a feature shared among other cnidarians such as the jellyfish, box jellyfish, box jellies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyp (zoology)
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa (biology), medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end is attached to the substrate (biology), substrate by means of a disc-like holdfast (biology), holdfast called a pedal disc, while in colony (biology), 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. Classes In the class Anthozoa, comprising the sea anemones and corals, the individual is always a polyp; in the class Hydrozoa, however, the individual may be either a polyp or a medusa (biology), medusa, with most species undergoing a biological life cycle, life cycle with both a polyp stage and a medusa stage. In the class Scyphozoa, the medusa stage is dominant, and the polyp stage may or may not be present, depen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cilium
The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body. Eukaryotic flagella found on sperm cells and many protozoans have a similar structure to motile cilia that enables swimming through liquids; they are longer than cilia and have a different undulating motion. There are two major classes of cilia: ''motile'' and ''non-motile'' cilia, each with two subtypes, giving four types in all. A cell will typically have one primary cilium or many motile cilia. The structure of the cilium core, called the axoneme, determines the cilium class. Most motile cilia have a central pair of single microtubules surrounded by nine pairs of double microtubules called a 9+2 axoneme. Most non-motile cilia have a 9+0 axoneme that lacks the centr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scyphozoa
The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek word '' skyphos'' (), denoting a kind of drinking cup and alluding to the cup shape of the organism. Scyphozoans have existed from the earliest Cambrian to the present. Biology Most species of Scyphozoa have two life-history phases, including the planktonic medusa or polyp form, which is most evident in the warm summer months, and an inconspicuous, but longer-lived, bottom-dwelling polyp, which seasonally gives rise to new medusae. Most of the large, often colorful, and conspicuous jellyfish found in coastal waters throughout the world are Scyphozoa. They typically range from in diameter, but the largest species, ''Cyanea capillata'' can reach across. Scyphomedusae are found throughout the world's oceans, from the surface to great depths; no Scyphozoa occur in freshwater (or on land). As medusae, they eat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symmetry (biology)
Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symmetry down its centre, or a pine cone displays a clear symmetrical spiral pattern. Internal features can also show symmetry, for example the tubes in the human body (responsible for transporting gases, nutrients, and waste products) which are cylindrical and have several planes of symmetry. Biological symmetry can be thought of as a balanced distribution of duplicate body parts or shapes within the body of an organism. Importantly, unlike in mathematics, symmetry in biology is always approximate. For example, plant leaves – while considered symmetrical – rarely match up exactly when folded in half. Symmetry is one class of patterns in nature whereby there is near-repetition of the pattern element, either by reflection or rotation. Wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
