- 行业: Printing & publishing
- Number of terms: 178089
- Number of blossaries: 0
- Company Profile:
McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A class of the phylum Cnidaria traditionally containing four major groups—Coronatae, Rhizostomeae, Semaeostomeae, and Stauromedusae—all marine or estuarine. Most occur in two forms, the polyp, or scyphistoma, and the medusa, or scyphomedusa. However, some (the Stauromedusae) are polyplike and sessile throughout their lives, while others (such as the semaeostomes <i>Pelagia</i> and <i>Stellamedusa</i> and the coronate <i>Periphylla periphylla</i>) are always pelagic and lack the sessile scyphistoma stage. Among the Cnidaria, the Scyphozoa are characterized by having well-developed medusae of large size and fairly well organized scyphistomae of small size. The Scyphozoa are most closely related to the other medusae-containing classes—Cubozoa and Hydrozoa—within the Cnidaria, all of which evolved from a polyp-only ancestor currently represented by members of Class Anthozoa. Recent analyses of DNA and morphology indicate that the Stauromedusae group may represent an intermediate evolutionary stage between Class Anthozoa and Medusozoa (which would encompass Cubozoa, Hydrozoa, Coronatae, Rhizostomeae, and Semaeostomeae) and may, in fact, represent a distinct class of cnidarian (Class Staurozoa).
Industry:Science
A class of the phylum cnidaria which includes the fresh-water hydras, the marine hydroids, many of the smaller jellyfish, a few special corals, and the Portuguese man-of-war. The Hydrozoa may be divided into seven orders: the Hydroida, Milleporina, Stylasterina, Trachylina, Chondrophora, Siphonophora, and Spongiomorhipa. See separate article on each order.
Industry:Science
A class of the phylum Platyhelminthes commonly known as the flatworms. These animals are chiefly free-living and have simple life histories. The bodies are elongate and flat to oval or circular in cross section. Their length ranges from less than 0.04 in. (1 mm) to several centimeters, but may exceed 20 in. (50 cm) in land planaria. Large forms are often brightly colored. Smaller forms may have black, gray, or brown parenchymal pigment or may be white or transparent except for the color of ingested food and symbiotic algae. This class, which numbers some 3400 described species, is ordinarily subdivided into the 12 orders: Acoela, Catenulida, Haplopharyngida, Lecithoepitheliata, Macrostomida, Nemertodermatida, Neorhabdocoela, Polycladida, Prolecithophora, Proseriata, Temnocephalida, and Tricladida.
Industry:Science
A class of the phylum Platyhelminthes commonly referred to as tapeworms. All members are endoparasites, usually in the digestive tract of vertebrates. The class has been subdivided as follows: <ul class="articlebody"><ul class="articlebody"><li>Class Cestoidea</li><ul class="articlebody"><li>Subclass Cestodaria</li><ul class="articlebody"><li>Order: Amphilinidea</li><ul class="articlebody"><li>Gyrocotylidea</li></ul></ul></ul><ul class="articlebody"><li>Subclass Cestoda</li><ul class="articlebody"><li>Order: Proteocephaloidea</li><ul class="articlebody"><li>Tetraphyllidea</li><li>Lecanicephaloidea</li><li>Trypanorhyncha</li><li>Diphyllidea</li><li>Pseudophyllidea</li><li>Cyclophyllidea</li><li>Nippotaeniidea</li></ul></ul></ul></ul></ul> See separate articles on each group listed.
Industry:Science
A class of the phylum Porifera, including exclusively marine sponges with a skeleton composed of spicules of calcium carbonate to which can be added a solid basal calcitic skeleton. Calcarea vary from radially symmetrical vase-shaped species, to aggregates made up of a reticulum of thin tubes, to irregular massive forms. Calcareous sponges are mostly small and inhabit the shallow waters of all seas, from tidal areas to depths of 660 ft (200 m), with a few species extending down to at least 13,200 ft (4000 m).
Industry:Science
A class of the phylum Porifera, including sponges with a skeleton of one- to four-rayed siliceous spicules or of spongin fibers or both. Several genera lack a skeleton, and it is through a study of these seemingly primitive forms that the complicated structure of most adult Demospongiae may be understood. The Demospongiae constitute the most abundant and widely distributed group of sponges, occurring in the sea from the tidal zone down to abyssal depths (at least to 18,000 ft or 5500 m). Three families have invaded fresh water. The species vary in size from thin encrustations several centimeters in diameter to huge cake-shaped forms which may measure up to as much as 6.6 ft (2 m) in diameter.
Industry:Science
A class of the phylum Radiozoa in the Actinopoda. The kingdom Protozoa contains 18 phyla. One of the parvkingdoms (a hierarchical classification between kingdom and superphylum that is controversial and not officially recognized as such) is the Actinopoda (originally a class) containing two phyla: Heliozoa and Radiozoa. Within the Radiozoa is the class Acantharea. These marine protozoans possess a nonliving, organic capsular wall surrounding a central mass of cytoplasm. The intracapsular cytoplasm is connected to the extracellular cytoplasm by fine cytoplasmic strands passing through pores in the capsular wall. When viewed with the electron microscope, the capsular wall in some species appears to be made of many layers, each composed of a fine fibrillar network. The skeletons are made of celestite (strontium sulfate) instead of silica. The basic structural elements are 20 rods that pass through the capsule to the center in regular arrangements (polar and equatorial; see <b>illustration</b>). An equatorial rod forms a 90° angle with a polar rod, and other groups are arranged with similar exactness. This type of cytoskeleton may be modified by the addition of a latticework, composed of plates, each fused with a skeletal rod. Some genera show a double latticework, concentric with the central capsule. The skeletons do not contribute substantially to the paleontological record in marine sediments since celestite is dissolved by seawater. Dissolution is pronounced below 617 ft (188 m) depth. While the protozoan is still alive, however, the cytoplasm appears to protect the skeleton from dissolution.
Industry:Science
A class of the phylum Rhynchocoela which is divided into the orders Hoplonemertini (free-living) and Bdellonemertini or Bdellomorpha (symbiotic). The proboscis in the Hoplonemertini is armed with stylets, and in both orders the mouth is anterior to the brain, the nervous system is inside the body wall musculature, and the vascular system is well developed.
Industry:Science
A class of the phylum Rhynchocoela which is divided into the orders Palaeonemertini and Heteronemertini. The simple tubular proboscis lacks stylets and resembles the body wall in structure. The mouth is posterior to the brain. The nervous system lies either immediately below the epidermis or among the musculature of the body wall. The vascular system is well developed.
Industry:Science
A class of the phylum Rotifera characterized by a single gonad and mixed sexual and asexual reproduction. Monogonont rotifers are a major invertebrate component of freshwater and coastal marine ecosystems as judged by biomass, ecological importance, and number of species. Some species of <i>Brachionus</i> are grown commercially at rates of more than 100,000 per day as food for aquaculture of larval marine finfish and crustaceans.
Industry:Science
